My brake lights come on anytime they want to and won't go off. I replaced the sensor under the brake pedal and replaced the wires and still have problems. At times when the lights are on and I step on the brake pedal they go off and then you can't tell that I'm on my brakes. Any ideas what the problem is ??? Took to several places but nobody can figure out what's wrong.

 

Welcome!

Which wires?
Does the CHMSL (third stop light) act the same way?
What year is the HHR.
Did something happen just before this started? Somebody installing something electrical, somebody working under the hood, somebody replacing the radio etc?

 

Replaced wire harness behind the pedal and replaced the sensor under the pedal several times.
All brake lights come on, even the third light in the back window.

 

The only thing the CHMSL circuit has in common with the stop/turn signal circuit is the pedal position sensor and the BCM and the wire between them..

Either somebody mucked with the wires or we got another case of Space Aliens.

I tend to get suspicious when questions like "Did something happen just before this started? Somebody installing something electrical, somebody working under the hood, somebody replacing the radio etc?" get ignored.

 

Check the ground wire inside the access opening back by the tail light, check the tail light pigtail and bulb socket, does it appear burnt!
What bulbs are installed back there

 

My problem is that my brake lights pop on at any given moment and shuts down my cruise control when it's operating. Sometimes when I flash my brights off and on a few times. They go out. And other times, they go back out on their own, and then there are times they just stay on. I have had a new pigtail wire connector replaced and that seemed to help some. Have had the brake light switch replaced several times. Does anybody have any other viable ideas ??? It's been going on for a long time !!!

 

Threads merged. You should answer the questions asked by donbrew back in july.

 

Seems a problem in the wire harness, did you inspect the ground wires in the back? Just inside the access doors. Could be a faulty relay in the BCM , inspect for rodent damage and check the wires , for led resistors, also the bulb sockets themselves can melt and short out.

 

LEDs, trailer hitch wiring, backup camera? Any after market stuff?

The only way they could function without the brake pedal sensor is if a signal was applied between the pedal and the BCM. The pedal sensor is a variable resistor that uses 5 V ref and low ref for the end points; for ALL (the CHMSL is on a different trigger from the BCM) of the brake lights to operate there must be the correct signal on the yellow wire. I'm not sure if high or low is correct; low is anything below about 3.5 V high is 5 volts. My GUESS is a low signal sets the brake lights and somebody has tapped into one of the wires between the sensor and the BCM.

Anyway. the problem is most likely between the sensor and the BCM. A short to ground or a theft of voltage. Since low ref wire is brown, my guess is somebody assumed it to be ground and tapped it for a LED.