No cruise control

[Racerrich08]

Hi I have a 03 lb7 and I cant figure out what's wrong with my cc
I watch it on my snapon scanner shows the on /off is working the accel and deaxcel is working and that the set button is working but where it says cc engaged it says no and I replaced the break switch please help me figure this out. I do a lot of highway driving

 

[Stingpuller]

Cruise control

Does it by chance have LED tail lights?

 

[Racerrich08]

No LEDs lighs

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[RickDLance]

Any codes? Sometimes a code can cause the cruise not to works?

 

[Racerrich08]

No codes

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[TheBac]

Moved to LB7 section

 

[snowman22]

I would expect a code, but are all the wheel speed sensors reading near the same accurate value?

 

[Racerrich08]

Yes they are

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[darkness]

Pull any fuses for the trailer plug and see if that fixes it.

 

[Racerrich08]

I unplugged it from the back

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[Chevy1925]

You need to check every single fuse under the hood and inside

 

[Racerrich08]

I did inside and outside of truck

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[dndj]

I did inside and outside of truck

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FSM says the ECM inhibits cruise control operation when any of the following conditions exist:

• A cruise control module DTC (trouble code) is set
• Vehicle speed < 25mph
• Vehicle is in Park, Neutral, Reverse, or 1st gear
• Engine RPM is low
• Engine RPM is high
• Vehicle speed is too high
• System voltage not between 12 and 16v DC
• ABS/traction control active for more than 2 seconds

Maybe one of these things is sending a false or erroneous signal to the cruise unit. Not real helpful of GM to describe what "too low" or "too high" means either.

 

[Racerrich08]

I'm going to get a wiring diagram in the morning

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[dndj]

Schematic

Here you go. Let me know if you want the ABS schematic too which includes the brake light/TCC switch combo on the pedal.

 

[TheBac]

Last time batteries were replaced? Condition of alternator/charging system?

In real operation, does the CC initially work then immediately disengage or it wont engage at all?

 

[Stingpuller]

CC

Have lift up on the brake pedal as your trying to set the cruise? I have seen the switch cause a problem but the brake lights still work fine.

 

[Benny315]

Have lift up on the brake pedal as your trying to set the cruise? I have seen the switch cause a problem but the brake lights still work fine.
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OP says he replaced brake switch... I would check in the steering column next,,, Check the "Tow haul" wire has not broke/rubbing and also the cruise/signal wires as well.

 

[Bdsankey]

OP says he replaced brake switch... I would check in the steering column next,,, Check the "Tow haul" wire has not broke/rubbing and also the cruise/signal wires as well.

I'd imagine if the cruise control wiring was damaged in the column that the ECM wouldn't be seeing accurate button movements on the stalk but I have seen wiring do some crazy stuff. That's reason #1 I hate trying to diagnose wiring problems.

 

[Benny315]

I'd imagine if the cruise control wiring was damaged in the column that the ECM wouldn't be seeing accurate button movements on the stalk but I have seen wiring do some crazy stuff. That's reason #1 I hate trying to diagnose wiring problems.

Yeah, wiring issue's can be a PITA... I had an issue with my tap shift/tow haul wire causing odd tranny shift and no cruise either.. A broken wire that is not completely broke or hanging on by a thread can show on the scanner as working, but the amp/volts required may not be met. Just tryn to help..