Eberspacher Fault codes

Fault codes are generated by modern Eberspacher heaters (eg D*LC, D*LCC, Airtronics and Hydronics), these have a blue/white wire for connection to diagnostic testing equipment such as the 801 and some other controllers. Models prior to these have no diagnostics.

DO NOT wipe the fault codes without permanently recording them, this information can contain valuable clues for anyone diagnosing problems.

Some serious faults lock out the heater for safety reasons, always clear those faults before resetting.

Description 'open circuit' means no electrical path exists, like a wire disconnected or broken.

Description 'short circuit' means an electrical path exists, like two uninsulated wires touching together.

Connector S1 is on the cable from the Airtronic. Connector B1 joins this to the wiring loom.

Early model Airtronic ECUs have a plastic cable covering, later generation ECUs have a tape covering and are said to be more reliable.

Use the fault codes as a starting point, look at our other pages for more help if required.

Be aware that where the code shows a component has failed the ECU is unable to identify if it is the component itself that has failed or the electronic circuitry inside the ECU between the main microprocessor brain and the wiring is damaged. Also much of the ECU must be working to be able to send fault codes.

Airtronic D2 D4 and earlier heaters do not have fault codes greater than 99, if displayed and you do not have an Airtronic D2L or D4L look at the Weird faults section on the Faults page.

This fault code list is for Airtronic and Hydronic models but most fault codes apply to other models.

(Update 2022 The new D2L and D4L fault codes are completely different so these do not apply)

I found the Fault code page in the Eberspacher D2 manual has many errors, mostly probably due to translation into English, that mean some of the explanations in the manual are almost meaningless to general users. I used the information from that manual but I corrected obvious errors plus added material from our own experience.

Tip If you want a paper copy of this long webpage on multiple sheets using the Chrome browser, select the circle with 3 dots on the upper rhs, select print.

If you have any faulty parts except for glowpin screens or gaskets please donate them to us for science, we learn a lot from faulty parts.

		Eberspacher Airtronic Heater Fault Codes
	Fault table corrected plus additional information by letonkinoisvarnish.uk	DO NOT wipe the fault codes without permanently recording them, this information can be valuable for anyone diagnosing problems. Some serious faults lock out the heater for safety reasons, clear before resetting. Table is for D2 D4 heaters but most non specific details will apply to other air heaters

Code	Fault description	Comments and remedial action
00	No faults
04	Short circuit Fresh air outlet	Check wiring on Airtronic Connector B1 pin 16 for short circuit to earth. If ok replace ECU
05	Short circuit Car alarm output	Check wiring on Airtronic Connector B1 pin 15 for short circuit to earth. If ok replace ECU
06	Altitude sensor data H-kit heater only	Control box has not received any explicable altitude information. • Read out fault memory in the air pressure sensor using the EDiTH diagnostics tool and correct fault.
09	Cut off ADR This can also be a spurious fault code	a)ADR shutdown Airtronic connector B1 pin 13 or 14 , wires are usually not connected to wiring loom as ADR is only used for vehicles carrying hazardous materials. b)Fault code 09 can also be generated spuriously, usually after a heater is disconnected from power with the heater switch in the on position. A typical cause is disconnecting a plug after the heater has failed to start without turning off the switch on the controller. It can sometimes be erased by a diagnostic unit. Sometimes the code will not clear and a number of faults need to be introduced to move the fault to the end of the fault code memory and be over written as the heater can only hold 5 faults. If unsuccessful replace the ECU.
10	Overvoltage cut off	Voltage over 16 volts for at least 20 seconds, (32 volt for 24 volt heaters) Check alternator regulator or disconnect battery charger. Possibly 12 volt heater on 24 volt battery but this usually destroys the ECU.
11	Undervoltage cut off (Low voltage at heater)	Voltage under 10.5 volts continuously for at least 20 seconds (21 volts for 24 volt heaters) Extremely common fault, usually due to a discharged battery but many other reasons described on our low voltage faults page. IMPORTANT measure at the heater, not at the battery terminals where the voltage can be a lot higher. Usually occurs during starting when glowpin is on. The measurement method described in the Eberspacher Airtronic fault code list is almost useless, the heater must be connected and switched on so drawing current.
12	Overheating at overheat sensor (Software threshold value)	Temperature of the overheating sensor too high. Check heating air path for crushed pipes or blockages, air outlets closed or blocked. Often caused by putting objects against heating outlets. Every heater has specified limits on duct lengths, diameter, bends etc and exceeding these limits restricts air flow and can damage the ECU. Just replacing a straight outlet hood with right angle version can often put the piping outside spec. More info on our ducting pages including calculations and measuring heated air temperature for checking ducting. Check pumped fuel volume. Check Overheat sensor resistance. Check blower fan as fault code 33. The heater can be reset from fault codes 12 and 13 by switching off and on. Overheating is a serious safety issue and can damage the ECU so find and eliminate the cause before resetting. More info on our faults page, mainly in the "Faults when running" section.
13	Overheating at flame sensor (Software threshold value)	Temperature of the flame sensor too high. Check as fault code 12. Check Flame sensor instead of overheat sensor.
14	Temperature difference between flame and overheat sensors too large	Temperature difference between flame and overheat sensors too large. Check as fault code 12. Check both Flame sensor and Overheat sensor.
15	Overheat with excessive temperatures.	This code displayed when the heater is switched on after fault code 17 was displayed and there have been multiple overheats. On Hydronic water heaters the code is for 10 overheats in succession. Heater is locked. More info in fault codes 12 & 17.
17	Overheating lock out. (Hardware limit value)	The temperature exceeded the maximum the overheat sensor can measure. The ECU is locked for safety reasons. The ECU failed to recognise overheating fault code 012 or 013. My explanation on why 017 occurs is on the faults page. Heat may have damaged the ECU, if not it can be unlocked using appropriate equipment. IMPORTANT Identify and clear the cause of overheating before trying to reset. This lockout is for a very serious safety problem. More info on our Faults page.
19*	Glowpin energy too low	*New generation ECUs only. Current drawn by the glowpin is too low to ignite the fuel during startup. Check connections and glowpin resistance. Take care not to damage the wires. If all ok replace ECU
20	Glowpin interruption (Glowpin open circuit)	Check glowpin connector is fully pushed into Airtronic ECU, plug has thick brown and white wires. Photos on Airtronic servicing pages. Check for broken wires. Take care not to damage the wires. Check glowpin resistance, 12 volt 0.42 to 0.7 ohms, 24 volt 1.2 to 2.5 ohm. (Measurement errors may show a higher resistance, details on faults page.) If all ok replace ECU
21	Glowpin short circuit to earth	Check glowpin for physical damage Check wiring for damage, on an Airtronic usually close to glowpin due to removal without a modified socket. Check for water and corrosion in connectors and heater. Check glowpin resistance as in code 20 If all ok replace ECU
22*	Glowpin short circuit to battery positive supply	*New generation ECUs only. Check wiring for insulation damage. Take care not to damage the wires. Check for water in connectors and heater. If ok replace ECU.
25*	Diagnostic cable short circuit to battery positive supply	*New generation ECUs only. Check blue/white wire is not damaged or loose and touching the +12 volt supply. Check for water in connectors and heater. This fault might only be read after the fault has cleared as it would disable the diagnostics signal.
31	Blower motor interruption. (Blower open circuit)	Check blower (fan) motor plug is fully pushed into Airtronic ECU, plug has black and white wires. Photos on Airtronic servicing pages. Check wiring for damage. Check resistance of the motor is roughly 0.5 ohms. Worn motor brushes can give intermittent connections that do not show up on this test. Faulty motor segments may only show up while slowly rotating the shaft by hand. If ok connect a short circuit across the ECU fan connector pins and restart. If fault code changes to 32 fault is not ECU, probably intermittent motor. If code does not change Replace ECU. Brushes are the most likely reason for this problem but mechanical jamming of the motor as in fault 32 could cause the motor to burn out.
32	Blower (fan) motor short circuit to earth or drawing excessive current	Check wiring to fan motor for insulation damage. Check for water in connectors and heater. Check motor is free to rotate and not catching on case or ECU. Check bearings are not starting to seize. Check resistance of the blower motor is approximately 4 ohms.
33	Blower (fan) not rotating or rotating at wrong speed	Speed deviation greater than 10% from specified for more than 30 seconds. Check blower is free to rotate and not catching on case or ECU. Check for evidence of fan rubbing on the case. Check ECU is firmly secured with the retaining screw and wires to the sensors have not pushed the ECU towards the fan. The detector for the magnet is inside the ECU so check ECU is fitted correctly. Check blower motor plug is fully inserted into Airtronic ECU. Measure the Blower speed using a non contact rpm meter (tachometer), one cost £7 including post from China November 2017. D2 Power 4800 ±140, High 4000 ±120, Med 2800 ±80, Low 2000 ±60 rpm D4 Power 4400 ±130, High 3500 ±100, Med 2600 ±80, Low 1600 ±50 rpm D5 Speeds are not quoted in manual D1LCC Power 5000, High 4400, Medium 3000, Low 3000 rpm D3LCC Power 4200, High 4200, Medium 2200?, Low 3000 rpm If RPM is too high, check if magnet in impeller is mounted properly, photo Airtronic service pages. If RPM is too low, check air path for restrictions or blockage. Check wiring for breaks, loose connections, faulty insulation. Check as code 032. Erratic blower speed can also be caused by ECU earthing, see faults page Weird faults section. Blower brushes or bearings worn, replace or repair blower. If ok replace ECU.
34*	Blower (fan) motor short circuit to +12 volts	*New generation ECUs only. Check for water in heater. Manual says check wires for damage but unlikely to be cause in Airtronics as there is no +12v source close. If ok replace ECU. www.letonkinoisvarnish.uk
47	Fuel metering pump short circuit to earth or overload current	Disconnect the wires on the pump connector, if fault code 48 is displayed pump is faulty. (If the pump has to be replaced please donate the faulty one to us for science.) If code 47 remains displayed also disconnect the main loom connector B1 and then check the wiring to the pump with a test meter for a short circuit. Most likely cause is mechanical damage to the insulation where cables are clipped in position or uninsulated connectors on older Eberspacher pump types touching the chassis. Check for water in connectors and heater. If ok replace ECU.
48	Fuel metering pump interruption (Fuel pump open circuit)	Pump connector not fully pushed home or making a bad connection. Often occurs after disconnecting pump. Airtronic pumps use a locking spring, press it in whilst inserting connector, pictures on faults page. Disconnect the wires on the pump connector and measure the resistance of the pump. The resistance of an Eberspacher D1LCC, D2, D4 or D5 pump should measure 10 ± 0.5 ohms (24v 36 ± 1.8 ohms). If not ok check connections for corrosion, replace pump, see code 047. If ok reconnect the pump and disconnect the main Eberspacher loom connector B1. Measure resistance across the connector pins 5 and 10 going to the pump. If not ok wiring to pump is faulty, if ok check connectors S1 B1 for corrosion, replace ECU. If no test meter is available the pump can be connected to a 12 volt battery, it should make a loud click each time it is connected. (Make sure the pump is disconnected from the loom before doing this test or you can destroy the ECU. Also take care not to accidentally short circuit the battery). More info fuel page. If ok replace ECU.
49*	Fuel metering pump short circuit to positive battery	*New generation ECUs only. Check for pump wires loose or with damaged insulation. Check for water in connectors and heater. Check for incorrect wiring connections on new installations. If ok replace ECU
50	Too many start attempts. ECU locked out.	The ECU locks out after 255 consecutive start attempts (Airtronic heaters). The count is reset if any other fault occurs during this time. It can be unlocked with appropriate equipment.
51	Flame detected during switch on (time exceeded blowing cold)	Flame sensor resistance above 1274 ohms at switch on indicates the temperature is above 70 degrees C and the fan runs to cool it down. If temperature does not fall below 70 degrees within aprox 15 minutes heater is switched off. Check flame sensor, if ok replace ECU.
52	Safety time exceeded. Unit failed to start on both start attempt sequences.	No flame was detected during the two start attempt sequences, unit shut down after a cooling down cycle. This is simply a standard failure to start fault indication. The causes are detailed in Faults page.
53	Flame cutout in Power	The flame extinguished during the Power stage. The causes are detailed in Faults page in the section "Eberspacher starts normally but stops whilst running, it may try to restart."
54	Flame cutout in High	The flame extinguished during the High stage. Causes as fault 53.
55	Flame cutout in Medium	The flame extinguished during the Medium stage. Causes as fault 53.
56	Flame cutout in Low	The flame extinguished during the Low stage. Causes as fault 53.
57	Flame cutout in Start	Heat detected before fuel pump started. Heat is being transferred from the glowpin to the sensors, usually caused by chamber flooded with fuel. If a new installation fuel taken from a fuel pipe where fuel is under pressure, there may be fuel dripping from the exhaust when the vehicle engine is running. Do a fuel volume test, details fuel page (Expect massive amounts of smoke when heater starts)
60	External temperature sensor interruption (open circuit)	External temperature sensor disconnected while heater was running. If still open circuit it will be ignored during starting and heater will use its internal sensor. Disconnect Airtronic connector B1 and measure sensor resistance between B1 pins 6 and 12, it should be between 1600 and 2100 ohms (0 to +30 degrees C). If greater check sensor and grey and brown/white wires for breaks or corrosion. If ok ECU is faulty but it possibly can still be used with the internal sensor.
61	External temperature sensor short circuit	Disconnect connector B1 and measure resistance between B1 pins 6 and 12 If less than 486 ohms check wiring to sensor for damage. Check sensor, it should be between 1600 and 2100 ohms (0 to +30 deg C)
62	Temperature control interruption (open circuit)	Heater received the switch on signal from the controller but could not read the controller temperature setting. Check grey/red wire for a break or loose connection. For a rheostat type controller only, disconnect S1 B1 and measure resistance between B1 pin 6 and pin 7, the control should adjust from 1750 to 2180 ± 80 ohms. If ok replace ECU, otherwise with B1 still disconnected measure across rheostat pins with grey/red and brown/white wires. If not ok replace controller. For more modern types of controller follow instructions on faults page in section "Stage 2 Pre start failure". A D2 with this fault did not fail the pre start checks, unknown if other models do the same.
63	Temperature control short circuit Fault recognised only if it occurs in heating mode.	Detailed instructions on faults page in section "Stage 2 Pre start failure". Fault code indicates resistance value was less than 486 ohms. If heater is switched on with this fault ventilation mode is selected, (no fault code).
64	Flame sensor interruption(open circuit)	Detailed instructions on faults page in section "Stage 2 Pre start failure". Fault code indicates resistance value was greater than 7175 ohms.
65	Flame sensor short circuit	Detailed instructions on faults page in section "Stage 2 Pre start failure". Fault code indicates resistance value was less than 486 ohms.
71	Overheat sensor interruption(open circuit)	Detailed instructions on faults page in section "Stage 2 Pre start failure". Fault code indicates resistance value was greater than 223k ohms.
72	Overheat sensor short circuit	Detailed instructions on faults page in section "Stage 2 Pre start failure". Fault code indicates resistance value was less than 183 ohms. Remove blue connector from ECU, if code 071 is displayed replace combi sensor. If code 072 continues to be displayed replace ECU.
74	ECU defective	Overheating threshold not detected by ECU, replace ECU
90	ECU problem	Sometimes this fault can be reset with unlocking equipment like 801 controller. If not replace ECU
91	External interference voltage	ECU affected by interfering voltages from vehicles electrical system. Possible causes are poor battery or battery charger. See also fault 99. Severe instances might result in ECU damage.
92	ECU defective (Rom error)	Memory inside ECU failed. Replace ECU
93*	ECU defective	*New generation ECUs only. Replace ECU
94	ECU defective EEPROM error	Programmable memory failed. Replace ECU
95	ECU defective	*New generation ECUs only. Replace ECU
96	Internal temperature sensor faulty	Internal temperature sensor faulty. In theory you can use an external sensor. In practice both sensor circuits are usually faulty, replace ECU
97	ECU defective	Replace ECU
98*	ECU defective	*New generation ECUs only. Replace ECU
99*	Too many resets in sequence	*New generation ECUs only. Voltage short term drops below 5 - 6 volts (for 12 volt heaters) or 7 - 8 volts (for 24 volt). Check +12 volt and earth (0 volts) from the battery for loose or corroded connections. Check fuse and fuseholder, battery terminals, battery cables for damage. Check battery condition. Leisure batteries, especially ones continuously float charged, can deteriorate with no other obvious signs unlike engine batteries which fail to start the engine so are quickly replaced. Simple voltage checks may still show ok even if battery is bad. Locate and clear cause before trying to reset, severe instances have caused ECU damage.
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		Eberspacher Water Heater Fault Codes
	Fault table corrected plus additional information by letonkinoisvarnish.uk	DO NOT wipe the fault codes without permanently recording them, this information can be valuable for anyone diagnosing problems. Some serious faults lock out the heater for safety reasons, clear before resetting.

Code	Fault description	Comments and remedial action
00	No faults
04	Short circuit Fresh air outlet	Possibly code only air heaters
05	Short circuit Burglar alarm output	*Hydronic II only. Not normally used. Check wiring for short circuit to earth. If ok replace ECU
09	Cut off ADR This can also be a spurious fault code	a)*Hydronic II models. ADR shutdown, wires are usually not connected in wiring loom as ADR is only used for vehicles carrying hazardous materials. b)Fault code 09 can also be generated, usually after a heater is disconnected from power with the heater switch in the on position. A typical cause is disconnecting a plug after the heater has failed to start without turning off the switch on the controller. It can sometimes be erased by a diagnostic unit. Sometimes the code will not clear and a number of faults need to be introduced to move the fault to the end of the fault code memory and be over written as the heater can only hold 5 faults. If unsuccessful replace the ECU.
10	Overvoltage cut off	Voltage over 16 volts for at least 20 seconds, (32 volt for 24 volt heaters) *Hydronic II models 15 or 30 volts for 10 seconds. Check alternator regulator or disconnect battery charger. Possibly 12 volt heater on a 24 volt battery.
11	Undervoltage cut off (Low voltage at heater)	Voltage under 10.5 volts continuously for at least 20 seconds, 21 volts for 24 volt heaters, Hydronic II models 10 , 20 volts. Extremely common fault, usually due to a discharged battery but many other reasons described on our low voltage faults page. IMPORTANT measure at the heater, not at the battery terminals where the voltage can be a lot higher. Usually occurs during starting when glowpin is on. The measurement method described in the Eberspacher Airtronic fault code list is almost useless, the heater must be connected and switched on so drawing current.
12	Overheating at overheat sensor (Software threshold value)	Temperature of the overheating sensor greater than 125 deg C. Heater can be restarted by switching off and on again. This is a safety issue so do not keep restarting if it continues to occur. Check all hoses for water leaks. Check water circuit is properly vented, ie no air. Check header tank water level. Check valves, especially isolating valves, have not been shut off or turned down. Check for blockages in water circuit. Check water pump functions. Check if installing thermostat and non return valve that position and direction is correct. Measure resistance of overheat sensor. Resistance approx 0°C 33,000 ohm, 20°C 12,450 ohm, 50°C 3600 ohm, 100°C 670 ohm If value is a great deal larger replace that sensor. Overheating is a serious safety issue and can damage the ECU so find and eliminate the cause before resetting. More info on our faults page, mainly in the "Faults when running" section.
13	Overheating at flame sensor (Software threshold value)	Temperature of the flame sensor too high. Check Flame sensor, values same as overheat sensor, fault 12
14	Temperature difference between flame and overheat sensors too large	Temperature difference between flame and overheat sensors greater than 25°C. Prerequisite for this fault code is that the Hydronic is operating and the water temperature at the overheating sensor has reached minimum 80°C. Check as fault codes 12 & 13
15	Overheating lock out Too many faults	The ECU is locked for safety reasons. Heater has overheated more than 10 times in succession. IMPORTANT Identify and clear the cause of overheating before trying to reset. This lockout is for a serious safety problem. Investigate causes as fault code 12. Unlock using appropriate diagnostic equipment.
17	Overheating lock out. (Hardware limit value)	The temperature exceeded 130°C the maximum the overheat sensor can measure.The ECU is locked for safety reasons. The ECU failed to recognise overheating fault code 012 or 013. My explanation on why 017 occurs is on the faults page. Heat may have damaged the ECU, if not it can be unlocked using appropriate equipment. IMPORTANT Identify and clear the cause of overheating before trying to reset. This lockout is for a very serious safety problem. More info on our Faults page.
19	Glowpin 1 Ignition energy too low	*Hydronic II only. Energy input less than 2000 watts. The glowpin heats the burner during starting so the fuel can ignite. The flame sensor measured the temperature which is not high enough to ignite the fuel. Check glowpin. Check vent hole is clear, Check exhaust and combustion air path. Check pumped fuel supply volume. Check flame sensor. If all ok replace ECU
20	Glowpin interruption (Glowpin open circuit)	Check for broken wires. Check glowpin resistance, 12 volt 0.42 to 0.7 ohms, 24 volt 1.2 to 2.5 ohm. Measurement details and photos on faults page. If all ok replace ECU
21	Glowpin short circuit to earth	Check glowpin for physical damage Check glowpin resistance as in code 20 Check wiring for damage, usually close to glowpin due to removal without a modified socket. Check for water in connectors and heater. If all ok replace ECU
22	Glowpin short circuit to battery positive supply	*Hydronic II only. Check wiring for insulation damage. Check for water in connectors and heater. If ok replace ECU.
23	Glowpin 2 interruption (Glowpin open circuit)	*Hydronic II with second glowpin only. Check as code 20
25*	Diagnostic cable short circuit to battery positive supply	*Hydronic II only. Check blue/white wire is not damaged and touching the +12 volt supply. Check for water in connectors and heater. This fault might only be read after the fault has cleared as it would disable the diagnostics signal.
26*	Glowpin 2 short circuit to battery positive supply	*Hydronic II with second glowpin only. Check as code 022
29	Glowpin 2 ignition energy too low	*Hydronic II with second glowpin only. Check as code 19
30	Blower fan motor not rotating or rotating at wrong speed	* This code not used Hydronic II Check fan is free to rotate and not catching on anything. Check wiring for breaks, loose connections, faulty insulation. Check combustion air path, both inlet and exhaust, are not obstructed. Blower brushes or bearings worn, repairs blowers pages. If testing motor on a dc supply use 6 or 8v, not 12v. (Measurement as described in D4WSC D5WSC manual is completely wrong)
31	Blower motor interruption. (Blower open circuit)	Check blower (fan) motor plug is fully pushed into ECU, plug has black and white wires. Photos on Airtronic servicing pages. Check wiring for damage. Check resistance of the motor is approximately 4 ohms. Worn motor brushes can give intermittent connections that do not show up on this test. Faulty motor segments may only show up while slowly rotating the shaft by hand. If ok connect a short circuit across the ECU fan connector pins and restart. If fault code changes to 32 fault is not ECU, probably intermittent motor. If code does not change Replace ECU.
32	Blower (fan) motor short circuit to earth or drawing excessive current	Check wiring to blower for insulation damage. Check for water leaking inside heater and on connectors. Check motor is free to rotate and not catching on anything. Check bearings are not starting to seize. Check wiring to blower for insulation damage. Check resistance of blower motor which should be roughly 0.5 ohms Use accurate measurement technique shown on faults page. If testing blower use high current 6 or 8v dc supply, not 12v. Do not try to dismantle blower without reading our blower pages. Replace motor.
33	Blower (fan) not rotating or rotating at wrong speed	*Hydronic II only. Check fan is free to rotate and not catching on anything. Check wiring for breaks, loose connections, faulty insulation. Check combustion air path, both inlet and exhaust, are not obstructed. Blower bearings worn.
34*	Blower (fan) motor short circuit to +12 volts	*Hydronic II only. Check for water in heater Check wires for damage and in contact with +12v. If ok replace ECU. www.letonkinoisvarnish.uk
37	Water pump not working	*Hydronic II only. Check water pump. Apply 12v to water pump, connector B1 pins 12 & 13 (Power input max 4 amps)
38	Relay for operating vehicle fan interruption (Open circuit)	* This code not used Hydronic II & some Hydronics Check wiring to relay for breaks or loose connection. Check relay. Disconnect 8 pin connector, measure on the connector part not going to the ECU. Measure resistance between pins 2 and 3. Depending upon type of relay a good reading should typically be around 80 ohms. If greater than 1000 ohms check relay coil resistance or replace relay.
39	Relay for operating vehicle fan short circuit, overload or short circuit to ground.	* this code not used Hydronic II Check wiring to relay for insulation damage or broken connection touching. Check for water leaking inside heater and on connectors. Check relay Remove relay, if fault 038 displayed replace relay. Alternative method Disconnect 8 pin connector, measure on the connector part not going to the ECU. Measure resistance between pins 2 and 3. Depending upon type of relay a good reading should typically be around 80 ohms. If lower than 20 ohms remove relay. Then if resistance becomes very high replace relay.
41	Water pump interruption (Open circuit)	Check wiring to water pump for damage or breaks. Check resistance of the water pump, rotate shaft by hand while checking. Disconnect 14 pin connector, measure on the connector part not going to the ECU. Measure resistance between pins 10 and 11. No resistance figure is quoted but probably about 0.5 ohms. If testing pump on 12v battery without water keep test very short.
42	Water pump short circuit to earth or drawing excessive current.	Check wiring to water pump for damage to insulation. Check for water leaking inside heater and on connectors. Check if pump is running dry. Vent heater, check header tank water level. Disconnect connection in water pump cable harness. If error code 41 is then shown replace water pump.
43	Water pump short circuit	Check wiring to water pump for damage to insulation. Check for water leaking inside heater and on connectors.
47	Fuel metering pump short circuit to earth or overload current	Disconnect the wires on the pump connector, if fault code 48 is displayed pump is faulty. (If the pump has to be replaced please donate the faulty one to us for science.) If code 47 remains displayed also disconnect the main loom connector B1 and then check the wiring to the pump with a test meter for a short circuit. Most likely cause is mechanical damage to the insulation where cables are clipped in position or uninsulated connectors on older Eberspacher pump types touching the chassis. Check for water in connectors and heater. If ok replace ECU.
48	Fuel metering pump interruption (Fuel pump open circuit)	Pump connector not fully pushed home or making a bad connection. Often occurs after disconnecting pump. Airtronic pumps use a locking spring, press it in whilst inserting connector, pictures on faults page. Disconnect the wires on the pump connector and measure the resistance of the pump. The resistance of an Eberspacher D1LCC, D2, D4 or D5 pump should measure 10 ± 0.5 ohms (24v 36 ± 1.8 ohms). If not ok check connections for corrosion, replace pump, see code 047. If ok reconnect the pump and disconnect the main Eberspacher loom connector B1. Measure resistance across the connector pins 5 and 10 going to the pump. If not ok wiring to pump is faulty, if ok check connectors S1 B1 for corrosion, replace ECU. If no test meter is available the pump can be connected to a 12 volt battery, it should make a loud click each time it is connected. (Make sure the pump is disconnected before doing this test or you can destroy the ECU. Also take care not to accidentally short circuit the battery). More info Fuel 2 page. If ok replace ECU.
49	Fuel metering pump short circuit to positive battery	Check for pump wires loose or with damaged insulation. Check for water in connectors and heater. Check for incorrect wiring connections on new installations. If ok replace ECU
50	Too many start attempts. ECU locked out.	*Hydronic II - The ECU locks out after an unspecified number of repeated start attempts without flame detection. Hydronic - The ECU locks out after 10 consecutive start attempt failures. Manual is not clear, I think a failed start with the second start attempt counts as one failure. IMPORTANT Identify and clear the cause before trying to reset. This lockout is for your safety as each attempt leaves unburnt fuel. The count is reset if any other fault occurs during this time. It can be unlocked with appropriate equipment.
51	Flame detected during switch on (time exceeded blowing cold)	Flame sensor resistance above 1274 ohms at switch on indicates the temperature is above 70 degrees C and the fan runs to cool it down. If temperature does not fall below 70 degrees within 15 minutes heater is switched off. Check flame sensor, if ok replace ECU.
52	Safety time exceeded. Unit failed to start on both start attempt sequences.	No flame was detected during the two start attempt sequences, flame sensor value was below 80°C. Unit shut down after a cooling down cycle. This is simply a standard failure to start fault indication. The causes are detailed in faults page.
53	Flame cutout in highest power stage	The flame extinguished during the boost / highest power stage. Fault code is deleted if automatic restart is ok. The causes are detailed in faults page in the section "Eberspacher starts normally but stops whilst running, it may try to restart."
54 55 56 57 58	Flame cutout in high medium or medium 1 medium 2 medium 3 low power	The flame extinguished while operating. Number of Power stages and stage naming is different for some heaters. Fault deletion and causes same as fault 053.
59	*Hydronic II only Too rapid rise in water temperature	Vent air from system. Open heater slide valve Check water flow rate. Check water temperature sensor, resistance as code 12
60	Temperature sensor interruption (open circuit)	Check sensor wiring for damage or breaks. Check temperature sensor, values same as overheat sensor, fault 12. Alternatively place short circuit across sensor (or connector pins for some models). If heater then shows error code 61 check and replace sensor. If 60 still appears replace ECU.
61	Temperature sensor short circuit, overload or short circuit to ground.	Check wiring to temperature sensor for damage to insulation. Check for water leaking inside heater and on connectors. Check temperature sensor resistance as code 12. If resistance is much lower replace sensor. Possibly may need ecu unlocking after this fault.
64	Flame sensor interruption(open circuit)	Check sensor wiring for damage or breaks. Check Flame sensor resistance as code 12. If resistance is much higher replace sensor.
65	Flame sensor short circuit	Check wiring to flame sensor for damage to insulation. Check for water leaking inside heater and on connectors. Check flame sensor resistance as code 12. If resistance is much lower replace sensor.
71	Overheat sensor interruption(open circuit)	Overheating sensor signals temperature value outside the measuring range. Check Overheat sensor resistance as fault code 12 Check sensor wiring for breaks and damage
72	Overheat sensor short circuit	Overheating sensor signals temperature value outside the measuring range. Check Overheat sensor resistance as fault code 12 Check sensor wiring for breaks and damage
74	ECU defective	Overheating threshold not detected by ECU, replace ECU
90	ECU problem	Sometimes this fault can be reset with unlocking equipment like 801 controller. If not replace ECU
91	External interference voltage	ECU affected by interfering voltages from vehicles electrical system. Possible causes poor battery or battery charger. See also fault 99. Severe instances might result in ECU damage.
92	ECU defective (Rom error)	Memory inside ECU failed Replace ECU
93*	ECU defective	At least one RAM cell is not working, Replace ECU
94	ECU defective EEPROM error	Programmable memory failed, checksum error, Replace ECU
95	Invalid data record	Checksum error, Replace ECU
96	Internal temperature sensor faulty / ECU too hot	Internal temperature sensor faulty / ECU too hot Replace ECU
97	Internal device errror	Replace ECU
98*	Main relay is faulty	Replace ECU
99*	Too many resets in sequence Heater Locked	Voltage short term drops below 5 - 6 volts (for 12 volt heaters) or 7 - 8 volts (for 24 volt). Check +12 volt and earth (0 volts) cables from the battery for loose or corroded connections. Check fuse and fuseholder, battery terminals, battery cables for damage. Check battery condition. Leisure batteries can deteriorate with no other obvious signs. Simple voltage checks may still show ok even if battery is bad. Locate and clear cause before trying to reset, severe instances have caused ECU damage.
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Water heater codes and diagnostic data may not be as accurate as the Air heater table as we do not use water heaters. Please feedback any suggestions or corrections to improve the table