Installing Cruise Control on 1996 Buick Century Wagon - not working, yet

Added the cruise control brain, the actuator, and the column switch, all parts from the salvage yard, but I haven’t been able to get it to work, so far.

Cruise indicator light does not illuminate on the dash when following the GM shop manual “Additional System Check” on page 8A-34-3. Everything meters out, following the troubleshooting guide, so it seems to be hooked up OK. Had a local shop check it - they said the voltage is present at the cruise control module, but they couldn’t go any further.

Am I missing a part? A fuse? Do I need to somehow tell the PCM there is now cruise on this vehicle?

Appreciate any help.

hamilton101
Corvallis, Oregon

There’s a lot you haven’t told us. Is this a replacement for the original cruise control? Or did the Buick initially lack factory cruise control? It might make a difference.

Yes, most likely the PCM needs to know about the new unit. I am not sure of the wiring needs in this model, but the controller needs input from the speed sensor and also from the brake switch. These functions are typically decided by the PCM which then reports the information to the CC brain. In fact, some cars do not have a CC brain at all. They let the PCM decide everything.

If your car did not originally come with factory CC, there is the possibility it may not have the right brake switch or PCM programming. For now, check your wiring to each mentioned device.

Thanks, SteveF, for your comment.

The car did not have cruise control on it. This is a new installation, as far as I know. All of the connectors were present - it was easy to plug in the components. I have also traced the wiring, using the Factory service manual flow chart. Everything checks out as far as the connections go. When I use jumpers to the actuator, it moves as it should.

Just wondered if there is a trick to it, like programming the PCU?

Thanks!

I can’t tell you anything about your PCM, like whether or not it already has the necessary programming. Of course, the true question is “how do you know it’s not working”? One would normally get out on the road to test. Cruise control won’t kick in until you reach a speed of about 35 mph. You’ve tried it?

Also, is your actuator vacuum controlled or does it have an electric motor?

Hi SteveF -

Road test was done - that’s how I know it doesn’t work. The second test indicated by the FSM supported the result. Actuator is an electric motor - that’s why I could use jumpers to check it.

The question I have is about the PCM - does it need to be programmed to know there is a cruise control system installed? Anyone know?

Thanks.

How about the safety lock-outs that prevent the cruise from engaging?? Like the brake pedal switch…Also, you are assuming the control module is getting a speed signal that might not be present unless a sender is factory installed…

Took it to the dealer.

First question I had was answered - the PCM recognizes the cruise module without having to do anything - no programming, or anything.

Turned out the rear center light has to function properly for the cruise to work. There was a faulty ground - on the Century Wagon, the connection to the rear light comes through two contacts at the edge of the window. The ground side was worn, giving intermittent connection. Bending the tab slightly took care of the problem.

Kudos to the tech! He says these cruise controls are built to withstand nuclear war - he has only had to work on 5 or 6 of them in his career, and he was an older guy. And he had never seen anything like this one where the rear door connector caused the whole thing to go gunny bags.

Thanks for the update. And it is useful to know that a dealership can often provide answers that stumps the usual mechanics. Well, off you go now. Happy motoring.

After the car got home I had a better look at the situation. The glass in the rear hatch of the station wagon can be lifted up separately from the hatch door. There are two electrical circuits in the glass that are fed through flat pad contacts on the glass that hit a couple of copper connections in the rubber trim around the opening in the hatch. The two circuits are the glass defroster and the cyclops rear brake light in the middle. The pads on the glass oxidized over time creating an open circuit to the brake light and the defroster. We knew the brake light didn’t work, but we never needed to use the rear glass defroster in so cal so didn’t know it was inoperative.

Turns out the cruise control checks to see if the brake lights are connected properly - an open circuit causes the PCM to shut off the cruise. What’s the logic of that? I have no idea, but if the bulb is burned out, or if there is an open circuit, as in this case, the cruise won’t work.

Turns out the tech had to call Detroit to get the solution: clean the pads on the glass with sand paper, and presto! The cruise control, the center brake light, and the rear defroster all work!

Maybe this hard-won knowledge will be of some help to someone. At any rate, to add a cruise control to a 1996 Buick century (and similar design GMs), all you have to do is swap in the correct lever on the steering wheel (they just pull out- and the wires have a connector near by), and install the actuator in the engine compartment. If you pull your own module and lever at the salvage yard you will see exactly how to install them in your own vehicle. If it doesn’t work, check your brake lights - the tech says these vintage GM cruise modules are designed to withstand a nuclear blast.