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6.4 - Lamp Modules ( )

6.4.1 - Overview ( )

The lamp modules give problems on all older XJ40s.

The first thing to note is that these modules' concern is not only monitoring bulb failures, but also switching of the bulbs themselves. Each lamp module gets signals from the various devices like headlamp switch, brake light switch, indicator switch etc. These signals trigger relays in the modules, which switch voltage to the bulbs.

An in-built circuit checks the resistance of the bulbs, if anything abnormal is measured, it grounds one of the lines to the VCM and the warning signal in the instrument panel lights up.

Two different bulb failure signals are delivered by each module:

- Indicator failure (pink)
- all others (pink/grey).

When the VCM receives the indicator failure signal it changes the frequency of the audible signal, and flashing arrow on the dash when the indicators are working.

6.4.2 - Quick Check List ( Brett Gadzinsky,  )

Bulb Failure Modules (BFMs) have a reputation of maddening failures on XJ40s, but there are things to check before jumping in replacing or repairing the modules.

If you have a bulb fail alarm, check all the bulbs, the headlights, high and low beams, and driving lights, the turn signal, side marker, brake lights, backup lights, front and rear fog lights. Even if you don't have front fog lights, the shorting plug needs to be in the connector for the fog lights.

Its best to use plated base bulbs, not brass base bulbs, as the sockets are plated, and using dissimilar metals in a hot moist environment is sure to cause corrosion problems over time. The brand of the bulbs is not important, but the wattage is.

On some cars, the bulbs can get loose in their sockets. Make sure the prongs at the bottom are forcing the bulbs lightly into their sockets.

If all the bulbs are good, and they are all working, and you still have the alarm, you need to remove the bulb fail modules from the car and resolder the bad solder joints inside.

6.4.3 - Module Repairs ( Brett Gadzinsky,  December 15, 2001 )

The modules are at each corner of the car, close to the lights. Trace the wires from the lights to the module. The modules have a metal cover over a plastic base plate. You need to straighten the bent tabs on the cover, then pull the cover off.

Inside you will find a main board, and maybe a smaller sub board that mounts on its connectors. The main board is held onto the base by four Phillips head screws at each corner. Remove the screws and then the main board.
Solder problem spots are the connectors between the sub board and the main solder both the main board pins and the sub board pins. A very close inspection of the solder joints may show rings around the joint where the solder cracked. Also resolder the relay joints on the main board.

Most of the joints on the little parts will be ok. Also check the relays inside...they operate the lights. If the module looks dirty inside, the relay contacts may also be dirty, and that will cause problems also.

The newer the car, the less problems you are likely to have inside the bulb fail modules.


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