Cruise Control on '97 Lesabre

[happydog500]

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.

[pcmos]

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.

[happydog500]

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.

[pcmos]

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.

[pcmos]

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

[pcmos]

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.

[happydog500]

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

Chris.

[pcmos]

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.

[happydog500]

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.

[kelshm]

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!