weisdaclick

A little help required here please.

My Tempomat cruise control on my 1993 W124 320CE keeps on intermittently switching off.

Its one of the best parts of the car so its annoying to keep having to set it again.

This seems to happen at random and at any speed and I believe its getting worse - that is it is switching off more and more often.

All ideas & comments gleefully accepted .

shdoug

How is your throttle actuator wiring? The wires are biodegradable, and the part is around $400 rebuilt on E-bay.

PaulX608

Another thing to check is your brake light switch. A loose or badly worn brake light switch could cause this type of random deactivation.

shdoug

Good Call! A much cheaper possibility as well.

Bartman

Likely needs a control unit, could start with brake light switch as they are cheap enough, but not a common failure on 124's as on late cars. Regards, Bart

jgajito

It could be anything in the fuel distribution system as well. MAF Sensor, a vacuum leak, electric short. It may even be a bad column switch or maybe just worn. Are you in a dusty environment? Sand/Dust can cause contact damage around the steering area due to open windows especially aroung the area of the turn signal switch and the cruise control.

-J

carlson03

I also had many problems with my cruise control...one being it would just shut off. I resoldered some points on the cruise control amp, seems to be working much better now.

weisdaclick

Hmmm quite a bit to look at there.

I'll check the throttle wiring and column switch. Is the cruise control unit built into the throttle body?

carlson03: Where is the cruise control amp you soldered?

Bigpete123

look this issue up on mercedesshop.com. Many people have found that you just need to pull the cruise control amp and re-solder all of the contact points, just like carlson said.

My understanding is that the amp is mounted somewhere near the steering column or under the dash near the driver's feet.

Chappy

What size wheels and tires are you running? This may also have an effect on the proper operation.

carlson03

yeah, the amp is located just under the steering column...there are plenty of help guides on how to do it, but if you can't locate one, I can tell you how to do it.
btw...when I opened the amp, there was some sort of coating that mine had, looked like to protect the circuits...not sure, but I used paint stripper to remove it, then I was able to start the soldering.
I spent about 30 minutes, just going over most of the points, adding solder to joints that needed it. If you have any soldering experience, and a good soldering tip, should be an easy fix, hopefully.

mdsjsb

I had the same type of problem where it worked at times and then just stopped working, later, minutes, hours, days it would be ok again. Common thread seemed to be the ambient temp display would go blank too. It was not and still is not showing correct temps but it seemed to go blank at the same time. I then had a coolant hose failure, not really the hose but a "Y" type of hard plastic hose connection on the left firewall that had a small leak. It got worst and finally failed. I changed it and noticed at that point that a couple of wires ran directly under it, I surmise, could be the ambient temp wire and the cruise control wires. Anyway leak fixed, no more cruise problems and the ambient temp displays, albeit wrong temps, it generally displays about 127, goes up to the 130's and sometimes goes down to the high teens. Just "AWAG" as a possible solution.
Good luck

weisdaclick

I am running 215/55/16's at the rear and 205/50/16's at the front which I'm sure are ok.

I have had the tyre problem before, I think I had a pair of 205/50/16's so I put them on the front.

After that the cruise would not work above around 40mph, took me a few hours to work out what was wrong.

weisdaclick

I'll get under that column and try to find the amp, I'm not bad with a soldering iron so hopefully I'll be ok.

Thanks for all the help with this issue.

Hank3rd

I have been trying to troubleshoot my cruise. It started out working intermittently and then I took out and resoldered the amp and it stopped working altogether. I bought two used replacement units that were tested and it still did not work. Later on, my CEL came on and it was for the idle and found my actuator/throttle body may be going bad. My INDY replaced with a used unit and the idle problem went away and he cannot find the problem with the cruise. I then replaced the brake switch and still no go. All tires are the same size/pressure.

Any ideas?

Hank