W203 C200 ELECTRICAL GREMLINS Aargh!!

[newdomainer]

Hi, I'm new to this forum and desperate for guidance on getting rid of the gremlins that are plaguing my C200 estate (2 litre petrol, automatic).

I realise that the only way to help identify the problem/s is to fully describe what is happening so I will post a comprehensive description of what I believe are at least two different electrical problems.

From what I have researched to date it is clear that I can spend a small fortune replacing various parts and sensors on a scattergun approach with no guarantee of success so I really hope someone here has experienced the same issues.


The first problem is one I have read about before; -

From cold start up, the engine starts and runs ok but then misfires (badly) after a few hundred yards - this is only cured by switching engine off & restarting - this may be repeated two or three times during first 2miles but will then run ok...

I'm aware that the misfire is just the engine management shutting down (probably 2) cylinders but I don't know why???
My best guess so far is maybe "Cat" problems causing bad exhaust gas reading or a faulty sensor giving a duff reading? - but once warm, the problem goes away!



The second problem is more serious because it can happen suddenly and everything electrical just dies and the engine runs at barely idle speed (seriously not the best thing when you're in the outside lane of the A3 doing 60+mph)

This sequence of "malfunctions" can happen at speed (i.e.on the A3!!) or it can happen when the vehicle is parked up & simply ticking over at idle.

Basically I get a fairly quick succession of "malfunction" messages:

I can't recall the exact order in which they appear but they are; -

Battery/alternator - visit workshop
Then ABS, ESP, SRS

Display reads 6 malfunctions

And no electrics work at all (incl. dashboard elements - speedo, rev counter, the indicators, the lights etc)
But the engine still runs (on idle) but won't rev much beyond tick-over

Next, I switch the engine off..

Switch ignition on again - and dash now reads "no malfunction" (no idea why it removes all the malfunction messages?)

The LIM light is illuminated on dash, as is low fuel (amber) light - despite gauge reading full! Also warning triangle, ABS, brake & BAS/ESP lights.
Red SRS light also comes on but goes out after a short while.

Unlike the 1st problem, this time I try to restart - and nothing! (Starter initially 'clunks' but doesn't turn).

After approx 10mins the car finally restarted!

Ran approx 1mile then fault codes all came back up... Went into limp mode, all electrics failed - engine running at idling speed & lumpy/kangaroos when attempting to drive it (in limp mode) -

So I pulled over and waited..... left it idling and after 2mins engine started to hunt - it was revving between (approx)800 & 1200 rpm on it's own accord (as if I was blipping the throttle twice a second) Then it stopped doing it after about 3minutes (as if it were running some kind of self testing / diagnostic.)
During this time the auto-gearbox wouldn't engage at all (i.e. locked in "park")

The display added a new message - "display defective - visit workshop"

THEN - after maybe 10mins? the engine revs freely again.... Gearbox engages but BAS/ESP light almost immediately came on and ESP switch appears disabled but all other electrics come back & car runs ok - no restriction on engine speed - revs up to red-line and even the gearbox kick-down works.


I have considered the following potential problems but I'm not convinced they are relevant, just a by-product but I could be wrong..

Many of the issues are symptomatic of a flat battery - but as soon as faults clear the lights etc work without any apparent sign of low power?
I've checked battery voltage and it's looking ok.
I've not checked the alternator output but I'm not experiencing any flat battery symptoms on these cold mornings so I can't imagine that the alternator is dodgy (but maybe I'm getting intermittent fault codes / readings from a faulty sensor or wiring fault?)

Also symptomatic of loose starter lead but again, as soon as fault clears car starts & runs fine so I don't think this is it either?

On another thread several members have advised that faulty brake light switches can cause ABS/ESP faults as can bad sensors and poor wheel alignment - I'll get my tracking checked this week as I need a pair of tyres anyway...

Probably not connected but I have also had bulb failure messages - I've noticed that headlight (n/s) works & then fails & comes back again on a random basis. Other lights all work when checked but then randomly drop out - e.g brake lights. but when I check the bulbs they're ok!

I'm hoping that my car isn't fit for the scrap heap.... for all it's gremlins, it's a lovely clean car and it's not a high miler....

Please help!!

 

[Stratman]

As you say, it does point at a battery on the way out. The off load voltage isn't that useful, it's much better to have a load test performed.

Before you do that, take it to an MB Dealer or better still a good MB specialist independent garage and have it put on the STAR diagnosis computicle. This will read all the fault codes stored in the car's microbrain.

You are correct in saying you can throw many expensive parts at it without result. A STAR session will be a good investment. Where are you based? We may be able to recommend a good indy.

Welcome to the forums by the way. If you stick around you will come across loads of useful information.


Edit:- You mentioned this happened on the A3. One of the most highly regarded indies is in Horndean. Prestige Car Service is run by a member on here, BlackC55. He will get to the bottom of this and won't rip you off. I live in South West London and make the trip down for all my servicing, and I'm by no means the furthest traveller to PCS.