How does cruise control work - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 02-13-2005, 04:28 AM   #1
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Default How does cruise control work

1994 L27 Olds

Problem: No response from cruise control switch at any speed.


What have I done:
- Replaced all engine bay vacuum hoses except U Bend
- Checked brake hose with air compressor
- Replaced multifunction swich now 3 times with 3 different 94 h bodies
- Checked fuse in lower right hand side panel above hush panel
- Visually inspected brake switch and servo unit
- Checked brake swich and it is aligned as nessessary
- Unplugged the car for a night to reset pcm

What do I do now?

I have a decent multimeter if that would allow me to test components if that would tell me anything, but no way of knowing color codes or contacts since I do NOT have a service manual.

And does my car, being a 94 have a cruise control module or does it run of the PCM?

What other components are used in the cruise control process?

Where is the speed sensor that chiltons talks about?
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Old 02-13-2005, 04:44 AM   #2
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The speed sensor is over by the diff. Top of the tranny, Held with a bolt or two. Can probably only see it through the passenger side wheelwell.

Make sure you get continuity across the switches, and check each switch to make sure it'* right. The PCM houses the cruise brainbox.

Scantool should help...
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Old 02-13-2005, 04:46 AM   #3
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Quote:
Originally Posted by Damemorder
The speed sensor is over by the diff. Top of the tranny, Held with a bolt or two. Can probably only see it through the passenger side wheelwell.

Make sure you get continuity across the switches, and check each switch to make sure it'* right. The PCM houses the cruise brainbox.

Scantool should help...

I thought it used that sensor but anyway the switches on the stick are good but how do i test continuity for the brake switch...anyone have color codes???


So this car does NOT have a cruise control module? Just integrated with the PCM?
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Old 02-13-2005, 08:50 AM   #4
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Yeah, I can watch like three or four swithes... the cruise set mph and the cruise servo % on my Actron...
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Old 02-13-2005, 10:56 AM   #5
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Don't have a '94 FSM. Check the RPO code. My '92 FSM for K34 cruise control shows that there are TWO brake switches related to the cruise. If yours is the same:

a brown wire feeds the TCC/antilock brake switch, (opens with pedal depressed) and a purple wire runs from it to the PCM with a splice (ppl) to the sequential fuel injection cell (looks like this interfaces with the throttle position sensor)

a gray wire runs from the on/off switch in the multi-function lever to the PCM with a splice (gry) to the cruise/shift interlock brake switch (opens with pedal depressed) from this switch a brown wire goes to the PCM

If the K34 RPO code matches and these color codes seem correct for your car, let me know and I can scan the two pages with the complete wiring diagram for you.
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Old 02-13-2005, 11:09 AM   #6
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Quote:
Originally Posted by bill buttermore
Check the RPO code.
If the K34 RPO code matches
Well, you can forget about checking the RPO code. Both my '92 and '95 have cruise but neither include a K34 on the RPO build sheet. The only match I could find was here in techinfo. Sorry 'bout that. :(
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Old 02-13-2005, 11:21 AM   #7
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Its most likely the cruise control sero motor assembly...located on the firewall on my 97...thats what usually goes out...not the stalk mounted switch...its a cheap setup...the throttle cable is moved by a thin strip of seat belt material on a roller...either that broke, the servo motor froze up, or the module died....
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Old 02-13-2005, 12:21 PM   #8
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On a '94, the cruise control is run by a vacuum modulator, near the throttle body. There are two hoses, and a wiring harness on this. One hose goes to the mainfold, the other goes to the brake light switch, where there is a valve that vents vacuum when you step on the brakes. In the modulator, there are two valves. One to vent the modulator, the other to let vacuum into the modulator. Sometimes these valves can stick, or not open or close properly. You might want to carefully disassemble the modulator, and make sure these valves are moving freely and able to seat properly. Also, the modulator body is made of plastic that can crack or break. You should also check the cable that connects the modulator to the throttle body, to make sure it moves freely, and is adjusted properly.
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Old 02-18-2005, 01:33 AM   #9
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I just wanted to thank everyone who contributed to this as I did find it to be a bad servo with the help of everyone who posted.

The case was not cracked So I am quite sure it had a fried circuit board.


So dont rule out anything when it comes to cruise.

Note: this was never throwing a code either with a bad servo.
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