Faulty Electrics

[leblanc]

I have searched the forum and still not found an answer to my problem C250td.
X reg.
It began by showing most warning lights then got worse by pulling back to the point where I thought the engine was going to cut out. This is sometimes accompanied by much gearbox activity. Restarting is a temporary fix.
My local indie cannot pinpoint the fault which of course does not show up when he looks at it.
The only possibility he found was some corrosion in a small multi-pin socket which plugs into a small black box in the fuse compartment on the passenger side. This was difficult to clean effectively and it seems part of the wiring loom.
It locates on small fragile pins on a PCB within the black box. There is a relay and lots of connections to the box besides this one but they seem clean.

Does anybody know what this is (the black box) and would it produce the faults I am experiencing? What would the remedy be please?

 

[anyweb]

check your OVP relay, its the one with a FUSE on the top

it's common for the internals on that to get loose connections (solder) or for the legs to fail to make correct contact

now, it's possible that your diesel doesnt have one of these, but if it does, check it

 

[leblanc]

Thanks for the quick response.
I had read about the OVP relay but cannot find one on my car.
There are fuses near the battery in the boot but no relay. Anywhere else I should look?

 

[anyweb]

on my C220 (petrol) its right beside the ECU under the bonnet,

if yours doesnt have one then maybe that's a diesel thing, i honestly don't know.

hopefully someone here will know

cheers
anyweb

 

[leblanc]

Thank you again but still unable to find OVP relay if there is one on the diesel.
I can only see a connector block next to the ECU.
There is some other electrical device under the washer bottle but doesn't look like a relay.

So, if anyone could point me in the right direction I would be most grateful as the reported problem has not gone away.
I'm still suspicious of the black box next to the diagnostics socket which as I said had some green corrosion around one of its connectors. The indie cleaned it up best possible but problem not gone away. As it contains a printed circuit board I wonder if corrosion has spread inside although it looks clean enough.
NB. This box does have a black relay with four blade terminals on it but no fuse mounted on the relay. There are independent fuses also mounted on the box. These are all clean.

Any help gratefully received.

 

[television]

The OVP reley is 128 in the link if you have one , other than that it will be the MAF

http://www.detali.ru/cat/oem_mb2.as...GM=717.460&CT=F&cat=44V&SID=54&SGR=045&SGN=03

 

[leblanc]

Thanks for your help Malcolm. However, on following the thread "How to clean your MAF", I find that according to reply no.67 dated 15/4/07 from 123K my C250td does not have one.
On inspection this seems to be the case.
Now, this leaves the OVP which I still cannot locate. The diagram on the link points vaguely to somewhere under the bonnet.
Do I need to take the fuse box out to see it or is it more obvious?

Thanks
Mike

 

[anyweb]

on my car, the ecu is covered with a protective black piece of plastic covering the whole corner area and ecu, the ovp is right beside it and you can't miss it as it has a see through top where you can see a fuse on top of the relay.

on my left hand drive car its on the left hand side of my car towards the rear (the opposite side of the fuse box), on your right hand drive car it may be located on the other side.

cheers
anyweb

 

[anyweb]

you can see the cover i'm talking about here
top left of this photo - http://www.niallbrady.com/mycar/c220/car_interior/july_2006 097.html ), lift this plastic covering and you'll see the ECU and the ovp is right beside it

 

[leblanc]

You're quite right anyweb, my car has a large cover over the ECU on the left hand side.
(passenger side on right hand drive). No sign of a see through top or relay though.
I'll photograph it tomorrow for clarification in case I'm missing something.

Mike

 

[leblanc]

Good morning,

I have attached a picture of the ECU (top removed). The only relay I can see is the small black one bottom left.
This is plugged into the unit where the corrosion was spotted by the indie.
The area where the corrosion occurred was on the right hand side of the unit.
It is a small multi pin plug just above the diagnostics socket. This was green, now cleaned

Hope this clarifies and helps clear up the OVP location if there is one.
If not, any ideas where I go from here please.

Regards
Mike

 

[television]

What are the next 3 numbers after 202 on you VIN number 128 or 188

 

[leblanc]

It's 202128

Mike

 

[leblanc]

Now getting desperate.
Warning lights still keep coming on. There does not seem to be any regular pattern.
Yesterday, had all brake warnings on. ie. BAS, ABS, pad wear, handbrake. All reset on restart.
Today, had most others on and no speedo or rev counter and intermittent coolant temperature gauge.
Drove home, took the cover off the ECU compartment (engine still running and warning lights still on etc.) Wriggled wires and plugs while an assistant observed panel.
At one point, the temp gauge went ballistic and observer (wife) heard a relay under the dash somewhere, clicking on on off, so thought I had found something.
Switched off and restarted, No more lights and temperature gauge reading correctly but unable to reproduce the fault.
Now think it may have been coincidence that my wriggling of wires and connectors sent the temp gauge into spasm but I really do not know now.
I have examined cables and plug and sockets around the area but all looks normal.

Can any one suggest what my next move should be please?

 

[television]

Go to Maplins get some non drying switch cleaner.

Every thing in your fuse boxes unplugs, thats all the ECUs and relays, clean off all the pins on the units then spray them all with the cleaner.

There are now two modified lids for these boxes to keep the moisture out

 

[leblanc]

Thanks for the suggestion Malcolm. I have indeed been using a high quality switch cleaner (Electrolube) to treat fuses and holders.
I'm obviously missing something.
Although I have some electronics experience, my knowledge of auto electronics is almost zero.
Can the connectors be taken off the ECUs without upsetting them and putting up fault codes?
So far I have only dared to take out fuses and replace or clean the ones that looked in any way suspicious.
Do I disconnect the battery or anything or take any other precautions before unplugging?

Thanks again

Mike

 

[BlackC55]

Stop looking you dont have an OVP.

This could be a voltage issue. Is the battery good?

 

[leblanc]

I "think" the battery is good. That is to say is reads about 12.4v in the morning before starting then 13.8v with engine running.
The symptoms do not occur immediately but happen randomly during normal running.
I drove the car 40 or so miles last week without a hitch. Today I got the warning lights and no speedo/rev counter after only a couple of miles.
Does this still possibly point to the battery?
I don't know how old it is, but I have had the car for nearly two years and I haven't changed it.
Just to complete the story, I didn't use the car for about two months earlier in the year owing to illness. My wife did start and run the car a few times for me.
When I began to drive again, I noticed the warning lights flash very occasionally but they always reset on restarting.
I mentioned this to the local indie when he did an ATF change for me.
His diagnostics did record a low voltage occurrence but he did no seem to place any significance on this as when he road tested the car, no warning lights showed.

I'm beginning to wonder now about the battery. May I ask for your thoughts again before I buy one please? (I've just finished removing cleaning and replacing relays and all fuses I could see, they all looked clean).

Thanks for your help
Mike

 

[Bolide]

Reading the last page of posts I immediately thought battery! It could also be a bad regulator allowing voltage variations. AFAIK this is what the OVP is designed to protect against

Is the car parked in the open or under cover?

Nick Froome
www.w124.co.uk

 

[leblanc]

Thanks for your reply Nick.
The car is parked in the open.
Further to this and hopefully unrelated, I had water ingress into the heater blower and passenger foot well just after I bought the car. I found the culprit (blocked drain) and rectified. The blower has worked fine ever since but I did wonder in view of the amount of rain we've had if something could have got damp. I can't see any obvious signs though.

Can you suggest any common places to look?

Mike