cruise control...DANG it! - PeachParts Mercedes-Benz Forum

blankenship · #1 10-27-2009, 10:41 PM

yep. another cruise control post.

i'm trying to diagnose why mine's not working.
i seem to remember diagnosing one on a prior step-by-step "troubleshooting" article on the mbz.org site, but i'll be darned if i can find the article now.

anywho: i've got NO cruise function. nothing.
it's the 14-pin system on my '85 wagon.

i've swapped both the amp and the motor with an amp and motor [untested, of course] from a low-mileage junkyard find, to no avail.

instead of just assuming the amp is bad, can someone provide a "how-to" on testing for the proper function of the other components of the system?
shouldn't you be able to test for voltage on certain wires (like coming from the stalk control and leading to the motor) to know (by process of elimination) where the problem lies?

help would certainly be appreciated.

sasquatchgeoff · #2 10-28-2009, 01:19 AM

I don't have a copy of yours, but my FSM has an in-depth method for troubleshooting - with a MB test device of course. There are a zillion posts that contain links of various worth detailing the process for the average shade-tree, but I think you are on the right track.

You did not mention the difference in behavior for the two sets of components (JY vs "stock") - do you have any behavior to post? Or is it just plain dead?

There are three main components - the cruise amp, the hall sensor (if yours has one - somehow attached to the speedo) and the cruise actuator (the motor that drives the accelerator linkage under the hood.

Nine times out of ten it is a shot cruise amp. They are a pricey rebuild ($200-300). Ironically enough, sometimes it is a $3 stop-lamp bulb that kills those things. That is why it is important to use MB OEM European-made replacement bulbs - not Chinese-made 1157's from Auto-zone.

mdhegh · #3 10-28-2009, 09:00 AM

I am having similar problem 92 300d I just got running. Cruise will engage but is erratic and kicks out with a very unpleasant letdown. I am thinking It has to do with the speed sensor, but am unfamiliar with diagnosing and repair of these units.

blankenship · #4 10-28-2009, 10:23 AM

no change in behavior between JY and stock. just plain DEAD.

anybody got a link to a good troubleshooting / diagnostic post?

sasquatchgeoff · #5 10-28-2009, 10:51 AM

fuse?
continuity between cruise-amp/jumper/actuator?

http://gdl-online.com/begin1.html#contents

sasquatchgeoff · #6 10-28-2009, 11:12 AM

Quote:

Originally Posted by mdhegh

I am having similar problem 92 300d I just got running. Cruise will engage but is erratic and kicks out with a very unpleasant letdown. I am thinking It has to do with the speed sensor, but am unfamiliar with diagnosing and repair of these units.

Go to junkyard get new good used sensor - remove/replace via Instrument cluster -