Help needed diagnosing/repairing cruise control
Thread Starter
Pro
Joined: Dec 2006
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From: Kennewick Washington
Help needed diagnosing/repairing cruise control
I have a 1996 LT-4 Roadster with 30,000 miles on it. This morning the cruise control worked poorly, did not hold speed accurately. On the way home from work it failed all together. I checked the fuse, hoses, and actuator cable and they all look good. Where do I go from here in diagnoising and repairing this item? The clutch and brake pedal switches also seem normal.
FWIW this happened about a year ago and 'fixed' itself.
Thanks for the help guys!
FWIW this happened about a year ago and 'fixed' itself.
Thanks for the help guys!
Le Mans Master
Joined: Jan 2006
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From: Woodstock Georgia
I spent a ton of time diagnosing mine using the FSM and followed all of the procedures only to find out the brake switch was faulty. What I did learn is the module is an absolute PITA to get to, plus they rarely go bad. Brake switch is easy, relatively cheap and likely the cause.
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From: Rolla Missouri
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In this case, I don't think so Mike.
My LT4 does this from time to time also. You can be driving down the interstate with cruise on, and it just shuts off (exactly like it does if you tap the brake or clutch).
It only does this once in awhile. When it happens, just wait a second and push the set button and it works again.
If it was vacuum, wouldn't it act up a little differently?
I can go for months without any issues at all. That's probably the reason I haven't even looked in too this issue. It happens so rarely, I haven't looked in too it.
My LT4 does this from time to time also. You can be driving down the interstate with cruise on, and it just shuts off (exactly like it does if you tap the brake or clutch).
It only does this once in awhile. When it happens, just wait a second and push the set button and it works again.
If it was vacuum, wouldn't it act up a little differently?
I can go for months without any issues at all. That's probably the reason I haven't even looked in too this issue. It happens so rarely, I haven't looked in too it.
Le Mans Master
Joined: Jul 2007
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From: Tampa Florida
Le Mans Master
Joined: Jan 2006
Posts: 5,620
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From: Orlando FL
I spent a ton of time diagnosing mine using the FSM and followed all of the procedures only to find out the brake switch was faulty. What I did learn is the module is an absolute PITA to get to, plus they rarely go bad. Brake switch is easy, relatively cheap and likely the cause.
I spent MANY hours of time over a couple of weeks of work and testing. I went further than most might have gone. It turned out to be that switch assembly.
Check my post a decide for yourself.
http://forums.corvetteforum.com/c4-t...-for-94-a.html
Thread Starter
Pro
Joined: Dec 2006
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From: Kennewick Washington
OK, couple of questions.
I appreciate the link to the other thread.
Could it still be the switch and my brake lights function normally?
I looked under the dash at the brake pedal, and holy cow is it tight in there! Where's the switche(s)? Do you need to train a chimp to get under there or can a 6'1" 45 year old get to it?
I don't see a tear in the vacuum actuator. If I need to test it, how do I do so? I have a handheld vacuum pump/tester.
The connections to the actuator are clean and seem sound.
Nothing works in the cruise system, neither the set nor accelerate position.
I really rely on the cruise to help keep me from getting too many tickets!
I appreciate the link to the other thread.
Could it still be the switch and my brake lights function normally?
I looked under the dash at the brake pedal, and holy cow is it tight in there! Where's the switche(s)? Do you need to train a chimp to get under there or can a 6'1" 45 year old get to it?
I don't see a tear in the vacuum actuator. If I need to test it, how do I do so? I have a handheld vacuum pump/tester.
The connections to the actuator are clean and seem sound.
Nothing works in the cruise system, neither the set nor accelerate position.
I really rely on the cruise to help keep me from getting too many tickets!
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Thread Starter
Pro
Joined: Dec 2006
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From: Kennewick Washington
It looks like one switch body but two sets of contacts, one for the brake lights and one set for the cruise. Am I understanding this right? How do I teleport the switch out and onto my workbench?
Le Mans Master
Joined: Jan 2006
Posts: 5,620
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From: Orlando FL
The electrical switch assembly has 3 sets of contacts in it and all are independent circuits. One for brake lights, cruise and TCC lock up. I took all out and cleaned them up.
My vacuum hose had a coupling 6 inch back from the switch so it was easy for me. But I could not get the hose off the actual vacuum switch assembly by pulling it.
I am a lot smaller than you and have no problem laying under the dash getting my feet in the air. But I can see where a big guy might have a problem.
Last edited by pcolt94; Nov 19, 2009 at 10:15 PM.
Le Mans Master
Joined: Jan 2006
Posts: 5,620
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From: Orlando FL
No, there is no easy way to check the switch. The wires run back to the cruise module on the passenger side. Getting to it is a huge effort as you can see the picture in my post. I measured my switch remotely several times and it checked good. I could do it because I had the module out a the time. An then it finally checked bad and I caught it.
The switch seems to go bad on a slight marginal basis. Does not always show bad till a current runs thru it. That is why all these cruise problem are intermittent come and go problems.
The switch seems to go bad on a slight marginal basis. Does not always show bad till a current runs thru it. That is why all these cruise problem are intermittent come and go problems.
Thread Starter
Pro
Joined: Dec 2006
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From: Kennewick Washington
Thanks for taking the time to help me out. I'll pay it forward to be sure. When I get back from my conference I'll dig into it.
I'm recovering from a motorcycle accident and my hands and knees are still busted up so it's a bit hard for me to get in there. Even if I can't do it in my current state I can at least tell the shop where to start and that would still save me time and money. Hopefully!
I'm recovering from a motorcycle accident and my hands and knees are still busted up so it's a bit hard for me to get in there. Even if I can't do it in my current state I can at least tell the shop where to start and that would still save me time and money. Hopefully!
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
