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Eberspacher wiring modern air heaters

Airtronic D2  D4  D5, D1LCC D3LCC, D1LC D3LC D5LC, (not D2L D4L)

Wiring connections cause many people problems when changing or maintaining their systems.

The installation manuals cover many of the details and I recommend downloading and studying the manual before starting, see Manuals page.

These details do not apply to the latest heaters, D2L and D4L as they use a completely different control method and wiring system.

Warning:- If you have an Eberspacher and it has a truck manufacturers name on the label it may be non standard so these wiring details do not apply, see our Buying advice page for more details.

If you are not confident of your ability to install things safely or cannot understand my simplified guides leave it to the professionals! A mistake will usually not be like the photo but mistakes can damage the ECU and be extremely expensive. Connecting the battery the wrong way round while testing is a common way of destroying the ECU. Check and then double check before connecting or inserting the fuse.

Always remove the fuse or disconnect the battery before doing work on the wiring.

Wiring Looms

Heaters looms may be professional or user made so there are a variety of types and lengths even for the same heater but the wiring colours are usually reasonably standard.

Change all 12 volt references to 24 volt for 24 volt versions.

Battery supply.

The looms have 2 main battery wires,  +12v  and earth. These should be easy to identify, they will be the thickest wires in the loom, red +12 volts, brown earth (or negative). Often they are too short and have to be lengthened. Include a blade type fuse in the +12 volt feed, 20 amp for D2 D4, 30 amp for all other air heater models including D5. Always use a high quality fuseholder. Cheaper low quality fuseholders are not suitable for high current equipment and may burn out or cause unreliable connections.

Do not skimp on power cable size as doing so can cause unreliable operation due to low voltage problems. Thinner cable is cheaper but you will regret using it later! (Full details on Low voltage page).

For a D2 / D4 Eberspacher recommend 4 mm2 wires for up to 2.5m individual wire length; ie 2.5 m positive wire and 2.5 m return wire. Increase the cable size to 6 mm2 up to 4 m, and 10 mm2 or more for longer runs. That should give a cable loss of 0.25v or less.

The length calculation should include cables from the battery terminal to the connection point.

All other air models take about 20 amps during starting so recommended cable sizes are doubled.

The heater needs power for about 4 minutes for the cool down cycle after switching off so main +12v cable is not supplied via ignition switch.

The thin red wire that supplies power to the controller is usually joined to the main +12v input cable but on some looms it is brought out separately so it can be connected from the ignition switch if required.

The controller and other wiring carries less current and can be run in almost any normal cable thickness.

Eberspacher D1LCC & D3LCC

Rheostat controller fitted into connector.

Eberspacher Wiring Colour Codes

Eberspacher manuals use these codes to indicate wiring colours.

Eberspacher Airtronic cable connector S1

Airtronic D2  D4  D5

D2  D4  D5 Airtronic cable connector S1

Eberspacher D1LC   D3LC  D5LC

D1LC  D3LC and D5LC heaters wiring colours are the same as the D1LCC D3LCC.

These older models had external electronics, the ECU pin numbers quoted above do not apply.

The diagnostics blue/white wire on these models works with modern controllers or test equipment but will also provide an output suitable for flashing codes via a light.

Connector terminal removers

It is virtually impossible to remove terminals from connectors without the correct extractor tool.

If you need to remove a terminal and know a friendly mechanic he might be able to do it for you.

Modern water heaters have several cables in one connector so parts like the motor cannot be removed.

I tried 2 types of reasonably priced extractors but they were not suitable.

At best I could remove about 1 terminal out of 10.

If anyone has working extractors and could donate them we would be very grateful.

Update 2018:   A user successfully modified his green extractor by cutting it with a hacksaw to increase the length  of the short prongs and was then able to extract the pins.

When I find where I have stored mine I will try modifying it.

This is described in the Mouser catalogue as a Junior Power Timer housing AMP 929504-6

 Others are called Junior timer connectors.

None of these extractors worked for me on Eberspacher connectors.

Users sometimes pick up odd lengths of cable with no indication of size. As an example here are three mains cables to show relative size.  Cable sizes are the wire cross sectional area, not the diameter.

The 2.5 mm2 cable is included for comparison as it is used for household ring main circuits so many people will know its size. 4 mm2 cable was not available for these photos. As a rough guide the 10 mm2 wire which has 7 strands measures 4 mm across the wire bundle and the 6 mm2 cable 3 mm across. If the cable has lots of thinner strands the wire bundle could be smaller.

Pump wiring

There are 2 wires for the pump,  usually green/red and green,  green/red and brown or green and green depending on model. The pump is not polarity dependent, connect wires to the terminals either way round.

The pump may be mounted under the chassis, ensure adequate mechanical protection to the cables and connections.

Controller connections

The remainder of the wires that need to be identified are for connections to the controller.

This is where most of the confusion arises as there are many different controllers and connector types.

I have tried several different ideas to simplify the wiring for users with limited technical knowledge with only partial success. This time I am going back to the method of identifying these wires Eberspacher used in their earlier manuals. For each heater model the wires needed are identified with a number, a1 to a9.

Each controller will also use the same identifier system. See Controller page. This will allow a heater model to be connected to any compatible controller by joining wires with the same number.

The controller wiring carries low currents so can be run in almost any cable thickness.

Each heater generally has 4 wires for the controller plus wires for an optional remote sensor and diagnostics

You can ignore wires that are not used, just make sure they are insulated.

Three additional wires may be used.

* The wire from the Airtronic to Pin 6 on S1 may be coloured brown but functions as the brown/white.

   Yellow wire current is low, Airtronic draws about 7 ma to switch heater on

Eberspacher Airtronic D2  D4  D5 loom

There are many versions of the loom, some looms will be user made. If the colours / connector are obviously wrong check if the heater is a non standard version, see Buying advice pages.

Connectors at the controller end of the loom may have been cut off and different connectors could be used so use the cable colours as the main identification. Check with the pin numbers at the Eberspacher heater end of the cable if unsure.

Some power wiring joints are hidden inside the loom sheath.

We have encountered three looms without a brown/white wire. Using the brown wire (pin 10) instead of the brown/white (pin 6) can cause problems. Details are in the Weird faults section in Faults page.

One of our D2 / D4 looms.

Left connector plugs into the Airtronic connector S1.

Upper right connector is for the controller.

White connector carries power and remote sensor.

Central connector is for fuel pump.

D1LCC loom connector inside heater casing plugs into the ECU.

White wires are for the glow pin.

Other end of our D1LCC loom, ex BT.

Large black connector temperature rheostat.

Smaller black connector diagnostic testing.

Twin wire connector battery supply.

Two single connectors fuel pump.

Triple wire connector was for BT 1 hour timer (now bypassed)

Eberspacher D1LCC loom.

They were usually fitted with a rheostat temperature controller.

They had an old round type fuseholder with 20 Amp ceramic fuses. These are often corroded and unreliable so replace with a good quality blade type fuseholder. It is generally recommend to increase the blade fuse rating to 30 Amps as they have different thermal characteristics to ceramic fuses.

Some power wiring joints are hidden inside the loom.

Many second hand D1LCC heaters are ex BT. These were fitted with a timer that allowed a maximum of 1 hours heating, the timer reset after a further hour. The timer could be removed and bypassed by joining the purple and yellow wires together as shown.

Ex BT looms do not have the grey external temperature sensor wire.

One loom we have also had no brown/white wire. The controller used the brown wire instead. I installed a new brown/white wire.

D1LCC heaters sold now will probably be at least third hand so the wiring looms need checking as they may have been butchered.

Rheostat connector. On non BT loom yellow wire goes direct to pin 6

(in place of the purple wire)

rt     red

bl     blue

ws   white

sw   black

gn   green

gr    grey

ge   yellow

vi     violet

br    brown

li     purple

Brown and Brown/white wire confusion

Users sometimes encounter installations where the brown wire has been used to the controller instead of the brown/white and are unsure what to do. The confusion is due to there being two earth wires.

Brown is a general earth point and is used for the earth connection to higher current items like fuel pumps.

The brown/white is also an earth point but is taken from a  technical earth inside the ECU which is not so affected by electrical interference.

If controllers and temperature sensors are connected to the brown wire they will probably work but occasionally there can be weird unpredictable problems as described in Faults page Weird faults section.

You should use the brown/white for controllers.

Some controllers use both wires, the brown wire is just used for the indicator light which is ok.

Second Eberspacher controller

When installing it might be worth considering if adding a second controller will be a useful addition.

Even if it is added at a later date installing the switch will be easier if it is done with the main wiring.

Details on Controllers 4 page.

At the same time check for any remote temperature sensor requirements, remote sensor page.

Standard Airtronic D2 D4 D5 connector S1

If the Airtronic heater does not have the standard connector it is OEM  like this DAF and the wiring details do not apply. See Buying pages for details.

Feedback on our Eberspacher advice pages has been very positive, keep it coming.

I would appreciate an email, contact details are on the Introduction page, if you found these articles useful. It helps me to gauge how much interest there is and keeps me motivated.

D2 / D4 loom connector B1

This plugs into the Airtronic connector S1