Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner

cruise control

23K views 48 replies 18 participants last post by  chemengr79 
#1 ·
Hey guys, i just recently changed my front left wheel bearing, and now my cruise control has a mind of its own! lol it shuts off randomly, sometimes working for a few seconds before shutting right back off, and other times working for a while!

Any suggestions?
 
#3 ·
Intermittent cruise control issues are very difficult to diagnose, and your wheel bearing replacement probably has nothing to do with it. Check your brake pedal for having a hair trigger.

The computer has a special memory that only a dealer's scan tool can access, that stores the last few REASONS why the cruise control disconnects. Like the brake signal or the multifunction switch. You might need to pay them to look into this special memory.
 
#5 ·
Same Issue...

I'm having the same issue...as described in another thread, my cruise works flawlessy up to 64mph...if I attempt to set a speed above that, the cruise control disengages randomly. Interestingly, I also began having this issue immediately after having a front left hub assembly replaced @ the dealer a few weeks ago...
 
#6 ·
One of the inputs for cruise, is from the VSS (vehicle speed sensor), via the PCM.

I know you just changed a front wheel hub; and, the wheel hub, contains one of the ABS sensors.

In the older trucks (sub 06, I think) the ABS is 3 channel; one on each front wheel, and the 3rd uses the VSS.

I don't know if there is a connection, but there appears to be a possibility.

But, as has been suggested, the only way to properly test is with a special scan tool at the dealers.
 
#8 ·
Nope, only if it was the rear channel (I think).

But, if any of the 3 are not, as you say "connected or relaying info correctly" it would light the ABS light on the dash.

Which might stop the cruise from working :undecided; but, your light is not on.
 
#10 ·
I am having the same issue as stated above. I just replaced the front wheel hub which came with a new sensor wire and now my cruise control is intermittent. I am going to check the connection first then possibly pull the old sensor wire off of the the old hub and see if that is the issue.
 
#11 ·
Here is how the cruise works, and what affects it. Pay particular attention to what causes it to disengage.

CRUISE CONTROL DESCRIPTION AND OPERATION

Cruise control is a speed control system that maintains a desired vehicle speed under normal driving conditions at vehicle speeds above 40 km/h (25 mph) . Steep grades may cause variations in the selected vehicle speeds.

The following are the main components of the cruise control system:

* The powertrain control module (PCM)
* The On/Off switch
* The Resume/Accel switch
* The Set/Coast switch
* The torque converter clutch (TCC) brake switch
* The stop lamp switch
* The throttle actuator control (TAC) motor
* The vehicle speed sensor (VSS)

Cruise Control Engaged
The cruise control system will engage and adjust the vehicle speed based on the activation of the following cruise control switches:

* On/Off
* Resume/Accel
* Set/Coast

The cruise control switches are located on the multifunction/turn signal lever.

The powertrain control module (PCM) monitors the signal circuits of the cruise control switches in order to determine when to capture and maintain the selected vehicle speed. The PCM uses the throttle actuator control (TAC) module motor in order to control the vehicle speed. For further information on the TAC system, refer to Throttle Actuator Control (TAC) System Description in Computers and Control Systems - 4.2L.

Ignition positive voltage is supplied from the 10-amp HVAC 1 fuse to the cruise control switch via the ignition 3 voltage circuit. When the normally open cruise control On/Off switch is turned ON, the switch closes and the PCM detects a high signal voltage on the cruise control on switch signal circuit. When the normally open Set/Coast switch is pressed, the switch closes and the PCM detects a high signal voltage on the cruise control set/coast switch signal circuit. To engage the cruise control system, turn the On/Off switch ON and momentarily press the Set/Coast switch. The PCM will confirm that the cruise control enable criteria has been achieved. The PCM will engage the cruise control system and record the selected vehicle speed. The PCM sends a class 2 message to the instrument panel cluster (IPC) in order to illuminate the cruise control indicator. Pressing the accelerator pedal, while the cruise control system is engaged, will allow the driver to override the cruise control system in order to accelerate the vehicle beyond the current set vehicle speed. When the accelerator pedal is released, the vehicle will decelerate and resume the current set vehicle speed. The driver can also override the current set vehicle speed via the Set/Coast switch and the Resume/Accel switch. When the cruise control system is engaged, pressing and holding the Set/Coast switch will allow the vehicle to decelerate from the current set vehicle speed without deactivating the cruise control system. When the Set/Coast switch is released, the PCM will record the vehicle speed and maintain the vehicle speed as the new set vehicle speed. When the cruise control system is engaged, momentarily pressing the Set/Coast switch will allow the vehicle to decelerate at 1 mph increments for each time that the Set/Coast is momentarily pressed, with a minimum vehicle speed of 23 mph . When the normally open Resume/Accel switch is activated, the switch closes and the PCM detects a high signal voltage on the cruise control resume/accel switch signal circuit. Activating and holding the Resume/Accel switch, when the cruise control system is engaged, will allow the vehicle to accelerate to a greater vehicle speed than the current set vehicle speed. When the Resume/Accel switch is released, the PCM will record the vehicle speed and maintain the vehicle speed as the new set vehicle speed. When the cruise control system is engaged, momentarily activating the Resume/Accel switch will allow the vehicle to accelerate at 1 mph increments for each time that the Resume/Accel switch is momentarily activated, with the maximum acceleration total of 10 mph over the current set vehicle speed. Momentarily activating the Resume/Accel switch, after the cruise control system has been disengaged by pressing the brake pedal, will recall the previous set vehicle speed that is recorded in the PCM.

Cruise Control Disengaged
The powertrain control module (PCM) disengages the cruise control operation based on the signals from the following switches:

* The On/Off switch
* The torque converter clutch (TCC) brake switch
* The stop lamp switch

The TCC brake switch and the stop lamp switch are incorporated into an assembly and are mounted to the brake pedal bracket. Pressing the brake pedal while the cruise control is engaged will disengaged the cruise control system. The PCM monitors the TCC brake switch/cruise control release signal circuit and the stop lamp switch signal circuit. When the brake pedal is pressed, the normally closed TCC brake switch opens and the normally open stop lamp switch closes. The PCM detects a low signal voltage on the TCC brake switch/cruise control release signal circuit and detects a high signal voltage on the stop lamp switch signal circuit. The cruise control system will disengage when the cruise control On/Off switch is turned OFF. The vehicle speed stored in the memory of the PCM will be erased when the cruise control On/Off switch is turned to OFF, or the ignition switch is turned OFF.

The cruise control system will disengage when the PCM detects that the driver has the accelerator pedal override active for approximately 60 seconds.

When the cruise control system is disengaged, the PCM sends a class 2 message to the instrument panel cluster (IPC) in order to deactivate the cruise control indicator.

Cruise Control Inhibited
The powertrain control module (PCM) inhibits the cruise control operation when any of the following conditions exist:

* The PCM detects that the center high mounted stop lamp (CHMSL) is not operating properly.
* A cruise control system related DTC has been set.
* The vehicle speed is less than 40 km/h (25 mph) .
* The vehicle is in PARK, REVERSE, NEUTRAL, or 1st gear.
* The engine RPM low.
* The engine RPM is high.
* The vehicle speed is to high.
* The system voltage is not between 6-16 volts .
* The antilock brake system/traction control system (TCS) is active for more than 2 seconds.



So, your cruise could turn off if:
  • Your CHMSL is lighting when it shouldn't.
  • The switch is bad internally, and it's "turning off" when it shouldn't.
 
#12 ·
So, your cruise could turn off if:
  • Your CHMSL is lighting when it shouldn't.
  • The switch is bad internally, and it's "turning off" when it shouldn't.
Well, there is nothing unique about the 3rd brake light.
It operates from the same switch contacts as the side brake lights.

However, I agree, if any brake light is operating when it should not, the cruise will dis-engage.

We have said, all along, that a faulty brake pedal switch can cause cruise failure.

However, in all reported occurances, the one common factor is that there was a front wheel hub changed.

BUT NO ABS LIGHT :undecided
 
#14 ·
And the front wheel hub change may have to do with the PCM seeing a wheel rotating less than 25mph, thus inhibiting the cruise engagement. I can look more at the wiring diagrams tomorrow at work.
Sorry, the PCM gets its speed info from the VSS (vehicle speed sensor) mounted in the transfer case on 4x4 trucks, or in the tranny tail piece on 2 wd trucks.

The front hubs are only for ABS (and perhaps traction control) speed sensing.

I do not, however, understand what the torque converter clutch has to do with it and/or what connection it has to the brake pedal position switch.

I do think, there may be a connection with the traction control circuits.
But not sure what at this time.
 
#15 ·
Sorry, the PCM gets its speed info from the VSS (vehicle speed sensor) mounted in the transfer case on 4x4 trucks, or in the tranny tail piece on 2 wd trucks.

The front hubs are only for ABS (and perhaps traction control) speed sensing.

I do not, however, understand what the torque converter clutch has to do with it and/or what connection it has to the brake pedal position switch.

I do think, there may be a connection with the traction control circuits.
But not sure what at this time.
Don't apologize. When you depress the brake pedal, the TCC immediately disengages lockup. My guess is that so that when you accelerate, there is no "down-shift" delay.

I'll investigate the diagrams tomorrow.
 
#18 · (Edited)
Chill pal, I'm not looking for a fight, just trying to fix this poor SOB's cruise control problem.

We are talking about the same thing.
When I said that the PCM receives a signal from the brake pedal switch, I'm talking about pin c, the purple wire.

The PCM can do a number of things with this signal.
It turns off the cruise control
It also unlocks the the TCC.

These are two separate circuits, simply triggered by the same input.

One does not impact the other; however, failure of the common input will fail both.

I simply maintain, that it is confusing to reference one when we should be talking about the other.


I'm sure, that if we (two knowledgeable people) work together, we can solve this problem that now appears to be affecting a number of members.
 
#22 ·
Not to bring up an oldish thread, but I wanted to add a few notes. I also replaced both front hubs shortly before beginning to notice the same cc issues as the OP. I wonder if it has anything to do with the calibration of the hub assembly. around the same time, I had a flat, and ran the spare for a short period (2 days or so). The spare was a different size than the 4 original tires, larger, if I recall. I then put 4 new tires on, of the same size that were on the vehicle. It was soon after this that I noticed the CC issue occuring. I could see wheel size being an issue with TC, especially if there was a mismatch, but I would think the problem would go away once the tires matched again, and were original size.

I cannot find any way to calibrate sensors in the hub assemblies, but I did notice a Jegs chip for $300 or so that also allows you to recalibrate the speedo for wheel size changes. Does anyone have any opinions on whether that would work? Or anything else I have posted. I just did a 3.5 hr trip and the cc kicked off 18 times. very annoying. The odd part is I have made longer trips and never had the cc disengage once... also of interest, is the faster you set the CC to, the more common the problem. around 77 or so, the cc will disengage after a few minutes. I haven't ever had it happen below 70mph.

I'm a speed freak, and drove a LOT, so just drive slow is not gonna work for me :)
 
#25 ·
Changing all 4 tires to the same size wouldn't effect your cruise control anyway, only if 1 wheel was off size, making your comp think one wheel was spinning faster than the others, ie slipping.

We really need to get someone familiar with the conditions which cause the cc to disengage during normal operation (wheel slip being one of them), and then try and figure out what causes the condition to happen as intermittently as it does.

Do you know what bearing brand was used when you replaced yours? I think mine were national bearing. From what I know, the cruise control receives wheel speed signal from 3 sensors on the truck, each fron wheel, and one from the rear end. If either of these is sending wrong information, it would cause the cc to disengage, however it doesn't make sense that it would happen intermittently.

Alternatively, there could be a faulty control module somewhere, but someone familiar with the whole cc system would need to chime in to shed some light on where to look.

It seems odd that all of the people who have reported this problem notice it after changing a wheel bearing.

My father is a salesman at a GM dealer and he's asked the service techs and they did not nave any suggestions. I've got a hanes manual, I'll try reading up on the CC system a bit. Maybe I can come up with somewhere to look.
 
#27 ·
My father is a salesman at a GM dealer and he's asked the service techs and they did not nave any suggestions.
Goofy techs. The shop manual says that the PCM has a special memory for keeping track of the last few reasons that the CC was turned off or suppressed. There are 6-7 things that can kill the CC function, and I've posted them in previous discussions of the system. But intermittent issues are so hard to track down that the GM designers put in the code to keep track of the issues so a Tech II scan tool could interrogate them.

Get the techs to put the Tech II tool to work and look at CC memory.
 
#29 ·
Hi all! This is my first post, but I have browsed the forums for a while now.

Not to bring to life an old thread, but I too, am having the same problem with my CC. I noticed it after I had the left front wheel bearing replaced. What exactly is the cause of this and, more importantly, how do I fix it? I read the entire post, but did not notice the answer. Thanks!
 
#30 ·
...What exactly is the cause of this and, more importantly, how do I fix it? I read the entire post, but did not notice the answer. Thanks!
Did you read the entire thread to see there IS NO one answer? If you don't have a SES or ABS light on, you may have to work through all the other possible causes of CC suppression, and possibly pay a dealer to interrogate the PCM memory. Good luck. We'll love to hear back if you have a different cause than the ones that have been listed.
 
#31 ·
Ghost in the Machine

My CC has been shutting itself off since I had the instrument panel replaced in Jan 2010 due to the speedometer registering 0mph while I was doing 75mph.
Yesterday :suicide::bonk: my vehicle was at the dealer all day and the dealer was perplexed! Everything they tried (based on forums from this site.. thank you) turned out to be NOT the cause of my problem. Finally at the end of the day they gave me a 50/50 conclusion that it was the multi function switch.The dealer tested the replacement switch a few times and the CC stayed on. I picked up my vehicle drove it 10 minutes on the freeway CC worked fine. I drove it on another freeway and the CC shut itself off twice. I called the dealer who was very shocked to hear me complaining about the same issue again. The dealer has attached my vehicle to the Tech II scanner and the readout was a possible wheel traction issue, however the wheel traction sensors are working fine. The dealer also put a new computer inside my vehicle thinking they could trick the CC into working, no such luck. The mechanic called GM tech support and GM tech support didn't have a definitive answer. The PCM ,computer and wheel traction /speed sensors are all fully operational without any issues. The SES light doesn't come on when the CC shuts itself off.
The dealer seems at this time to be dedicated to finding the cause, as of today I'm awaiting a call back with some more answers.
 
#32 ·
My CC has been shutting itself off since I had the instrument panel replaced in Jan 2010 due to the speedometer registering 0mph while I was doing 75mph.
Instrument cluster problems can't cause CC suppression. The gauges are a display only unit and you can drive the vehicle just fine without it. Must have been something they bonked while doing that work.
Yesterday :suicide::bonk: my vehicle was at the dealer all day and the dealer was perplexed! Everything they tried (based on forums from this site.. thank you) turned out to be NOT the cause of my problem. Finally at the end of the day they gave me a 50/50 conclusion that it was the multi function switch.The dealer tested the replacement switch a few times and the CC stayed on. I picked up my vehicle drove it 10 minutes on the freeway CC worked fine. I drove it on another freeway and the CC shut itself off twice. I called the dealer who was very shocked to hear me complaining about the same issue again. The dealer has attached my vehicle to the Tech II scanner and the readout was a possible wheel traction issue, however the wheel traction sensors are working fine. The dealer also put a new computer inside my vehicle thinking they could trick the CC into working, no such luck. The mechanic called GM tech support and GM tech support didn't have a definitive answer. The PCM ,computer and wheel traction /speed sensors are all fully operational without any issues. The SES light doesn't come on when the CC shuts itself off.
The dealer seems at this time to be dedicated to finding the cause, as of today I'm awaiting a call back with some more answers.
The dealer doesn't know that there is a special location in the engine computer memory that RETAINS the reasons for the last few times the CC is turned off? The CC system is difficult to troubleshoot, so the designers included this troubleshooting tool. If the CC turns off because of a flaky switch, it remembers. If it turns off because of a SES code, it remembers. If it turns off because you're speeding out of control down a 30 degree mountain hill at 100 MPH, it remembers. If it's overheating, has an ABS code, or any of a dozen reasons, the computer memory retains a clue.

How can the dealer NOT know this and find a fix in ten minutes? :weird:

My personal guess - you have a hair-trigger brake light pedal switch that's going off due to bumps in the road. That also suppresses the CC. You can try this at home.

Oh, wait - did you say the dealer was reading posts HERE? :dielaugh: :dielaugh: :dielaugh:
 
#33 · (Edited)
Thanks for the reply and suggestion.
The brake line has been checked, I even checked it myself. The cruise will shut itself off on a smooth paved road with no wind resistance or incline.

and in NO way was the dealer reading this website.. LOL.. I printed what I found here and took it to them!

The dealer did check the memory as suggested in previous postings.. and the only thing it showed was the wheel traction was off, however as I said earlier the wheel traction sensors were checked and are in good working order.

I didn't think the instrument panel was the cause, I just was giving history ,grasping at straws!

:crazy:
 
#34 ·
Just finished talking to the service mgr at the dealership.

He says after talking to the GM guru's they still have no difinitive answer what the cause can be. So the plan now is to replace the brake switch tomorrow afternoon and drive it and report back to the dealer the next morning.

Wish me luck!!
;):duh:
 
#35 ·
How much do we buy new GM products for? How much does a GM engineer or techincian make?

Dealer installed a new brake switch this afternoon, drove on the freeway at speeds of 75, 70,. 69, 65 (20min total on freeway) , cruise shut off four times. :hopeless

Does anyone have the answer?!?!?!?
 
#36 ·
A lot of things will turn off cruise control; one of my theories, is the reluctor ring on the front wheel bearing hub.

If your truck had one of the front hubs changed because the wheel bearing had gone bad, that may be the cause.
Some of the after market hubs may, I say may, have a reluctor ring that is slightly different in size that the OEM on the other corner. :m2:
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top