Cruise Control on '97 Lesabre

I have a '97 Lesabre and the cruise control will work perfectly sometimes but most often will not engage at all. The Cruise light on the dash doesn't come on unless it is actually working. Generally it will stay engaged until you shut it off but once it quit without shutting it off. Any ideas?

Sorry to see hear problems with Cruse.

I had cruise control problems on my 97. Not sure why, but I had most all questions answered, except Cruse Control. I searched this and other forums, but they to, when a cruse control question was asked, no answers.

Don't know why that is, just seems to be a thing I noticed on the forums. If you do get it fixed, post back to let others know what it was. It's been a couple years since I got to use cruse.
Chris.

my 92 did the same thing never figured it out but it work know thing to look for the brake switch ,bad light bulb next time that happens try pulling up on brake peddle that might rule out the switch or check it with a meter good luck

I know that lifting up on the brake pedal doesn't change anything. I have read somewhere, and I forget now where, that the on/off switch often goes bad in these cars. It is also the turn signal lever. I'm thinking you can change it in this car without removing the steering wheel and air bags. I suppose if that's the problem it will have to wait as I just got laid off.

That is a good thing to check. If the middle tail light (the one in the back window) goes out, the cruse control quits working.

When mine quit, I checked, and the light was out. I was so happy!! It was an easy fix. Until I changed it, and it still didn't work.

It could be the problem for you, check to see if it's working.
Chris.

You may have a problem with the cruise/shift interlock brake switch located under the driver side dash and above the brake pedal. I agree, the bulb in the rear/center high mounted brake light should have no effect on the cruise shutting off, it is controlled by the adaptive light monitor control module. If you do have a problem with the rear/high mounted brake light, this again could point back to the brake switch. If the brake switch is not functioning properly, you will not have power to the adaptive light module that controls the rear/high brake light. The white wire (W) from the brake switch feeds the module for power to the rear/high brake light. BTW, you have a PM with a schematic. Good Luck!

I know that lifting up on the brake pedal doesn't change anything. I remember looking at the break pedal now. I agree, it doesn't change anything. On mine, the 'Cruse" light comes on.
Chris.

Since the brake switch was so cheap, I went ahead and replaced it. It didn't change anything.

Answers that don't work are an improvement over not getting any replies at all.

With other stuff, there's a few basic things it could be. Ways to check what's wrong. Must be something with Cruse Control that makes it different then even the most complicated things on a car.

I looked all over the internet. I still don't know how to check what's wrong with Cruse. It's been two years.

Chris.

Okay, just to fill everyone in, I've been chatting with happydog500 via private message.

I have some free time right now because I'm currently biding my time while waiting for this dumb economy to yield some employment for me.

In the mean time I'd like to finally put this cruise control issue to rest. The cruise control system is really simple. Out of all of the computer controlled systems in this car, the cruise control should be one of the easiest to diagnose.

I'm working from the shop manual for the 1999 LeSabre, which should be identical to the 1997 and 1998 models. Cruise control is also the same for both the Custom and Limited models 97-99. Hopefully I can figure out how to post some diagrams on here. I doubt GM will care if I copy their shop manual, they're busy doing other things right now.

First and foremost we need to look at the primary component of the cruise control system.

The cruise control module is the "controller" or "computer" that handles all of the cruise control functions. The module itself consists of an electronic controller coupled with a small electronic stepper motor (like a hobby motor from an RC car kit). The electronic half of the module moves the small motor which literally pulls on the throttle cable to maintain the vehicle speed.

The cruise control module is located on the firewall next to the brake master cylinder and brake power booster assembly. It looks like a small black box bolted to the firewall with throttle cables going to the throttle.

Fortunately the cruise control module is highly independent compared to other vehicle modules. The cruise module is NOT connected to the class 2 vehicle network. It's a form of an input / output controller design.

Inputs:
Cruise ON Switch (located on the turn signal lever)
Cruise Set/Coast Switch (located on the turn signal lever)
Cruise Resume/Accel Switch (located on the turn signal lever)
Brake Pedal Switch - TCC (located above brake pedal)
Stoplamp Feed Circuit (part of the brake pedal switch)
Cruise Disengage Signal (comes from engine computer in case you go too fast or too slow)
Vehicle Speed Signal (comes from engine computer)

Outputs:
Throttle Angle (actuated by stepper motor as part of the cruise module)
Cruise Indicator Lamp (Located on the instrument cluster)

For each of the inputs the module expects a particular value. If the cruise module decides that any of the inputs are false or faulty, it switches into a "standby" mode. Based on my research, I believe that in standby mode the controller will illuminate the cruise indicator light, but doesn't actually move the throttle.

What we need to do is to figure out why the cruise module is failing to actuate the cruise by systematically checking all of those inputs listed above. If all of the input sources check out good, then the problem is most likely the cruise module itself.

Before checking out the inputs to the cruise control module we need to check one really easy possibility. The cruise control module and most computer modules in the car depend on a really good ground to the vehicle chassis. Control modules in general operate by switching and manipulating grounds.

There is a ground post called G104 which directly grounds the cruise control module. The ground post is located under the air cleaner box on the vehicle frame rail. There are actually two ground posts near one another on the frame rail under the air cleaner box. Both grounds need to be absolutely clean metal to metal contacts with the vehicle frame.

Before trying to diagnose anything else, your first step should be to locate those two ground posts under the air cleaner box. Remove the nut, pull off the ground terminal and scrub everything with a wire brush until you have bare metal with no corrosion, rust or paint, then put the terminal back on and tighten the nuts. It's tough to tell which of those two grounds are G104, so do both of them to be sure, it can't hurt.

I've uploaded an image from the shop manual that shows G104. The image is pretty crummy. I don't have this car so I can't go put my hand on the ground post. It should be easy to spot, it's definately on the frame rail under the hood either under or near the air cleaner box. If you can't find the ground posts I'll go look on my car and see if the 04 has the same ground locations by chance.

In general when you have any problem with an electronic module on the car, its a good idea to track down all the ground locations required by the module and clean them. Make sure they're making good contact with the chassis. Grounding problems can cause all sorts of whacky behavior from the computer modules. I've learned my lessons about grounds the hard way.

http://www.hireajklages.com/car/car1.gif

Here is a graphic image from the shop manual showing the location of the cruise control module itself. The cruise control module is labeled as item #2 in the image.

http://www.hireajklages.com/car/car2.gif

OK, thanks for the information. I will try and do the ground check/clean in the morning.
I did a quick look but didn't' see the ground post. It was just a quick look. I didn't take the air box off at that time.

Chris.

Okay sounds good. Clean those ground connections even if they don't look bad or loose or corroded, just to be absolutely sure. Wire brush everything so you have good clean metal to metal contact when you tighten the nut back down. Then it's easy to rule that out as a simple solution.

Do you own or have access to a good digital multimeter with a resistance mode? I'm going to try to think of a way to test those other input sources at the cruise module connector itself with nothing but a digital multimeter. Hopefully I can help you diagnose the problem without the use of a scantool system.

Checked the ground. No ground anywhere on what I thought is the frame rail.

Did see two bolts behind the computer. Still doesn't work.

I do believe I have access to digital multimeter with a resistance mode.

Some friends and I will be travailing on a long road trip (1,800+ miles RT) in a little less then two weeks, so lets get going on this. I'd hate to do this trip without a cruse.

Thank you,
Chris.

First of all you have to understand you are trying to step through a complicated diagnostic with virtually none of the neccessary diagnostic tools. Your chances of success on the first shot here are extremely limited because of your lack of an appropriate scantool device for this car. To make matters worse you are diving into the deep end of DIY repairs. This isn't like replacing an alternator. Your car integrates approximately a dozen different electronic systems in a complicated interconnected network. Sorting through all of that without having any way to communicate with that system is virtually impossible. There is a reason why these sorts of complex electronic problems aren't often tackled on the forums. It takes extreme care, caution and patience to methodically work backwards from the simplest possibilities until you have identified the suspect part.

I can't possibly reccomend taking one more step until you find those grounds. There is no way in the world that you should go out and spend hundreds of dollars replacing various components at random without ruling out something so simple and free. What I can gauruntee is that the grounds absolutely exist in exactly the place I described. Unfortunately the graphic is crummy, but you've got to try and muster the patience to continue searching under the hood. The shop manual states very clearly that G104 is located "Left front of the engine compartment, near the air cleaner housing". That's a direct quote from the shop manual. I wish I had access to a 97-99 LeSabre so I could go out and photograph the configuration but I don't. If you want to go out and remove the air box and post pictures I might be able to point out the grounds. They are absolutely in that general vicinity and they need to be located, cleaned and re-attached before proceeding any further.

In the mean time I will take a second look at trying to think of a way of using a multimeter to do the job that is normally reserved for a 2500+ dealer scantool. Just please understand you are really pushing the bounds of what can be done DIY style without professional equipment. I'm all about DIY but I've invested thousands of dollars in professional level diagnostic equipment, because cars are my hobby. Some things are beyond proper diagnosis if you don't have those tools.

As of right now you basically have four primary options:

1. Take your car to a dealer and have them tell you what is wrong by using the Tech 2 and their extensive experience and pay them a diagnostic fee.
2. Purchase the AutoEnginuity scantool package with enhanced GM support to use on a laptop PC. Use the AutoEnginuity system to quickly scan for trouble codes and take the place of the dealer Tech 2.
3. Start replacing expensive components at random by making limited educated guesses until you finally happen to replace the bad part.
4. Follow along with me step for step starting with the grounding system to work your way up to a likely diagnosis. (still not a gauruntee)

Frankly if I were in your boat right now with no proper diagnostic equipment, no documentation, and limited experience with the integrated vehicle control system I would be at the dealer. If you can't afford the dealer diagnostic fee then I can try my best to point out cheap alternative methods. As a final note though, on gut instinct alone I would suspect either the brake pedal switch or the cruise module itself. Both of which will set you back a fair chunk of change. They also both require care and caution to service as they are systemically critical to the operation of the vehicle. The cruise module is linked with the main throttle mechanism. The brake pedal switch plays a critical role in the operation of the transmission and torque converter clutch.

What happened?

First you tell me, "In the mean time I'd like to finally put this cruise control issue to rest. The cruise control system is really simple. Out of all of the computer controlled systems in this car, the cruise control should be one of the easiest to diagnose."

The next thing you tell me is, "First of all you have to understand you are trying to step through a complicated diagnostic...To make matters worse you are diving into the deep end of DIY repairs. This isn't like replacing an alternator.... There is a reason why these sorts of complex electronic problems aren't often tackled on the forums."

I will take a picture of the ground wires I see on the inside of the fender and post back.
Chris.

Both quotes are entirely true at the same time. This IS one of the easiest systems to diagnose. If you were trying to diagnose virtually any other electronic system in the car without a diagnostic scantool and shop manuals, you wouldn't stand a chance.

You've got some possibility of working through this but I can't help if you can't follow through with the first step. Finding the grounds and cleaning them is extremely important because we don't have a scantool to verify the other input functions. In other words if you had a scantool you could plug it in and watch the switches activating on a single screen and without even popping the hood you could stand a good chance of immediately identifying the problem. The only way you will be able to verify the switch functions without a scantool will be to work from the module plug itself and carefully probe specific pins with a multimeter. Using that method you won't be able to see all of the switch inputs simultaneously like you would with a scantool. I'm hoping that method will give you the ability to catch one of the switches acting up. Unfortunatley though, the use of the multimeter isn't going to help if you don't have a well established ground at the connector.

A faulty ground is also really simple to fix. I've had a lot of experience with poor grounds on these cars causing all sorts of weird problems that's why I always rule that out first. In the 2000 model year they switched to a more reliable grounding scheme with plastic shielded metripack connectors.

Okay, let me post some more information from the shop manual at this point.

I have two images and a PDF file for you to take a look at. The graphics are the two circuit diagrams for the entire cruise control system. They simply divide the schematics into two graphics to keep things from getting too cluttered. Please keep in mind that the main object in both schematic diagrams is the cruise control module itself. You can see where the ground is called out in the schematic diagrams. I'm sorry for the huge size of the images but if I reduce them anymore the text becomes impossible to read.

The PDF file is a copy print fom the shop manual which shows the pin diagram for the only connector on the cruise control module. I'm posting the PDF link right here because I don't want it to get lost below the relatively large schematic images.

http://www.hireajklages.com/car/car1.pdf - Cruise Control Module Connector Pin Diagram


http://www.hireajklages.com/car/car3.gif

http://www.hireajklages.com/car/car4.gif

Here is some more useful information for you to work with. This is all of the information listed under the "description and operation" section of the factory service manual. Each system documented in the service manual usually includes a "description and operation" section which simply details the operation of the subject system in paragraph form.

There are a total of three PDF files here which are three seperate documents under the "description and operation" sub section.

http://www.hireajklages.com/car/car3.pdf - Cruise Control System Description

http://www.hireajklages.com/car/car4.pdf - Cruise Control System Operation

http://www.hireajklages.com/car/car5.pdf - Cruise Control Circuit Description

Unfortunately most of the diagnostic procedures listed in the factory service manual integrate the use of the Tech 2 into the procedures. After you inspect, clean and re-attach the ground connections I'll try to help you get through the diagnostic procedures without using the factory scantool. That's where you will need to improvise a bit.

OK, thank you very much. I will get to the grounds and post back.
Could I take off the module and test it?

Chris.

Unfortunately I can't think of a real good way to actually "test" the cruise module itself, but the goal is to get at the connector and test everything else first. In other words you should be able to rule out every other possibility by pulling the connector off of the module and performing specific tests on each pin. Since we know what each pin's function is from the documentation.

If you look at the cruise module connector diagram which I posted in a PDF file there you'll see that there aren't a whole lot of pin connections to test. The pin diagram gives you a nice picture of the connector face and then a chart showing what each pin's function is.

Since you have a digital multimeter then the ideal way to test the ground is to pull that connector from the cruise module. Start by checking resistance between the connector ground pin and a clean metal chassis part or battery negative terminal. Then track down G104 on the chassis, remove it, clean it, replace it and do the same resistance check at the connector again. Compare the resistance readings before and after cleaning the ground. Obviously you want the resistance between the ground pin in the connector and the chassis to be virtually zero. If your multimeter has a continuity setting you should actually see full continuity between connector ground and the vehicle chassis or battery negative terminal.

By the way, I'm assuming you have already looked at the throttle linkages to make sure the cable isn't broken or detached from the cruise module in an obvious way. If you haven't checked those throttle cables, give them a once over, thats another simple explaination. Remember the cruise module works by physically tugging on the throttle linkage, if that cable is loose, disconnected, or broken, then the cruise will behave in a manner consistent with your symptoms.

After you verify the ground connection the next step will be to use the documentation i posted to check all of the inputs at the pins on the connector. For example if you read the document "Cruise Control System Circuit Description", it describes what happens when each component is activated. You should be able to use your multimeter at the connector under the hood while someone else activates the brake, and cruise control switches to verify their behavior. If all the inputs seem to be functioning properly but you still have no cruise, then it's pretty clear that the problem has to lie in the module itself. But the big thing is to use the multimeter to rule out a fault with the brake pedal switch assembly and the steering column mounted control switches. The goal is to go through a process of elimination until the only thing left is the module itself. Then you can feel pretty confident spending the money to replace the cruise module.

Got my Cruse Control working.

I went to the library and looked at a book.

The Cruse is a very simple system that needs no real special tools to check it.

The ground is grounded to the fender. If I take a test light and touch it to the fender, it's grounded. I figured the wire is bolted to the fender, it's grounded.

As mentioned, if you take the module plug off, you can put the light on the Gray Wire. Push the Cruse to on. If the light comes on, the multifunction lever works.

Same thing with the Purple Wire. Should be on. Push the brake. If the light goes off, the brake switch is working.

If everything checks out, it's the module.

I did not do the tests. What I figured was, since "Cruse" light came on when I pushed the lever, it works. When I push the brake, the "cruse" goes out, so the brake switch is working.

I went to a nice wrecking yard that has the cheapest prices I know. The first car I came to (97 Century) had the same Cruse Module. I got it for $8.50. Put it on in the parking lot. On the way home, I have Curse.

Chris.

I'm saving all of this information for future reference but my cruise just decided to start working again. I didn't do anything to it, it just started working. It now works every time.

Cars....lol.....gotta love 'em!