scan tool shows brake on always

95 Jimmy 4.3 W with vehicle specific diagnostic link under dash. Scan tool shows brake on all the time. I replaced the brake light switch but problem remains. TCC and cruise will not work because computer thinks brake is depressed. Brake lights work correctly.

I have a volt / ohm meter but don't have a wiring diagram or troubleshooting guide to know what readings I need and where.

Any help will be appreciated,

Some have 2 brakelight switches, one for the brakelight and one for the cruise control.

If yours has 3 or 4 wires, 1 pair make a normally open circuit for the brake lights and the other pair make a normally closed circuit for the cruise control.

Thanks for your input.

There is only 1 switch on the brake pedal.

It has 4 wires - White - Orange - Purple - Brown.

I dropped it today and checked it with a volt meter.

Orange is always hot - key on or off.
With key on and brake off orange - purple and brown are hot
With key on and brake on orange - white and brown are hot

It appears to be working correctly but the scan tool still shows "brake on" no matter what.

If time allows tomorrow I will see if I can get to the computer under the dash or pass kick panel. I am not one of the lucky ones with the computer in the engine compartment. I will try to find the purple and white at the computer and see if the readings match the brake switch.

Any other suggestions or thoughts will be appreciated.

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I have found what I believe to be the purple line from the brake switch to the computer - attached is a picture.

I believe this wire should read 12+volts but it does not. I think that is why the scan tool reads "Brake depressed - Yes". I believe the computer needs to see 12+volts from this wire to know the brake is NOT depressed.

The easy fix for my problem may be to run a new purple from the brake switch to this pin on the computer. Of course if I am wrong and feed 12 volts to the wrong place on the computer I could toast it.

Anyone out there that can confirm or deny if this wire should read 12 volts - 95 GMC Jimmy 4.3 Automatic?

SORRY - I see the picture is not included - I pasted the URL as requested so not sure what I did wrong.

I think you have a ground problem, belive one of the wires should be grounded. But I can't find my Haynes to check the diagram to see wich one :frown: I'll try to find it and if I do I post again.

/Freddy

Thanks for your input.

There is only 1 switch on the brake pedal.

It has 4 wires - White - Orange - Purple - Brown.

I dropped it today and checked it with a volt meter.

Orange is always hot - key on or off.
With key on and brake off orange - purple and brown are hot
With key on and brake on orange - white and brown are hot

It appears to be working correctly but the scan tool still shows "brake on" no matter what.

If time allows tomorrow I will see if I can get to the computer under the dash or pass kick panel. I am not one of the lucky ones with the computer in the engine compartment. I will try to find the purple and white at the computer and see if the readings match the brake switch.

Any other suggestions or thoughts will be appreciated.

Thanks for your reply - I have a haynes - it shows the cruise circuit but not the pinouts for the PCM. It looks to me like the brake switch sends 12 volts to the cruise module and PCM via the purple wire when the brake is not depressed. I DO get 12 volts at the purple at the brake switch and I have found a purple at the PCM. I DO NOT get 12 volts at the purple at the PCM. The haynes shows it as circuit 420 for the automatic.

I am trying to confirm if the purple I am testing at the PCM is the correct wire and if it should read 12 volts at the PCM. I tried to post o picture of the PCM and wire but it didn't work. I might have a better manual at the other house in TN, we are in the middle of moving. Problem is I need to drive this Jimmy from NJ to TN - 700 miles. Right now the cruise and more important the TCC will not work as the computer thinks the brake is on. I hate to drive 700 miles with the TCC unlocked - I can handle the extra gas but worry about the extra heat to the trans.

I don't know if this applies, I'm looking at '97 wiring from the manual.
The purple wire from the brake light switch goes to the Cruise Control Module (CCM) through input "D". The white wire goes to the CCM through input "G" (I don't know it these are stamped or marked on the CCM).
The PCM gets cruise control info from the CCM output "J", a light blue wire w/black stripe.
The Cruise Control Module is shown to be under the hood, behind the Power Brake Booster.

Thanks for the reply - I also have a 97 LT Blazer but it is in TN so I could not use if to compare. I just got back from a ride and all is working OK now. I hope it is because I unplugged and cleaned the terminals at the PCM while I had it out last night. If that is the case I got lucky and it was just from 12 year old connections / age. If it comes back it means I have an intermittant break somewhere. I hope not because they are usually a nightmare to locate. Now that all is working I rechecked the purple at the PCM and it still does not show 12 volts so , I was on the wrong track there.
Thanks to all for the help - Don