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ABS and PSM warning lights on AGAIN

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The last time this hapened it corrected itself.

Now it has become real strange.

If I put my lights on, the ABS and PSM warning lights light up immediatly.

If I leave the light switch in the off position, the front left headlamp lights up when I put my foot on the break light. This is annoying as it is winking at everyone every time I put my foot on the breaks. With the light switch in the off position the ABS and PSM lights don;t light up even though the fron headlamp lights with the footbreak.

The rear break lamps are working fine though.

Any ideas?

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Sounds like the old bad earth chestnut again. You would see this on old F*rd Escorts from time to time. I suggest it is in the left rear cluster, as it is lighting the front left lamp. (Sidelight, I presume??)

Consider the following:

From the fuse, power goes through the brake light switch, through the lamp, then to earth (and back to the neg terminal of the battery. From the tail-light cluster, all the lamps in the cluster have their earth side joined in a bus bar, then a single (brown) wire takes it to earth.

If this earth becomes a high resistance path, (loose wire or corrosion or something) the current now flows from fuse, brake switch, brake lamp, earth bus bar (NOT to earth at this point) tail/sidelight, back up the wire to the sidelight at the front of the car and down to earth there. This explains why the front sidelight will illuminate.

When you switch the sidelights on, again the sidelight can't find its earth in the rear cluster, so this time the current backfeeds through the brake lamp, up to the ABS/PSM module, whereby it will cause the module to think there's a fault (The ABS/PSM module monitors whether the brakes are being pressed from the brake lights, hence the module is downstream of the switch, and will be affected by the backfeed)

Conclusion, check the resistance of the brown wire in the cluster to a metal part of the body, in the left rear. (but I would check both to be safe)


Newcastle, UK

(*Nearly* Capital of Culture 2008 - Scouser will understand this!!)

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Thanks for that detailed synopsis 0586slb.

You said check the brown wire in the cluster to ground.

Which cluster and where will I find it?

Since your in the UK, would be good if we could chat on the phone ;)


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