benja

My '90 C4 coupe has developed some really odd electrical issues in the last couple of weeks and I haven't got a clue where to start?

Late last year it started to develop an intermittent transmission warning light which would come on for no reason, and could be reset by switching the ignition on and off. That may or may not be related.

The main issue has started in the last couple of weeks. The car was left for about 5 weeks outside for the beginning of the year, and to be fair its been biblically wet which may mean some damp ingress.

First symptom was that although the car started strongly after a long rest, the headlights refused to come on and the brake pedal was not working much at all (I'm guessing servo?). After 20 yards, everything started working again.

Then today (my next journey - a couple of weeks later), the car was fine, except the speedo didn't work for the first 10 minutes. Then after a brief stop, the indicators and windows wouldn't work, but the speedo was fine. Then during the journey back the brake pedal went again, headlights didn't work (sidelights were fine), indicators came back and windows still out.

It's really odd? Could it be a shot battery after not moving for 5 weeks meaning low voltage confusion? Damp in somewhere it shouldn't be? ECU / DME on the way out?

Any advice / suggestions would be really appreciated....

Earlydays

Some thoughts:
1) Check your interior carpets to see if they are wet....water may have gotten to your DME
2) Bad ground wire on your battery
3) Check for dampness under the hood, particularly under the carpet...water can get in past the seals and if it has been sitting a long time everything can be very damp

boxsey911

Well, if it was outside for 5 weeks and not on a trickle charger the battery will be just about empty. I would take it off and charge it up as a first step. If that doesn't do anything, check that it is charging when on the car - you should see at least 13.4 V across the battery terminals when idling.

robt964

Given the intermittentness, my money is on the ground points. The blade terminals that hold the the fuses in the fuse box can also fur up - mine did which prevented the ECU from sparking up. Bad connections can frequently still show a voltage but won't flow much current.

benja

I've only just managed to get the car to check it (you can see why she sat unused for January!).

Nothing in the carpets damp-wise, though I have the usual condensation problem.

Battery is giving 12.0V without the engine running and 14.6V with it running, which means the alternator seems to be working. But a knackered battery?