What would prevent Cruise Control from working?

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07-04-2016
TXjeepTJ

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What would prevent Cruise Control from working?

I have a 2005 LQ4 complete pullout w/ the 4L80E it came with and PCM. It is a DBW, and the psi conversions wiring harness I used has inputs for the "Cruise on/off" "Set/coast" "accelerate/resume". I wired everything in - and using the HPTuners "Status Bits" I can see that the PCM is getting the "On/Off" signal - and also getting the "set" and "resume" functions whenever I push the momentary buttons.

But the Cruise Control does not work - meaning when I flip the "on" switch and push the "set" button - which the PCM is recognizing all these functions - it does not lock in on a speed and maintain it.

On the "status bits" I have one input called "Cruise Lockout" which shows "LOCKOUT" highlighted in green the entire time. So I'm guessing some other function, besides the wiring, is preventing cruise from working.

What are the functions that would cause cruise to "lockout"? It is also getting the brake signal, so it can't be that one..

"Cruise brake switch" always says on.. not sure what that means - and what the difference is between that and cruise brake pedal"

I attached a scan of me toggling through the buttons while driving.. take a look if you could so you can see the status bits

Attachment 60618 Attachment 60619
07-04-2016
Jon S.

Sounds like things are not wired correctly. With a DBW P59 PCM, the TAC Module receives only one brake input (Cruise Control Brake Switch) - while the earlier DBC Cruise Modules received two brake inputs.

The switch on the OEM brake pedal has two inverse functions.

The PCM needs 12 volts when the brakes are not applied (for TCC lockup). This 12 volts to the PCM is then interrupted when the brakes are applied - which unlocks the TCC.

The TAC Module needs 12 volts when the brakes are applied (for Cruise Control disengagement).

Guessing that things have been wired such that the PCM and the TAC Module are both getting 12 volts when the brakes are not applied.
07-04-2016
TXjeepTJ

Quote:

Originally Posted by Jon S.

Sounds like things are not wired correctly. With a DBW P59 PCM, the TAC Module receives only one brake input (Cruise Control Brake Switch) - while the earlier DBC Cruise Modules received two brake inputs.

The switch on the OEM brake pedal has two inverse functions.

The PCM needs 12 volts when the brakes are not applied (for TCC lockup). This 12 volts to the PCM is then interrupted when the brakes are applied - which unlocks the TCC.

The TAC Module needs 12 volts when the brakes are applied (for Cruise Control disengagement).

Guessing that things have been wired such that the PCM and the TAC Module are both getting 12 volts when the brakes are not applied.

It looks like you may be correct. I ran through the instructions for the wiring harness, and there is a yellow wire that I have not hooked up that goes to "12 volts when brakes are applied".. Will hook this up and will report back!