GradyCheek

I own a 2008 Silverado and I have been having a very annoying problem with the cruise control. For the most part the cruise control works as intended, and when it is working, it stays on and does not cut off unexpectedly or change speeds. But sometimes when I start up the truck, it just will not turn on! I have tried different speeds, checked all the fuses, even tried at different engine temperatures; nothing seems to work, but usually I try again another time and it is working just fine again.

What could be causing such a strange issue? It is almost like the cruise control just doesn't turn on sometimes.

frogg

Check this out https://chevroletforum.com/forum/tah...m-36708/page2/ Might be your answer.

Chevrolet Customer Service

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This issue may be caused by the master cylinder pressure sensor, wiring/terminal or EBCM. These are just suggestions, they are not meant as a diagnosis.

I encourage you to consult with a certified technician. They should be able to offer additional information after inspecting the vehicle.

Please keep us posted.

Louis
GM Customer Service

MCC35

My cruise control would sometimes just not engage, then eventually it stopped engaging all together. The power light would come on but it just would not hold a speed. I saw one forum that said check the "brake light switch" under the dash right under the steering wheel. Well thank you whoever you are because sure enough you were right. For an $11.00 part on line it was an easy fix, except for the laying on my back under the brake pedal part.

eustis2010

Had the same problem, it was the brake lamp switch behind the pedal, 26 dollar part at the dealership, but 100 for labor!?! I would look at that first, very common problem.

buckmeister2

I have the same issue with cruise control...light comes on dash, but does not engage. all brake lights work as they should. The answer about replacing the brake light switch requires knowing if you guys had brake lights working before you replaced the switch.

If your cruise did not work, and you had no brake lights, that is a no brainer. If you fixed the cruise by replacing the brake light switch, did you have brake lights before you replaced the switch??? If you can tell me for sure that you had brake lights, but the replacement of the switch fixed the cruise, then I will buy the switch and install it. thanks in advance for your help.

jim

f5fstop

Brake lamp switch has four terminals so part of the switch could go bad and still have stop lamps.
Terminal A signal to ECM/BCM
Terminal B 12 volt reference from battery
Terminal C 12 volt reference from BCM
Terminal D trigger control to BCM

When you step on the stop lamp switch, an internal switch closes that allows 12 volts (terminal B) to flow to the ECM and BCM. This dual signal is used as a dual control to make sure the cruise is disabled if the stop lamp switch is closed (brake applied). That way if one signal fails there is another signal via another circuit. When the ECM sees this signal it deactivates the cruise control; when the BCM sees this signal it notifies the ECM via the serial data bus to disable cruise (redundancy)

The other two terminals are used for brake lamp control. When this switch is closed due to the brakes being applied, voltage from terminal C flows through the switch to terminal D, back to the BCM and this signals the BCM to turn on the brake lamps.

So, conceivably you COULD have a failed internal switch thus signaling the brakes pedal is depressed when it is not.

Or, it could be an adjustment to that switch assembly.

OR, it could be a screwed up ECM calibration as the following bulletin will attest to (although to me it sounds like a park lamp switch, but HONESTLY, I cannot say for sure, as no one else can, without full diagnostics):

#09-08-68-001: Cruise Control Turns Off During Operation (Reprogram ECM) - (Nov 13, 2009)


Subject: Cruise Control Turns Off During Operation (Reprogram ECM)


Models: 2008-2009 Cadillac Escalade, Escalade ESV, Escalade EXT

2007-2009 Chevrolet Silverado

2008-2009 Chevrolet Avalanche, Suburban, Tahoe

2007-2009 GMC Sierra

2008-2009 GMC Yukon, Yukon Denali, Yukon XL, Yukon Denali XL

2008-2009 HUMMER H2




--------------------------------------------------------------------------------
Condition
On rare occasions, some customers may comment that the cruise control turned off. This typically occurs during operation and while pulling up and releasing both driver door window switches or activating the heated windshield washer fluid system in cold weather conditions with a battery charge below 80%.

Cause
Cruise control command cancellation is caused by a voltage spike that occurs when the driver door window switches are released or when the heated washer fluid system is activated.

Correction
A revised calibration has been developed to address this condition. Technicians are to reprogram the ECM with the latest calibrations available. This new service calibration is available on TIS2WEB using the Service Programming System (SPS). Refer to the SPS procedures in SI. SPS may require the technician to select the calibration from the ECM calibration screen.

Note: This calibration update should only be used when this loss of cruise control condition is experienced.

When using a Tech 2® or a multiple diagnostic interface (MDI) for reprogramming, ensure that it is updated with the latest software version.

During programming, the battery voltage must be maintained within the proper range of 12-15 volts. Only use the approved Midtronics® PSC 550 Battery Maintainer (SPS Programming Support Tool EL-49642) or equivalent during

f5fstop

Honestly, is this all you contract guys at GM's customer assistance center can say? ..."encourage you to consult with a certified technician...."
And the master cylinder pressure sensor/EBCM have me sitting pondering the expression WTF!

MCC35

Jim,
In answer to your question yes my brake lights worked.
I do not know of a diagnostic way to check the switch while it's on the vehicle, however I would think if you remove the switch and checked resistance between the poles that may give some indication if the 1 portion of it is not working.
For my problem it was intermittent at first. So one time while driving and it would not re-engage I pushed the resume speed button, and the cruise did not engage. I felt it was odd for two buttons to go at the same time yet the "On/Off" still worked. I decided to take a chance and buy an inexpensive part first and it worked.
MCC35

chris50317

Ok you guys most likely do not need a new brake light switch, might be good idea to make sure you can get a new clip (dealer only part) that holds the switch to the brake pedal.This clip tends to fly a way to never never land. I call it the HOUDINI clip





On my 2008 Silverado the light for cruise control would come on but would not set. I took off the brake light switch as suggested here. Greased the switch adjusted the switch so brake lights work correctly. Went for test drive and the cruise was not working so about a week later (after grease worked into place) the cruise started to work.