I just bought my first Mercedes (96 c280 sport) and there seems to be a problem with the cruise control.

If I start the car and activate cruise soon after it seems to work fine most of the time.

If I drive the car for a longer period of time before trying to activate cruise it will not activate until I turn the engine off and restart it. I have also found that if I am using cruise and hit the brakes I cannot reactivate the cruise without turning the car off and restarting it.

If I cancel cruise using the column switch I can turn it back on again as long as I do so after only a short time.

Does anyone have any thoughts on this? Is there some sort of vacuum operated control that may have a leak? Any help would be appreciated.

Thanks in advance.

 

Disengaging with the lever works, but using the brake disables the system; sounds like the brake is not returning fully to the rest position. Drive the car, stop (using brakes), then get out and see if the brake lights are still illuminated. As long as they are on, the cruise control will not engage. Changing the brake light bulbs to LEDs may also create problems.

 

I tried checking the brakes they seem to disengage normally and the brake lights will go off. I'll have a look for the cruise brake safety switch perhaps it is the problem.

I'm still waiting for a repair manual to arrive, do you Know if there is an actual switch under the dash or is it something electronic in the ABS system?

Thansk for the reply!

 

I can't answer that. My MB's are all either ten years older or ten years newer than yours. My reply was generic in nature and derived from experience with the older models. In my older cars (mine are '83 300CD and '85 300SD), the cruise control disengage signal is grounded through the brake light bulbs; when the brake is applied, the power applied to the brake lights also sends a positive voltage to the CC to disengage.

My newer MB is an '06 E320 CDI. I guessing that it may use some different logic altogether. Everything is computer controlled, probably including the digital CC. The disengage signal may still be generated the same way with the brake lights, but who knows? Wiring diagrams are less meaningful with the computer controlling so many functions all around the car via the digital busses.

I'm sorry my suggestion did not work. Your thought about a sticky signal switch seems logically correct provided such a switch exists.

 

Thanks, again.

 

did you try changing the brake light switch?they do give problems on these.