Intermittent Cruise Control

I have a 1999 Riv with an annoying habit of the cruise control shutting off at random times. When ti shuts off, it won't resume but about half the time I can set the speed again. The other half of the time I have to shut it off for several miles and then retry to set it. The random cut outs are increasing in frequency. I don't know if it is a vacuum problem or maybe a servo over heating or what but anyone with some insights would be appreciated.

Thanks!

Dagwood
The owner of many dead and gone car lines:
1967 Oldsmobile Cutlass 442 Convertible
1973 SAAB Sonett III
1998 Plymouth Grand Voyager
...and some on hiatus:
1999 Buick Riviera

First thing to check is the brake light switch. Stepping on the brake will cancel any cruise control and the brake light switch is different for any cruise control equipped car.

Thanks. I checked that first and it isn't that. When the cruise control is working and I hit the brake, the cruise shuts of smoothly and will resume every time. But when the cruise cuts off on it own, the car will "shudder" like it is trying to maintain itself with a rapid set of pulses but fails.

Dagwood(TSRW) wrote:

Thanks. I checked that first and it isn't that. When the cruise control is working and I hit the brake, the cruise shuts of smoothly and will resume every time. But when the cruise cuts off on it own, the car will "shudder" like it is trying to maintain itself with a rapid set of pulses but fails.

In that case, I suggest you get an FSM and follow the trouble chart for the cruise control. Figuring out a problem without an FSM will be all but impossible unless you get lucky and find something obvious.

Awesome Buick technician training video reminds me of the "VD movies" from high school health classes:

https://www.youtube.com/watch?v=Q5SEy9GwQIw

I'm not sure this will help but on my '95 I had kind of the same problem, the cruise would just drop off and stop working, to fix it I just had to unplug and clean the connector at the servo, and plug it back in. It has acted up for me a few times over the years I have had it and that corrected my problem every time?

May or may not be your problem but it worked for me.

You mention a shuddering - I realize you say the brake switch disconnects the cruise control, but also realize the brake light switch will disengage the torque converter clutch. If the switch is adjusted too close and 'flickering' it could cause some weirdness with the TC at the same time as disconnecting the cruise.

I can't recall if this switch is a two-part switch, one for the lights and one for the computer (would do TCC and Cruise), or if it's just one wire going through the switch, but it's worth double checking to make sure that's not the issue.

This morning it was nice and "cold" (54F) here in south Florida. No trouble with the cruise. It may just have been luck but it makes me think...

As soon as I get a clear day without rain I will tear into this with my OBD2 reader/computer interface and my Fluke multimeter. I do think it is likely a connector or servo issue... I will let you know as soon as I get into it.

Any luck on figuring out this issue? I'm having the same problem, interestingly also in Florida, and it started the day I moved here. It's driving me a little crazy on my 60 mile commute between Cocoa Beach and Edgewater.

I believe the servo motor is getting hot and needs to cool off until it can reset the thermal overload. The only way to fix is to replace the cruise control box which runs about $425. The servomotor could be replaced but I have not been able to identify the manufacturer or part number.

Aha, thanks!  I had a suspicion that it was acting something was "overheating."  Wonder if I could get my hands on a used one somewhere.

Would this happen to be one of the boxes along the firewall in the engine compartment? Like the one with the barcode that says V6? Have never had to deal with a faulty cruise control system before!

Dagwood(TSRW) wrote:

I believe the servo motor is getting hot and needs to cool off  until it can reset the thermal overload. The only way to fix is to replace the cruise control box which runs about $425.  The servomotor could be replaced but I have not been able to identify the manufacturer or part number.

Your current servo should be numbered Delco/GM 25344189 {or GM 25140567}; if I am not mistaken GM used them in pretty much every Buick/Olds/Pontiac/Chevy midsize and up between 1995-1999... and so they ought to be available pretty reasonable from a recycler or a pick-n-pull. I doubt you'll need a new one to get a very good one.

Albertj

Dagwood(TSRW) wrote:

I believe the servo motor is getting hot and needs to cool off  until it can reset the thermal overload. The only way to fix is to replace the cruise control box which runs about $425.  The servomotor could be replaced but I have not been able to identify the manufacturer or part number.

Your current servo should be numbered Delco/GM 25344189 {or GM 25140567}; if I am not mistaken GM used them in pretty much every Buick/Olds/Pontiac/Chevy midsize and up between 1995-1999... and so they ought to be available pretty reasonable from a recycler or a pick-n-pull. I doubt you'll need a new one to get a very good one.

Albertj

After a few years of sometime on, sometimes off cruise control, I still haven't found the culprit. To date, I have disassembled, cleaned, and reassembled the cruise control module, replaced the brake switch, replaced the steering column uni-stalk switch, and cleaned every contact in the system. I have yet to take the big leap and replace the module as $425 is a bitter pill on a $3000 car. One thing is for sure, that module gets damn hot under the hood; even when not in use. I suspect there is a component on the circuit board that senses temperature of the unit and turns it off when a limit is reached. Most microcontrollers have an internal temperature sensor for power cutback/self preservation. If the bias resistor for that reference circuit drifts, the temperature trip point will drift as well. I am going to a scrap yard and see if I cant find a donor box and see if that will fix this.

Problem solved! I went to a very well organized scrap yard outside of Atlanta, GA where they gave me a print out of all the GM part numbers and the cars in which they can be found (make, model, and years) that would cross over to the Buick cruise control module including where on the car the part could be found and where in their lot the car with the module could be found. I pulled the newest cleanest module I could find in that lot (out of a 2006 Impala with 35K miles on the odo). They charged me less than $25 but no warranty so it was a $25 risk if it didn't work. I will accept a $25 risk when a reconditioned unit is over $400 with a 90 day warranty. So, I took it home, cleaned the connector contacts with electrical cleaner/lubricant, swapped in my throttle linkage cable, and installed it in its bracket on the firewall. Its been happy there ever since. It turns on and stays on until I shut it off or hit the brakes; just as it should. This unit doesn't get hot like the previous one so I am guessing the original unit was indeed over heating and tripping off line.

Dagwood(TSRW) wrote:

Problem solved! I went to a very well organized scrap yard outside of Atlanta, GA where they gave me a print out of all the GM part numbers and the cars in which they can be found (make, model, and years) that would cross over to the Buick cruise control module including where on the car the part could be found and where in their lot the car with the module could be found. I pulled the newest cleanest module I could find in that lot (out of a 2006 Impala with 35K miles on the odo). They charged me less than $25 but no warranty so it was a $25 risk if it didn't work.  I will accept a $25 risk when a reconditioned unit is over $400 with a 90 day warranty. So, I took it home, cleaned the connector contacts with electrical cleaner/lubricant, swapped in my throttle linkage cable, and installed it in its bracket on the firewall. Its been happy there ever since. It turns on and stays on until I shut it off or hit the brakes; just as it should. This unit doesn't get hot like the previous one so I am guessing the original unit was indeed over heating and tripping off line.

Congrats.

I copied Dagwood's repair yesterday. I've been without cruise control for about 1.5 to 2yrs and never have had a power antenna. I bought replacement parts yesterday and got the cruise control working. Only thing I'm wondering about is the module I bought did not have the same part# as my original. It did match what AlberJ listed as a possible part#.Picture of Original and Replacement Modules
what do you think? The cruise control worked, but I'm not sure what the difference between the two parts are? I don't like where this module is mounted in the engine bay, right above an exhaust manifold and not sure how much air flow that area gets at road speed either.

https://photos.app.goo.gl/tDZ49cXfciFdQsaz6

Oh, original on left, replacement on right.

Thanks for posting this as I'm having the same issue.