A search returns a handful of posts about our cruise controls, and more often that not is seems to be a computer refresh is needed. I am doubtful I can twist my old body around enough to get the cpu out. I was able to take a video with my phone while moving each pedal and I see the switch plungers moving in and out, so they are at least not physically stuck but that doesn't mean they actually work. My different question is on the connections to these two switches. Do they just pull off or are they captive? I wiggled a little with limited visual, they did didn't just pop off. I though I might be able to use my ohm meter to see if the switches are opening and closing without being a shape shifter, but I don't want to break them because they are captive and I can't see or feel the release.

I'll add on to this my symptom. It isn't intermittent for what that's worth. A month ago I engaged the cruise, it worked. I tapped the brake and it disengaged, it has never engaged since. The only other useful clue I have is that the column switch appears to work, I say this because the acceleration function works fine, and that is the same switch position as the engage position, telling me, I think, that the column switch is not the issue.

 

One factor I was previously unaware of was that the sunroof must be operational for the cruise control to operate.

Above 3-5 mph it signals through the can bus system to lock the motor. If the signal isn’t triggered, cc will not engage.

 

That's crazy! If it was April 1 I would assume this information was a joke! Or possibly a failed AI response! I have been very reluctant to open my sunroof for fear that if it did open it might not close since the last time I actually opened it was probably some time in the 90s. Any way to confirm this isn't the issue without actually opening the sunroof,? Or perhaps a better question to ask would be how would this "feature" be bypassed?

 

I went through almost the exact same thing on my 968, so before you pull the control unit, I’d take a look at the clutch and brake inputs (assuming your car isn’t a Tiptronic).
Per the factory wiring diagram and WSM, the clutch input is simply a ground-triggered logic signal. The cruise module has an internal pull-up resistor.
So:

• Switch closed → input sees ground → cruise allowed
• Switch open → input floats high → cruise disabled

If that input stays “open,” the module thinks the clutch is pressed all the time and won’t engage.

In my case (Tiptronic), there’s no clutch switch. The wiring diagram literally says:
“In case of automatic transmission bridge to ground instead of switch.”
Pin 7 had lost proper ground. Once I restored it, cruise worked immediately.

Since yours disengaged after a brake tap and never came back, I’d strongly suspect one of the interrupt inputs (brake or clutch) is now electrically open — even if the plunger moves fine. Mechanical movement doesn’t guarantee electrical contact.

Before pulling the module:

• Disconnect the cruise control connector.
• Check clutch continuity to ground (pedal released).
• Verify the brake and clutch switches per WSM procedure (attached PDF).

Very often it’s not the computer, it’s just a missing ground signal.

I’ve attached the relevant wiring diagram and WSM pages (PDF-File) for reference and testing.

Hope that helps before you turn yourself into a yoga instructor under the dash 😉



Checking Pin 4 and 7

 

I've owned two 968s and this has not been my experience (sunroof must be operational for the cruise control to operate). On my 1992, the cruise control worked perfectly and my sunroof never worked. It was never opened and I never attempted to open it because the seller noted there was an issue with it. The seller was upfront about everything and he suspected the classic gear failure in the roof. He also stated that he had not opened the sunroof in several years. It was an issue I always wanted to correct, but never did. On my 1993 the sunroof did not work when I purchased it and it was fixed. The cruise control worked before and after sunroof repairs on my 1993.

 

I'm preparing to leave for Amelia, so I don't have time to review the wiring diagram. But I can say that our cars are not OBD2 and do not have a body control module, which is the unit that might have the ability to shut down one system over an issue in another. Volvo had this issue with their models years ago. The alarm horn would fail and the BCM would then disable the sunroof, but only AFTER you had opened it!! Stupid...

Bosch did start can bus technology in the early 90's, but only in a handful of models (IIRC the first was Mercedes) and I never saw 968s on the list. I have also owned 968s with operating roofs, some with inoperative roofs and the cruise still works in my track car whose sunroof motor is removed. I know, you're asking "Why does a track car have cruise??" The PO drove it to and from the track and I've just never taken the time to remove it.

Cliff

 

Reflowing the solder connections on the CC brain board has worked for me. I don't think what you are describing suggests something other than a typical cruise brain issue.

 

Thanks for all the inputs so far. I have been sidelined for a bit but I will resume this when I can. Just FYI, 2 days ago I tapped the cruise and magically it once again engaged. It was a short enough trip that I didn't try on/off to see if it would engage a second time. So at best this is an intermittent problem, so easily can a connectivity problem yet to be identified.

 

My intermittent cruise problem was totally resolved with someone reflowing the computer's circuit board. Don't know if he does it any more but it was well worth the cash and effort.

 

Not ready for a celebration yet, but when my cruise worked the other day, I decided to see if could get it to engage again today. It did not at first. My first experiment was tapping the clutch pedal several times to see what happened. Nothing happened, cruise did not engage after doing that. I then tapped the brake pedal several times and after that cruise did engage and continue until I terminated it successfully with another brake tap. I engaged it a couple more times after that. I repeated the test on a second trip about an hour later and got the same results. Tapping clutch pedal had no effect, tapping the brake 2-3 times and then cruise engaged and remained engaged until I cancelled it. This is not a slam dunk, but it is at least a bank shot. It seems to clear the clutch switch/interface, and targets the brake switch/interface. While the physical switch is for sure at the brake pedal, the other end of the wire is, well at the other end. So it's possible the switch isn't really the problem, but it seems like it definitely could be, I'll repeat this experiment for a while and see if the results are consistent and at some point assuming this continues to repeat, I'll attempt cleaning the switch. I may be able to put a bunch of paper towels in the vicinity of the switch and spray some contact cleaner up into the switch as well as the connector contacts. I'd be more hopeful if gravity was on my side for getting the cleaner into the switch, but I'll at least start with the clean in place plan before trying to twist around and get up in there to remove the switch for cleaning, or replacement. Will post how the process goes for future reference....

 

Nice work. The cooled seat on the driver side is the same. Turn on p/s for 5 min, THEN turn on d/s and only then it works.

Yea for the small wins

 

Pardon my ignorance but, p/s and d/s? What are these? And, cooled seat on a 968?