Problem with cruise control
Thread Starter
Burning Brakes
Joined: Nov 2002
Posts: 807
Likes: 21
From: Los Altos CA
Problem with cruise control
The cruise control on my 2000 auto c5 stopped working and I have done quite a bit of diagnosis with little luck. I don't get any codes that I can tell. Most of the wiring goes to the TAC (throttle control module) and I was able to remove a connector and check the function of the switches on the turn signal stalk. Everything was fine. Then I checked the brake switch (which goes to the same connector). It showed 12V when the pedal was depressed and 0 when not applied. This is the opposite of what the switch should do in the cruise control section of the manual. It says is should be open when the brake is depressed and close with the brakes released. However, this same switch (according to the schematics in the manual) operate the third brake light and hence should be closed when the pedal is depressed, which is what is actually happening. That is, the manual is inconsistent.
Nothing else in the car appears to be malfunctioning. Any suggestions.
Nothing else in the car appears to be malfunctioning. Any suggestions.
Pro
Joined: Jun 2003
Posts: 702
Likes: 0
From: Castle Rock Co
Originally Posted by white90conv
The cruise control on my 2000 auto c5 stopped working and I have done quite a bit of diagnosis with little luck. I don't get any codes that I can tell. Most of the wiring goes to the TAC (throttle control module) and I was able to remove a connector and check the function of the switches on the turn signal stalk. Everything was fine. Then I checked the brake switch (which goes to the same connector). It showed 12V when the pedal was depressed and 0 when not applied. This is the opposite of what the switch should do in the cruise control section of the manual. It says is should be open when the brake is depressed and close with the brakes released. However, this same switch (according to the schematics in the manual) operate the third brake light and hence should be closed when the pedal is depressed, which is what is actually happening. That is, the manual is inconsistent.
Nothing else in the car appears to be malfunctioning. Any suggestions.
Nothing else in the car appears to be malfunctioning. Any suggestions.
Melting Slicks
Joined: Jun 2005
Posts: 3,088
Likes: 61
From: NY- 2013 Corvette Challenge Champion-2013 Index Combo Champion 2015 CC/MM Champion
St. Jude Donor '07
Try lifting the back of the brake pedal with the back of your foot while your driving and set the cruise at the same time,The switch might need to be adj.
Drifting
Joined: Oct 2003
Posts: 1,540
Likes: 0
From: bloomfield nj
Originally Posted by white90conv
The cruise control on my 2000 auto c5 stopped working and I have done quite a bit of diagnosis with little luck. I don't get any codes that I can tell. Most of the wiring goes to the TAC (throttle control module) and I was able to remove a connector and check the function of the switches on the turn signal stalk. Everything was fine. Then I checked the brake switch (which goes to the same connector). It showed 12V when the pedal was depressed and 0 when not applied. This is the opposite of what the switch should do in the cruise control section of the manual. It says is should be open when the brake is depressed and close with the brakes released. However, this same switch (according to the schematics in the manual) operate the third brake light and hence should be closed when the pedal is depressed, which is what is actually happening. That is, the manual is inconsistent.
Nothing else in the car appears to be malfunctioning. Any suggestions.
Nothing else in the car appears to be malfunctioning. Any suggestions.
are you sure you are looking at the right part of the switch? you should
be looking at the part of the switch that has the purple and pink wires[i think the colors are right].it should have 12 volts with the pedal not being pressed and 0 with it depressed.the same switch also disengages the converter clutch.go out and drive it,get up to like 45-50 mph and tap the brake pedal,the rpm's should jump up about 200 rpm's,if it does it means the switch is working[because it unlocked the clutch],but if it didn't the car should stall at a idle.
FWIW,you should have some type of fault stored in the pcm.if you don't you may have a bad stalk switch[won't turn the system on],if you have access to a tech II or good scanner you can see the switch functions.also if you've changed rear brake bulbs,make sure they are all the same[there are gold bases and silver bases].even though the brake lamps work,if the resistance values are different the controllers will think the bulbs are out and keep cruise disengaged.
Thread Starter
Burning Brakes
Joined: Nov 2002
Posts: 807
Likes: 21
From: Los Altos CA
Thanks, Dpd, for your ideas. I checked the brake and the TCC is locked when the brake is released and the TCC disengages when the brake is tapped. The only codes are in the RF? module that controls the fobs and door locks (several U codes that I believe come from door lock problems). The stalk switches are all ok because I checked them by disconnecting the connector at the TAC module. All three switches work as expected. It's beginning to look like it is either the TAC module or the PCM. I will probably have to take it to someone with a Tech 2 unless someone has another idea.
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Thread Starter
Burning Brakes
Joined: Nov 2002
Posts: 807
Likes: 21
From: Los Altos CA
I found the problem with my cruise control - it was a high resistance in the off-on switch on the stalk. The voltage at the TAC module from the switch were ok but when there was a load on the circuit, the voltage dropped to zero. I simply jumpered the switch at the connector under the dash so the cruise control is now always on. Replacing the stalk is a major job which can wait till later.
Thanks for the help anyway.
Thanks for the help anyway.
Instructor
Joined: Dec 2005
Posts: 102
Likes: 0
From: Carnegie PA
stalk
Not sure if they changed things from 86 to 90 but stalk replacement is pretty easy on the 86. No steering wheel removal required!
That's what the cruise problem was on mine. Very dirty switch internals.
The hardest part of the job is removing the under dash insulation panel.
pm me for details if interested.
That's what the cruise problem was on mine. Very dirty switch internals.
The hardest part of the job is removing the under dash insulation panel.
pm me for details if interested.
Burning Brakes
Joined: Mar 2005
Posts: 1,227
Likes: 15
St. Jude Donor '06
Originally Posted by white90conv
I found the problem with my cruise control - it was a high resistance in the off-on switch on the stalk. The voltage at the TAC module from the switch were ok but when there was a load on the circuit, the voltage dropped to zero. I simply jumpered the switch at the connector under the dash so the cruise control is now always on. Replacing the stalk is a major job which can wait till later.
Thanks for the help anyway.
Thanks for the help anyway.
