# Fixing Problems with Headlamp Range Control



## steveupton (Mar 23, 2010)

Having recently sorted out a problem with the headlamp range control not working on my car, thought I would put together a how to guide. Would be happy to hear from anyone who has any suggestions for improving it.

*HOW TO TRACE AND REPAIR FAULTS WITH HEADLAMP RANGE CONTROL*

As most of you are aware, if your car has xenon lights and self adjusting headlamps, as part of the changes to the MOT test, this function must now work, irrespective of whether the headlamps are adjusted correctly.

The adjustment system (or in Audi speak, Range Control) consists of 3 elements:-

1.	Suspension sensors G78 front and G76 rear that measure the up/down movement of the lower suspension arms.

2.	A Range Control unit J431 that interprets the electrical signals from the G78 and G76 sensors and commands the motors to adjust the headlamps up/down as appropriate.

3.	Motors in the Headlamp units that move the dipped beam projector lamps up/down.

Below is a diagram showing the various locations of the sensors and controller:-










In the above diagram, items 8, 23 and 35, the sensors, are all the same part number:- 4BO 907 503 A. Item 1 is the controller (J431), part number 4BO 907 357

If the headlamp auto levelling stops working, the problem usually lies with the G78 or G76 sensors or the associated bracketry that attaches them to the suspension, with even the latest MkI's 6 years old now, corrosion is beginning to affect the various brackets and clamps.

The first thing to do is a Vagcom (or VCDS) scan to see if the there is a problem showing up on the self test, the module to select is 55. Below is a typical fault showing that the front (G78) sensor is at fault:-

Address 55 -------------------------------------------------------
Controller: 4B0 907 357 
Component: LEUCHTWEITEREGLER D004
Coding: 00010
Shop #: WSC 01236
1 Fault Found:
00776 - Level Control System Sensor: Left Front (G78)
31-00 - Open or Short to Ground

If no fault is found, then suspect there is a problem with the brackets or clamps connecting either the front or rear sensors to the suspension arm. You can visually inspect either without removing a wheel but it is easier with the wheel removed, both sensors are located on the left hand side of the car looking from the rear to the front. Below are a couple of images showing their precise locations:-

G78 Front Sensor and associated hardware










G76 Rear Sensor and associated hardware on Quattro models










The J431 control unit is on the right hand side of the vehicle under the bench seat for the coupe and behind the right rear back panel for the roadster.

*REPLACING SENSORS*

Tools required: ¼ or ⅜ drive metric socket set, set of metric allen keys, jack and axle stands.

When replacing either the G78 or G76 sensors, it is fairly straightforward but there are a few points to watch out for, firstly, when releasing the electrical plug, they are quite fragile and the easiest way is to insert 2 small flat bladed screwdrivers underneath the catches on either side so that they clear the lugs on the sensor, the plug should then release itself.

Secondly, to remove the connecting rod ball joint from the sensor arm (parts 4 and 9 in the above image), it will be necessary to counterhold the flats of the ball joint spindle with a thin open ended spanner before undoing the securing nut, the pic below illustrates this










The 2 allen pins securing the sensors to mounting brackets are tight and a good quality allen key set is required.

When re-fitting the plugs, it is important that the rubber seal is located in the sensor socket fully before pushing the plug home. In the below pic, the grey seal is not fully located, it needs to be almost flush with the sensor socket turret, this can be done by gently easing it in with a small open ended spanner. When re-connecting the plug, some considerable force will be required before the lugs on the sensor locate in the holes in the 2 catches and this can take several attempts.










After replacing a sensor, clear any faults in module 55 and re-scan to see if the fault has cleared.

Whenever a sensor(s) has/have been replaced, it is important to get the headlamp alignment checked.


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## Tritium (Apr 25, 2011)

Excellent write up Steve. Very usefull detail. Off to the Knowledge base for this one I hope.

Apologies if I am wrong but " ..._both sensors are located on the left hand side of the car looking to the front_.." is wrong?

The diagram ( my car and Bentley manual) show looking at the car front grill the sensors are on the right ( nearside -UK)


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## Garth (Feb 7, 2012)

Nice.

I think this must be the only system that worked correctly on my car when I bought it but knowing my luck, it'll fail soon enough. At least I have some reference when it goes


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## steveupton (Mar 23, 2010)

Tritium said:


> Excellent write up Steve. Very usefull detail. Off to the Knowledge base for this one I hope.
> 
> Apologies if I am wrong but " ..._both sensors are located on the left hand side of the car looking to the front_.." is wrong?
> 
> The diagram ( my car and Bentley manual) show looking at the car front grill the sensors are on the right ( nearside -UK)


Thanks, it is a little confusing, think I might word this differently. I do mean nearside for RHD but tried to write it so owners of LHD TTs would read it OK.


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## SteveTDCi (Nov 10, 2009)

Thanks for this, I know the rear leveller has broken on ours and it's on my list of things to do, it was picked up on its last mot as an advisory,


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## John Stratton (Jun 20, 2010)

Brilliant write up , may have to use it one day , although hope not !!

Well done for taking the time to do this , I am sure one that will be used alot .

John


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## greyhound (Oct 27, 2011)

Nice one Steve! v.usefull


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