This 2008 Chevrolet Silverado came in with the complaint that the cruise control would not work. Since I have a Tech 2 scan tool I decided to look for codes first. There was a PCM code P0573 stored for the “Brake Switch Circuit 1 High Voltage”. Simply put the computers think that the brake lights are on and the cruise control is disengaged.
The test is to look for power on the light blue/white wire at the stoplight switch. The key must be on and you will want to check for power on that wire with the brake pedal released and also gently pushed.
What was happening on this one was that the cruise would engage and later it would turn off because of a very sensitive switch and rough roads. An easy test is to drive the vehicle until the cruise turns off. Note the roughness of the road. Driving under the same conditions and of course with no other traffic around, place your left foot under the brake pedal and gently lift up. Try the cruise again. If it continues to work depress the brake pedal to disengage the cruise control. It should be noted that a problem with a towed vehicle wiring can result in a similar condition with the cruise control.
I knew I needed to get to the stoplight switch and removing the lower duct work would make that easier.
There is a push pin retainer that holds the outer end in place. Once it is removed the duct can be slid out of the vehicle.
The stoplight switch is shown slightly above center in the following picture.
There is a bolt with a 10 mm head that needs to be backed off or removed so that the reatining clip can be removed.
The latch that holds the harness to the switch has to be depressed before the harness connector can be removed.
A few closer looks at the switch retainer with bolt.
The switch strangely enough looks quite a bit like the old Ford stoplight switches.
This vehicle had adjustable foot pedals and the view would be slightly different if the pedals were of the fixed type.
Although this is termed as a BPP (Brake Pedal Position) switch within GM Service Information no setup or programming is needed when replacing this switch.
If the code had been P0572, testing would have started at the Misc IGN fuse in the underhood fuse box. It would be in position #43 with a gas engine and position #40 with a diesel engine. This fuse sends power to the stoplight switch on the pink wire.