Cruise Control Failed

[ComputernerdBD]

Hey everyone, well I found tonight that my cruise control simply is not working at all. No light, no throttle takeover. I have tried to troubleshoot based on some information on the site here but here are the recent changes that have been made on the truck:

1. LED taillight conversion with a Novita LM487 LED flasher and Phillips 3157 LEDs in the stop and turn lights in the rear.
2. Oil change
3. Serpentine belt replacement
4. Replace transmission cooler lines
5. Tire rotation
6. Throttle body cleaning

Now based on information on the site, I have backed out of the LED replacement and put the normal bulbs back in temporarily but that did not solve it. No bulbs are out in the back of the truck, including the center high mounted stop light. I tested the brake lights and they do work normally. I scanned for codes and nothing. The only other thing wrong with the truck which I have not bothered to fix yet as this happened last week is a failed TPMS sensor, therefore I get a "Service Tire Monitor" alert on the dashboard. Is the TPMS system one of the triggers for disabling the cruise control? Which fuses should I also be checking, I realize that it may or may not be like my 98 Jimmy which has a dedicated cable driven module for that but the Trailblazer is fly by wire. Thanks

 

[budwich]

does the brake switch work? the brake light working is one test but I think there are three contacts, perhaps one is not function.... meter to see if you get contact changes on all contact points.
I believe any kind of "maintenance warning" causes the system to disable cruise control.

 

[Mooseman]

Some PCM codes, even pending, will kill the cruise, including P1345. Check for any pending codes.

I attached the printout from GM-SI regarding the cruise control and its operation, including what prevents it from working.

 

[Sparky]

There is the possibility that the brake switch is the culprit. I know you said that your lights work fine, however, there are two sets of contacts on the switch. My Silverado for example the lights worked normally but I couldn't set the cruise without kicking the side of the pedal, or pulling upward on it with my foot. Then of course it would randomly shut off because it thought I stepped on the pedal. New brake switch fixed it.

 

[Blckshdw]

1. LED taillight conversion with a Novita LM487 LED flasher...

The flasher module is your problem. This is a known issue with the LM487 from years back, a newer LM486 (I don't understand why the model # is lower...) is supposed to resolve the cruise control issue.

For those of us who have the LM487 and still have working cruise control (I am one of them) we all happen to have manufactured LED tail lights with built in load resistors.

 

[ComputernerdBD]

No pending PCM codes but with the flasher: Ok now it makes sense.... I got the LM486 today along with switchback LEDs for the turn signals up front and 194 amber LEDs for the side markers and mirror flashers. I will replace it tomorrow and report back.

Also with the tire warning: I went to the tire shop twice today. They say all the sensors are reporting OK and they reset/relearned the system twice along with setting tire pressure but after about 20 miles both times the light and reading dropout on one tire came back.... Cruise control was still not working when the light was off so it appears no relation between the TPMS and cruise anyway. The tire shop recommended going to the dealer (which I am completely against) to find out about a reflash but thoughts on alternatives??? Maybe the sensor really is bad? Thanks

 

[budwich]

you didn't indicate if you tested the brake switch. On tpms, are you running any "wireless" stuff that transmits to the radio or equivalent?

 

[Sparky]

could be a bad sensor battery, since your vehicle is now 9 years old. TPMS sensor batteries lifespan is estimated 6-8 years IIRC

 

[budwich]

pull the connector for the multi-function switch and see if you are getting the "activation / on" from the switch on the stock arm.

 

[ComputernerdBD]

No wireless mess in the truck other than my phone. I did replace the flasher with an LM486 due to the known issue with the LM487 and installed my switchbacks in the parking lights and 194 amber LEDs in the side marker and mirror lights due to the lower wattage rating of the LM486 (I was planning on replacing those anyway, just expedited it).

With the TPMS, I decided to pull a trick from my job in IT and just reboot the module. I figured based on the way it was acting maybe it was throwing errors internally caused by old code that can be fixed with a reboot (much like an old Windows box that has been online for too long). I pulled both fuses listed for the liftgate module and now suddenly it is seeing all 4 sensors without issue and it has been working fine. If it is running an obsolete version of code for that module, so be it. It worked 10 years without an issue like this. Hopefully it stays that way so I don't have to pay a dealer all my overtime this week to fix it.

I was not able to figure out the brake light switch but because I had the same problem at around the same mileage and age on my other truck I decided to get the part. Even if I didn't isolate it to that, I am going to need it anyway eventually.

After the flasher module replacement and light install, no go with the cruise control at first. I then tried to back out of the LED stop lights to see if that fixed it before I drove it to the dealer to buy the part. Still no. Funny thing was I tried it again and the cruise control suddenly started working properly on the way back home from the dealership. I put the LEDs back in and did a test drive. Has not failed since. Maybe a silent code that cleared itself out later after driving it? Maybe the TPMS system did cause a problem? It seems at least the flasher module was for sure it at the minimum but possible secondary failure.

Now new question: What do I do with the LM487? Will it work in the S10 series trucks and if yes will it cause the same computer problems with the cruise control even with it being a separate module without the fly-by-wire throttle? Thanks again for the tips.

EDIT: Please disregard the last part, I can see the flasher in the S10 series is a much smaller design. I will keep the LM487 in the back of the truck as a spare in case of any future problems. Not the first time I have replaced parts and then needed a spare down the road, pun intended. LOL

 

[fj4072]

No wireless mess in the truck other than my phone. I did replace the flasher with an LM486 due to the known issue with the LM487 and installed my switchbacks in the parking lights and 194 amber LEDs in the side marker and mirror lights due to the lower wattage rating of the LM486 (I was planning on replacing those anyway, just expedited it).

With the TPMS, I decided to pull a trick from my job in IT and just reboot the module. I figured based on the way it was acting maybe it was throwing errors internally caused by old code that can be fixed with a reboot (much like an old Windows box that has been online for too long). I pulled both fuses listed for the liftgate module and now suddenly it is seeing all 4 sensors without issue and it has been working fine. If it is running an obsolete version of code for that module, so be it. It worked 10 years without an issue like this. Hopefully it stays that way so I don't have to pay a dealer all my overtime this week to fix it.

I was not able to figure out the brake light switch but because I had the same problem at around the same mileage and age on my other truck I decided to get the part. Even if I didn't isolate it to that, I am going to need it anyway eventually.

After the flasher module replacement and light install, no go with the cruise control at first. I then tried to back out of the LED stop lights to see if that fixed it before I drove it to the dealer to buy the part. Still no. Funny thing was I tried it again and the cruise control suddenly started working properly on the way back home from the dealership. I put the LEDs back in and did a test drive. Has not failed since. Maybe a silent code that cleared itself out later after driving it? Maybe the TPMS system did cause a problem? It seems at least the flasher module was for sure it at the minimum but possible secondary failure.

Now new question: What do I do with the LM487? Will it work in the S10 series trucks and if yes will it cause the same computer problems with the cruise control even with it being a separate module without the fly-by-wire throttle? Thanks again for the tips.

EDIT: Please disregard the last part, I can see the flasher in the S10 series is a much smaller design. I will keep the LM487 in the back of the truck as a spare in case of any future problems. Not the first time I have replaced parts and then needed a spare down the road, pun intended. LOL

Hello, lm486 says 2 signal and 4 hazzard. My question is, WITH LED's present in all turn signals front and back, will this work?