Hi guys,

I have a question about my W124. Engine is the OM606, but I suspect this issue is simlar if not the same as the 2.5 turbo cars, since they have similar RPM/Klima/OVP wiring...

Last week my tachometer started to die randomly. At first only once in a while, now it is dead if the car has been just started. After say 3 - 5 miles or so, it will start to work again. Once you shut the car off, you have to drive it a while before it starts working again. Here is the weird part:

1 - the AC does not work, but before the tach starts working the AC will start. Lets say around 2-3 miles of driving.

2 - at around 3 miles or so, when the engine is under load, and you press the accelerator, it will start to work. When you let off the accelerator and the engine is not under load, the tach quickly dies.

3 - eventualy everything starts to work again... Then you shut the car off, and start it back up right away, and its dead again. Takes the same amount of time to revive itself as id did when the car was ice cold.

4 - Just replaced the RPM sensor. same issue. Looks like I have a spare sensor now...


Im thinking its either the KLIMA relay or the Overload protection relay. What do you guys think?

__________________
1977 Mercedes 300D

Have you simply tried tapping your cluster? The various gauges in the 124 I had would "wake-up" after a good hard tap on the bezel.

__________________
DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

I had same weird circumstances on my 350 SDL - screwed around with Klima for weeks, including new one ... would tap the relay area and the Klima and it would start working again.

Here's the story ....

Another OVP (Success) Story

__________________
George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg

The computer lab lady at our school drives a 95 C220, which might have a similar cluster, and I know that its instruments (Speedo and tach) haven't worked within 5 miles of startup for at least eight years now.... they just randomly wake up after a few miles of driving. Same issue?

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Purchased an OVP relay, I will update with any info. Thanks!

__________________
1977 Mercedes 300D

The OVP relay did the trick!. Purchased a new one, threw it in, and the ac and tach work great. Note to those that are in the same boat, the new style OVP relays have two more pins, and two fuses instead of one.

Thanks everyone!

__________________
1977 Mercedes 300D

Can ya take the old one apart?

Mine had some sealant around the base and cover, but popped open pretty easily once the sealant was removed ...

May be a simple fix, but don't know if they are still "relays" in the sense they have points in them ...

__________________
George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg

Where is the klima relay and how about a pic of the old one in-situ?

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2009 E320 Bluetec 117,000
1995 E300D 306,000 Sold
1996 Ford Taurus LX 130,000 Sold
1985 300TD Still 225,000 Sold
2016 Ford Fusion 24,900

Tried to take it apart, but it was sealed pretty well.

Location of OVP:

Behind the battery, to the right of 3 or 4 black relays. The OVP is a silver relay with 5 pins on the bottom and a red fuse on top. Pop the hood open to full open, then remove the trim behind the battery. No need to remove the battery.

NEW STYLE OVP:

The new style ovp has two fuses and 7 pins. Looks like an extra circuit for other applications. The extra pins don't seem to get used in the OM606, so don't sweat.

__________________
1977 Mercedes 300D

I have this exact same problem. Just brought home a 1995 E300 Diesel last night. Previous owner swears the ac and tach just started cutting out intermittently in the last week or so. I haven't seen them work yet, and I've been searching for hours now and running out to the car trying to find the problem.

Where is the best place to grab this OVP relay? I tried knocking it around a bit, but no luck. Will a dealer likely have it in stock? I'll do some more searching on the subject.

Thanks,
Todd

I fixed it. Ordered the OVP from Fastlane, popped it in this morning and had working ac and tach. Many thanks to the people of this forum!

Todd

My w123 does a similar thing. However the tach works only when the A/C is on. A/C works perfectly. I've been told to check the ground, but haven't done so yet.

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1982 240 D, 308,000 - 321,127 miles (sold)
1982 300 TD,166,500 - 226,000 miles
1998 E 320, 120,000 - 144,000 miles
2005 C 230 K, 26,000 - 77,000 miles (sold)

A/C works fine but the tach will sometimes not wake up till I get out of the drive way. No other issues yet.

Is this a sign of the OVP going bad and getting ready to fail? In other words, do I need to fix it now or can I put this on my to do list?

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Sent from an agnostic abacus

2014 C250 21,XXX my new DD ** 2013 GLK 350 18,000 Wife's new DD**

- With out god, life is everything.
- God is an ever receding pocket of scientific ignorance that's getting smaller and smaller as time moves on..." Neil DeGrasse Tyson
- You can pray for me, I'll think for you.
- When you understand why you dismiss all the other possible gods, you will understand why I dismiss yours.

My AC would work fine but the tach was mostly inop. OVP fixed it......

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

Most likely OVP relay. Intermittant is a normal failure mode.

__________________

Gone to the dark side

- Jeff