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Old 27th October 2019, 16:28   #1
graham clarke
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Default rear fogs

MOT fail: rear fogs warning light absent but the bulbs are working, yellow bulb fail light comes on, then yellow icon showing fog light fail, the bulbs are still working. I have checked the bulbs and holders and all looks good, I have tried the 30 mins battery off reset.
Any suggestions please?
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Old 27th October 2019, 19:49   #2
sewerman
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Are they led builds ? If so replace with ordinary and see what happens

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Old 27th October 2019, 21:04   #3
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Quote:
Originally Posted by sewerman View Post
Are they led builds ? If so replace with ordinary and see what happens
If they are not Canbus compliant LED bulbs the system doesn't recognise them.
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Old 27th October 2019, 21:10   #4
graham clarke
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Default fog lights

No, 'ordinary' bulbs.
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Old 27th October 2019, 22:42   #5
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Hi Graham,

This could be a fault on the K-bus between the LSM (Lighting Switch Module), which controls the rear fog lamps, and the IPK (Instrument Pack) which displays the bulb failure warning.

You might like to check that the connector at the rear of the LSM hasn't been disturbed.

Simon
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Old 27th October 2019, 23:27   #6
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Possibly a transistor failure in the LSM, the bulb monitoring system works by keeping a low voltage that goes down each lighting circuit through the bulb and to one leg of the transistor monitoring that circuit.
Failure to register the voltage to that leg of the transistor will cause the bulb warning system to activate.

If you have access to a replacement one from another car try it and if the light goes out the LSM is faulty.

Russ
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