W124 ECU problem?

[Lews]

I am new to this site so hello to all.

I recently bought a Merc coup W124 which had the sds light on the dash and was not running perfectly on all cylinders. Upon reading and testing I found out it was one of the coil packs which I changed and the car now runs and drives perfect. This has also got rid of the sds light however, I now have no headlamps, wipers and have found that the electric window and sunroof work intermittently. Could this be due to a faulty ECU? With the engine off and the ignition on I can hear quite a deep humming sound coming from the ECU, is this normal?

Any help on this will be appreciated.

Lews.

 

[grober]

The ecu should be silent. There are 2 or 3 relays beside the ECU which might be humming a bit. THE ECU IS LOCATED BEHIND THE BATTERY OF COURSE! The OVP ( OVER VOLTAGE PROTECTION RELAY) and the FPR fuel pump relay. You could try removing each in turn or giving them a tap to see if the humming stops--the car won't run of course. The other problems are probably fuse or relay related. There's a big relay in the relay box behind the fuse box called the convenience relay which might be faulty. relay H The fuse holders/fuses get surface corrosion which results in intermittant contact. A quick clean up is often all that's required.

 

[kth286]

Yes - highly likely to be the fuses.

Give each one a good turn in it's holder.

Change the ones that obviously are bad.

 

[Lews]

The car was standing for a few months, as there were no electrical problems before the coil fault I hope this will do the trick. Many thanks for the help.

Lew

 

[Lews]

Ok so I have changed all the fuses and had a look at the relay which has not got any surface rust. Good news is everything electrical now works albeit the headlights, still? I should say i can get high beam on the headlamps.

 

[grober]

Could be the headlight dip switch which is part of the combination switch on the steering column or a problem with the large relay K (depicted in the diagram as 3 relays) the exterior lamp failure monitoring unit. Sometimes if you wiggle the stalk a bit you can get it to "sort of" make contact now and again. If you can its a pretty sure sign your problem is with the combination stalk.

 

[Ted]

Worth just checking the bulbs before getting deeper into it.

 

[imadoofus]

Incidentally, my coil packs needing replacement was the first sign that my loom was on the way out.

 

[imbck666]

Loom is the correct problem.. main cause of that is age.
ECu is certainly silent and should not cause any sort of sound such as humming.

 

[mercedeslover]

Hello there. I have not had that problem, but what I have done is take out all the ecu's and cleaned the connections/plugs. Also I have cleaned all the connections in the engine bay & the earths. Fuse box next. Hope this helps.