Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner
1 - 10 of 10 Posts

·
Registered
Joined
·
18 Posts
Discussion Starter · #1 ·
Not sure what is going on but here is the issue. If i set the cruise control at or below 75mph it works perfectly, no issues at all. If i set it at 77mph or above it'll work for 20-30 seconds then disengage (cruise light turns off as well) if i hit the resume button, it re-engages and away i go again for 10-15 seconds then the same thing. If i then slow down to 75mph and hit set again it is fine, no issues.
I have no SES or check engine lights on (or any other cluster lights), i checked for any codes and there are none. my brake lights are all working fine....i just can't figure out what it could be.

Any ideas? Thanks in advanced,

michtb
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #2 · (Edited)
any idea's or do i have everyone stumped?
One additional bit of info, i do not have any aftermarket LED lights (in case anyone was wondering)

Thanks,

michtb
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
1,708 Posts
I have never tried to set mine above 65. Did yours ever work above 75? Could be a safety feature.
 

·
Registered
2003 gmc envoy_slt
Joined
·
357 Posts
The Factory repair manual just says the cruise control will be "inhibited when the speed is too high" but doesn't say what "too high" is. However, I once had a Cadillac that sounded an alarm and displayed a "Speed too high" message when speed was 75. Turned out that the vehicle had been built to certain foreign specs which required this. Saudi Arabia was one of the countries.

I don't recall ever setting mine at 75 or above but the next time I'm out on a highway that allows it, I'm going to give it a try.

C.B.
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #5 ·
before the issue i would regularly (every morning) set it to 78 or 79 on the highway on my way to work with no issues. I have set it at 85 a few times on long trips if i had the radar detector up.
Some additional info, i've got 64K miles on it and i cleaned the throttle body yesterday hoping that would fix it, no such luck. at least it runs a bit smoother after the cleaning (not that it was running very rough before that).

my haynes repair manual says there is a speed sensor in the tranny or rear differential, anyway to test to see if that is the issue? and which is it actually in? tranny or rear diff?

Thanks,

michtb
 

·
Banned
2004 gmc
Joined
·
26,181 Posts
If you have a 4X4 it's on the back end of the transfer case. But if the speedo reads properly, then the sensor's OK.

Are you getting proper TCC lockup? The brake pedal has two switches. One for the brake lights and one to disable the torque converter clutch. Either one of these having a hair-trigger could disable the cruise control at odd times.
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #7 ·
If you have a 4X4 it's on the back end of the transfer case. But if the speedo reads properly, then the sensor's OK.

Are you getting proper TCC lockup? The brake pedal has two switches. One for the brake lights and one to disable the torque converter clutch. Either one of these having a hair-trigger could disable the cruise control at odd times.
i believe so, everything feels right when i'm going highway speeds, i don't know what it would feel like if the TCC lockup wasn't happening...
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #9 ·
You can detect TCC lockup in the RPM and a slight bump.
Well here is some more info, on my way into work this morning i set the cruise at 80 and it was fine, after about 5 minutes i started going up a hill and the transmission shifted to help go up the hill, the RPM climbed to just slightly under 3000RPM when this occurred. After about 10 seconds at close to 3000RPM it disengaged the cruise, right after the hill i re-set the cruise until the next hill and the exact same thing happened...so it seems to be RPM related...

Keep in mind this is the same road i've driven down the last 5 years and this just started happening, this never occurred on these same hills in the past.
 

·
Banned
2004 gmc
Joined
·
26,181 Posts
Try it in 3rd gear, some speed that would give you 3000 RPM on flat terrain. I'm also guessing it may be vibration related to RPM that is kicking off the cruise control. If it worked in the past, it still might be a slight increase in vibration causes a hair-trigger brake pedal switch to trip it off.

You can also try that on the flat road in 4th gear. Get cruise working, then see how light a touch on the brake pedal it takes to trip off the cruise.

If all else fails, get to the dealer or a GM specific independent mechanic, where a high end tech tool can interrogate the PCM and ask it for the REASONS for the last 8 cruise control disengagements. There's a list of about 40 events that can force a disengagement, and it may be essential to know what's causing it before going down 40 different troubleshooting paths.
 
1 - 10 of 10 Posts
Top