W202 speedometer issue - Searched but cannot find answer - PeachParts Mercedes-Benz Forum

hk20000 · #1 01-28-2007, 03:34 AM

hello guys,

I'm new to this forum, I just bought a C220 W202 and I've been searching up and down to find a diagnostic of my problem:

- I have no speedometer reading
- My odometer does not advance
- my ABS is not doing anything when I jam on the brake pedal.
- My CEL and ABS lights are both non-existent.... you turn the key to ON from OFF and you still will not see it.
- the car drives perfectly normal - shifts through all gears and accelerates swiftly
- sometimes idling below 500 RPM and stutters, but it never stalls.

From reading on other speedo threads on the board my guess is my speed sensor because it would be strange to have the odometer and speedometer on my gauge cluster go out at the same time.

but then, others who have lost their speed sensor seems to not get proper gear shift....Yet I do have shifting in very typical way.

Can someone try to narrow down this problem for me? The front speed sensors should only do the ABS circuit and not the speedo/odometer circuit right? Do you think I'm on the right track to start checking the rear differential speed sensor?

thanks.

shandy · #2 01-28-2007, 05:21 PM

First check your overload relay, it's the tall silver relay in the Ecu compartment at the passenger side rear of the engine bay, there are one or two fuses on top of it check if they have blown.
If the fuses are ok then the relay itself may be faulty and should be replaced, the overload relays fitted to cars like yours were part of a bad batch and most are faulty now,mine was. They usually cause faults in the abs system, poor idling or stalling so it sounds like your culprit.

hk20000 · #3 01-29-2007, 03:56 AM

the fuse looks ok.... Got any tutorial online to the relay?

But that aside what's the best course of action to get my speedometer back? I managed to pull out my gauge cluster with a captain hook style hook I got from the yards a while back..... replaced the ABS/CEL bulb with ones that are in the blank blocks, now the ABS light is on yet the CEL is not. What could have caused this? I tried a handful of bulbs on that slot and I still can't get a check engine light to come on....

wbrian63 · #4 01-29-2007, 07:51 AM

You say that the ABS light is "on" - do you mean it's on all the time, or that it comes on during the bulb test when you switch the key to on just prior to starting.

If the ABS light stays on after starting the motor, that indicates a fault in that system - computer scan for codes required to further chase the problem.

You should see the CEL as part of the bulb test mentioned above. If you don't check the bulb again by swapping with a known good one. If it still doesn't light then the problem is way beyond my ability to suggest a course of action.

If you just purchased the car and the ABS bulb was out, it might indicate tampering prior to sale to hide a known problem - or did this stuff start after you bought the car?

This is a BIG hint to anyone purchasing a used car. If all of the warning lights don't light up during the bulb test, get the seller to fix the bulbs first. If they stammer or avoid the issue - walk away from the car.

Speedo and odometer work from the same feed - if the feed is bad, both will cease to work.

hk20000 · #5 01-29-2007, 09:25 AM

thanks,

yeah I'm quite sure it's a scammer thing, but what can I do about it...I found the car at the auction. It does drive and go pretty well aside from the maybe 1 out of 15 times stuttering idle. And I'm happy for what I've paid for it.

When I said the ABS bulb is on it's on the whole time when the engine is started - ABS is faulty. But I'd imagine that is because my speed "feed" from the differential is bad. no speed feed from the rear = no ABS, right?

makes no sense how come the CEL does not light up even after replacing the bulbs though.... faulty connection on the cluster maybe? Everything else comes on properly.

I guess I'll go grab a new VSS and swap it out and see what happens with my speed and maybe my ABS fault light.

What stumps me here is that my car "seems to" know how fast it is going because it is shifting gears normally. But if it knows how fast it is going (Assuming faulty gauge instead of faulty VSS) then the ABS is a whole different can of worm.....

hk20000 · #6 01-29-2007, 01:20 PM

I called up Mercedes Benz and they say that sensor in the diff is not a speed sensor "that's an ABS sensor sir" and now I'm totally messed in the head

what?

so where is the speed sensor for this stupid car!!!!

the parts catalog says it's a "sender unit" but it doesn't say jack about what its use is.....

anyone?

shandy · #7 01-29-2007, 06:25 PM

I've got the same car as you,UK version,the signal for the speedo comes from the ABS sensors as an average of the signal from the three sensors (one on each front wheel and one on the final drive unit ), if any one of the sensors is faulty there is no signal to the speedo. Check all wiring connections then each ABS sensor in turn.

hk20000 · #8 01-30-2007, 01:31 AM

I have solved the mystery.

as weird as it sounds ALL my problems came from the OVP..... what the ****

the OVP simply cut out my engine check light and speedo making it look as though the speedo itself is a lone problem.... then together with other symptoms of the OVP I had stalling idle (<500rpm speed) and ABS light.

one swift re and re of the OVP later and it all came back online....

what a stupid design...

TimFreeh · #9 01-30-2007, 08:05 AM

Quote:

Originally Posted by hk20000

what a stupid design...

The use of an over voltage protection relay to protect very expensive electronic components from voltage spikes is not a stupid design.

I'm glad you were able to fix your all your problems with a $100 OVP relay - and I'm glad my cars have OVP relays engineered into the electrical systems.

blackmercedes · #10 01-30-2007, 09:18 AM

Most cars do not, and boosting them can result in a massive bill for electronic parts. When I owned an auto electronics store, boosting a car was cause for immediate dismissal, thanks to the problem. We had to replace a few very expensive modules beofre we learned our lesson. OVP's can be a very good thing indeed.

hk20000 · #11 01-30-2007, 10:52 AM

well doesn't change the fact that it doesn't have a clear indication of OVP failure not a stupid design.

there should be an OVP failure LED or something on the dash or even on the module itself for much easier diagnostic. How hard could it be to have a circuit checker in the module and some LEDs?

shandy · #12 01-30-2007, 04:40 PM

A thanks for the heads-up on the OVP relay would have been nice , but that's the way of forums , no one talks about the successful outcomes.
I tend to agree with you about OVP failure indicator, but it would have been better if MB had done a recall on all affected vehicles ( look at your faulty OVP, its a Seimens isn't it ???, part of a faulty batch and they are all going to fail eventually).
Anyway glad you got it sorted.
George.

hk20000 · #13 01-30-2007, 06:46 PM

I'm thankful of the help, of course, that goes without saying.

It's the design that IMO is a stupidest piece of designed electronic equipment on a car I've seen. Nothing to do with anyone here who had been of great help and warm welcome.

dwfinc2000 · #14 10-30-2008, 10:56 AM

Thank you Hk20000 for posting this problem, you saved me hundred of dollars, from not having to take this car to the dealership! The OVP relay fuse was blown, all problems on my 1994 c220 solved! Thankyou Shandy for posting comments as well, and others like cyberwolf60 for asking questions also. This forum rocks!

Islandw202 · #15 03-04-2024, 03:13 PM

Hey OP! @hk20000 and others, did the lights that were not working reappear after the OVP was replaced ?

TIA 🙏🙏🙏