Cruise Control Symptoms: Please Diagnose - PeachParts Mercedes-Benz Forum

shertex · #1 01-11-2008, 08:31 AM

With respect to a malfunctioning cruise control, my understanding is that, if the switch or actuator is bad, the cruise control simply won't work.

My symptoms are as follows: when cruise control is engaged, the car lurches intermittently: speeds up, slows down, speeds up, slows down, OR it gradually accelerates and then slows down. This happens whether I push lever up (accelerate position) or pull in (set current speed position). Whenever I disengage the CC, it successfully disengages.

From everything I've read, it seems like a VIRTUAL CERTAINTY that I have a bad amp that needs to be repaired or replaced.

Do you agree?

Thanks.

donbryce · #2 01-11-2008, 11:12 AM

I agree. Re-solder the PCB, or send it to a rebuilder. I've seen rebuilt units on EBay for around $140.00 + shipping.

cdplayer · #3 01-12-2008, 10:44 PM

Not wanting to step on any toes here, but I read a post in this forum, way back, that described the ill effect using the wrong brand of brake light bulbs had on the Mercedes cruise control system.

Use only Oshram or Bosch brand bulbs. Just plugging in an 1157 bulb from Auto Zone or Pep Boys will cause the cruise to shut down. These bulbs(1157) are not designed to supply a critical ground to the cruise control circut.
This seems rather odd. But after I replaced a burned out brake light with one I had on hand, my cruise began acting up. Lurching,not activating,accelerating without leveling off, etc. I didn't realize the bulb cause until I read the post. After replacing the "new" bulb with a Oshram, I had cruise control again.

shertex · #4 01-13-2008, 05:29 AM

It's hard to imagine the brand of bulbs could make a difference. At any rate, I'm not an EE, so who knows? I do have a few "off brand" bulbs in there. But, in my case, they were in there for some time (as in years) with cruise control working fine. From those who claim bulbs make a difference, my impression is that the malfunction woudl be immediate and consistent.

dpetryk · #5 01-13-2008, 08:40 AM

It's not the bulb. Your amp is the problem. Bulbs will cause a problem when there is a crack in the filament. Many bulbs work with cracked filaments and you don't know there is a problem until they fail completely. However when the bub is not lit vibration causes a high resistance / intermittent resistance path to ground to the cruise control amp and can make it twitchy. And another thing - bulb brands do not matter as long as the right wattage is used.

crhenkel · #6 01-14-2008, 12:01 AM

I would bet the farm, if I owned it, that the amp is bad, seen it many times, actually my 16v is doing it right now. Resloder the connections yourself and it will work again most every time, take your time, use a fine point solder iron and it will be all good. Even after a rebuild shop does the work for the tune of $150 or more, they can go bad again, ask me how I know. i have several in the shop and I solder them up as needed. I have done it 4 or 5 times and it fixed the amp each time. Good luck, dont be afraid of the task, the amp is already bad, it cant really get "more bad". Never heard the bulb issue.

jaybeckham · #7 03-31-2008, 05:05 PM

I may have the Amp problem some are discussing. Can someone tell me where the Amp is located? I do a lot of electronics work and have fixed a lot of problems with re-soldering.

Thanks

Jay Beckham
Berkeley Springs, WV

BenzGang · #8 03-31-2008, 05:57 PM

i have the same problems with mine too, sometimes it works fine, other time nahh

compress ignite · #9 03-31-2008, 07:12 PM

Jay,
Which model "Mercedes"(We may be able to help you with that)

(If the Honda has a "Cruise Amp",it is not allowed to go "Bad")
[If it does someone in Edo commits ritual suicide,for shaming the company]

BenzGang,

The "Picture" is your CC amp.[N4] (under dash) (The pedal in the picture is your
brake pedal)
The "Drawing" is the CC relay .[K12/1] (the tray in the foreground should be the battery tray)