W208 230k - random (near) total electrical failures

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MercedAde

New Member
Joined
Feb 28, 2008
Messages
3
Location
Manchester
Car
260e
Hi all - it's been quite a few years since I was here, but I hope there's some brains to pick.

My '99 CLK has the worst kind of electrical fault - a randomly occurring, intermittent cut out that I can't replicate or force, and doesn't appear to have any specific conditions associated with it.

I noticed a few weeks ago that it wouldn't always start when I got in it. The full selection of dashlights would light up when they key is in position 2, but turn it and absolutely nothing would happen. The dash lights would all go out except the SRS light. If I locked the car and then unlocked it, it seemed to work normally. However, I think this was possibly a red-herring, but maybe others will think differently. I think at the time I convinced myself that it was an immobiliser.

Then was I driving a few days ago, doing a steady 30 mph, when it just totally, electrically died (apart from the radio and the dashlights). Just like someone had turned it off. I coasted for about 3 seconds, trying to signal that I was pulling over - but didn't even have any indicators. Hazards still worked. Whilst coasting, in gear, I didn't do anything - it just sprang back to life. Drove on as if nothing had happened.

Didn't happen again for a few days, then it happened yesterday. Only this time, it didn't restart. Coasted to a stop (same electrical systems - radio fine, hazards fine, everything else dead). Tried locking and unlocking the car, tried wiggling/shuffling through P/N/R/D, tried removing the key and retrying - but nothing. Sometimes I would get no dashlights at all except the SRS light, sometimes I would get all the lights as normal, but no start. The roof was down, and sometimes I thought I could hear the fuel pump running on the times when the dashlights illuminated, but no joy. Then, after about 90 seconds or so (which is a REALLY long time!) it just randomly started again.

Battery voltage is mega healthy, and the car - once it agrees to crank - starts beautifully. No struggles to fire or anything.

Questions:

I wonder if this is a dodgy earth connection? If so, where should I start?

The random cut outs whilst driving felt like an immobiliser cutting in - the fact that it lost all electrics, rather than losing just engine power, suggested something turning off. But what?

Anything else I could check diagnostically?

Thanks all
 
Possibly the ignition switch itself failing, which I think Mercedes call EWS? Things like the radio, hazards and sidelights/dash illumination will all work if the ignition switch is off. Indicators, engine and almost all other electrics will not work with the ignition in the off position.

Unfortunately, I have no idea how to test that reliably. A code reader might help, and wiggling/turning the ignition key very slightly when you get the fault might point to a confirmation of the switch itself.

Martin.
 
Back in the day, when a car wouldn't start (ie all lights on, but turning the key resulted in all lights going off and nothing happening) a common cause was poor battery connections giving a high resistance. So a cheap check is to make sure the battery connections are solid. In this case it probably doesn't explain the other "features" of your issue, but worth a look.
 
If it is the EIS, give these a call ReplacementMercedesKeys - Mercedes EIS Repair Specialists I have used them for a replacement key before

Well, I got in touch, but he seemed pretty determined that it wasn't the EIS. He reckoned it couldn't be, because it wouldn't shut the car down whilst driving. So perhaps I'm back to trying to look at earths etc.

I really hate random electrical faults.
 

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