FAQ: Cruise Control Problems

My cruise has been a problem. Normally, I press the switch, nothing happens. Sometimes, I press set, the cruise light comes on, I let off the gas, cruise goes out. For a while, cruise worked wonderfully this last summer.
The fuse is fine, the switches are working, according to my scanner. This weekend, I checked my vacuum check valve, and it was not working. Nothing could come or go thru it. I replaced that, along with the hose from the tank and the source. Still nothing. I wonder if it is the PCM, but how do you even get to that thing. According to my shop manual, it is on the left side, under the master cylinder on the firewall. Does not look like a fun place. I have not checked my brake switches yet, as they are hard to get to, and I am not sure that is the problem, but I do plan on checking them. The problem seems to be more of a vacuum, or servo related.

did you try pulling up on the brake while engaging CC?

Yep, that did not work either.

Most likely it is not the PCM hardware. I've never taken mine out, but I thought it was located behind the glove box.

What year and model are we talking about?

95 Riv.

I had a problem with mine a few times and for whatever reason if it starts acting up I just unplug and plug the wires to the servo and it works fine. I know there have been corrosion issues on some of the underhood connectors, but that seems to fix my problem when it happens?

This is on my '95 also.

Hi all,

I'll be getting my Riviera back Monday or Tuesday (again) from various random repairs but while I'm waiting, I have a few questions about the cruise control.

The cruise in my '95 Riviera is not working correctly. You can press Set, and the cruise light comes on, but the cruise doesn't engage. i changed out the modulator with a known working one, still nothing. I noticed that when I undid the vacuum lines from the Riv, it did not do the tell-tale 'vacuum loss' hiss. The car the modulator came off of did. So, the modulator being good, am I looking at a vacuum problem? Maybe my check valve isn't working or I have a bad T fitting or line? Maybe the vacuum box canister thing on the firewall? Is there any other part of the cruise system that could cause the system to not work BUT the light to still come on? The only thing i haven't done is pull up on the brake pedal while trying to cruise but that's only because I haven't had the car for even 4 days since I bought it in May....

Any thoughts or advice on things to try is most welcome! Thanks!

-Andrew Z

this would require much poking around. my thoughts? dump it! who needs cruise anyway? i dont know? it puts me to sleep......

Z-type wrote:

Hi all,

I'll be getting my Riviera back Monday or Tuesday (again) from various random repairs but while I'm waiting, I have a few questions about the cruise control.

The cruise in my '95 Riviera is not working correctly. You can press Set, and the cruise light comes on, but the cruise doesn't engage. i changed out the modulator with a known working one, still nothing. I noticed that when I undid the vacuum lines from the Riv, it did not do the tell-tale 'vacuum loss' hiss. The car the modulator came off of did. So, the modulator being good, am I looking at a vacuum problem? Maybe my check valve isn't working or I have a bad T fitting or line? Maybe the vacuum box canister thing on the firewall? Is there any other part of the cruise system that could cause the system to not work BUT the light to still come on? The only thing i haven't done is pull up on the brake pedal while trying to cruise but that's only because I haven't had the car for even 4 days since I bought it in May....

Any thoughts or advice on things to try is most welcome! Thanks!

-Andrew Z

I'm pretty sure it was earlier in the 90's when GM finally switched their cruise control to an electric servo in place of the very unreliable vacuum actuated servos. I know for certain my '94 Regal had an electric servo-type cc. Was there a vacuum line on the cruise servo?

So my guess is it's probably not vacuum related. But again, the '95 tends to be a different animal than all the rest. Make sure the cable is hooked up properly on the throttle body. Doe the cable move freely?

It's also difficult to connect the cable on the cruise servo. If anyone was messing around with it I wouldn't be surprised if that end of the cable was not hooked up right and hidden. The connection to the cable on my '98 is inside the cc box.

I actually did not know they moved to electronic servos - thats interesting. However, mine is the exact same setup at my '88 and '89 Lesabres and Reatta. Two vacuum lines going to/from it. And I didn't check the cable for looseness, but it is hooked up - and agreed, it's a pain to connect sometimes haha.

I had a similar problem on my '88 Bonneville SSE once - the cruise wouldn't work and it turned out to be a vacuum line not hooked up at all. But like you said, I'm not sure if this is the same system now - it physically LOOKS like it though.

Oh and Robo - I once read somewhere "Cruise control? That's like surrendering!"

..

Well, I know it's been a while for this post, but I do have an update. I changed the coupler on my supercharger and noticed a vacuum line that I thought was ok, was actually broken! I replaced with it with the exact same line (I have a lot laying around or various sizes) and that fixed it. It was a rotted line at the check valve. There were also some other connections I replaced - clearly I had some dry rot issues and didn't know it.

Thanks for the update, Andrew. So your cruise control works now - great news!

Yep it actually working now is a HUGE relief...that's one of those things you don't realize how much you 'need' until it's gone!

Interesting fact: our cruise control unit, made by Delphi I believe, caught the attention of a friend of mine who's an engineer at Honda R&D. He noticed the same unit is used in many Honda engine, a very precise and reliable made-in-USA component!

Hm that is pretty interesting. I've also noticed a broad range of years and models those units were used in. Of course, I guess they were paired with anything with a 3800 since they've been around.

Interesting but not that surprising any more. Some Hondas use between 70-75% domestic made parts, and some Toyotas are even higher. Ironic that much of the perception that import vehicles are superior in quality comes from the fact that many aren't really imported anymore.

My '97 Riviera (with supercharger) has a failing cruise control. The light on the dash comes on briefly (with all the other diagnostic lights) when I start the car. When I depress the switch on the stalk, the cruise is activated only about 5% of the time. If I am able to engage it, it usually shuts off within 10 or 15 minutes without any warning, and then I can't get it to engage again. Pulling up on the brake pedal doesn't have any effect.

The other functions - wipers, washers, signals - on the turn signal lever all work as they should, so I'm guessing the problem isn't with the switch. Is it probably the cruise control module, or should I be looking elsewhere? Rock Auto has a new module (ACDelco part #25344189) for $443, but I'm hoping to find one off a parts car for a lot less. Is the module the same 1) regardless of whether the engine is supercharged?; 2) across the entire Riviera run from '95-99?; 3) across the entire GM product line (a module from a Cadillac or Buick Park Avenue is the same)? 4) used by other manufacturers, i.e. Honda or Ford?

Anything else I should check? Thanks much. I really need this for trips, especially to the upcoming Riviera Owner's Association Meet in Hershey in two months.

Neal Herman

seeing that you live in Washington and that the Govt. is on cruise control,why don't you celebrate diversity and get rid of your C.C?

Without a Factory Service Manual, there is no way to isolate a problem, and you will end up changing unnecessary parts in order to fix a problem. There are lots of other things that might be causing the problem. The wiring on these cars is substandard. Could be a wire. The only way to know is to follow the trouble chart in the FSM.

This was my solution to the problem, something to try anyway...

I have had the same kind of problems on my '95 from time to time, when it acts up I remove the connector at the module, clean the contacts as best I can and reinstall it, after doing that it works as advertised for a long time. I'm not sure if it a moisture thing or something else but it has taken care of my problem on more than one occasion.

sounds like the brake switch is loose or out of adjustment..

95 Riv Cruise control does not work. As far as I can tell the fuses are ok. This car only has 60K. What to do?

Does the cruise light come on when you turn on cruise control? Is this a naturally aspirated engine or the Series I Supercharged engine? If the latter...

Check all vacuum lines to and from the cruise servo located on top of the transmission/underneath the intake tube. Make sure electrical connector to the servo is plugged in all the way and no wires are frayed or disconnected. Check the vacuum reservoir box for cracks and things of that nature. When you unplug the vacuum line that runs underneath the vacuum reservoir box, normally it lets out all the vacuum with a pleasant 'hiss' noise. If not, something is leaky.

Most likely it's one of the vacuum lines cracked or disconnected. Pretty common problem with cars this age, even with that mileage.

also probe the brake pedal switch to make sure it's functioning properly.