I just noticed that when I put the truck into 4wd...both the 2hi and 4hi or 2hi n 4lo light stay on...seems like the front axle locks when I Jack it up I feel the axle is engaged...and u can hear the encoder motor working...no flashing lights...and it has a year old ac delco vacuum switch...any other ideas

 

Advise year of vehicle and whether 3 or 4-button control.

 

3 button controller...it's a 96

 

Please first check for codes as described here and report.

https://blazerforum.com/forum/tech-a...gnostics-7683/

"If the shift select buttons all blink one time and stop, and do not continue to blink, no fault codes are stored in the TCCM". Make sure the buttons blink one time and then stop if you report no codes stored.

 

No codes.

 

Do buttons blink one time and then stop?

 

I put the jumper in...turned the key...they lit up n just the 2hi stayed on...did I do it wrong?

 

Ignition off - jumper pin 13 - key on and watch. I'm guessing it is OK.

1. Check fuses. You can look at the following to help id all the fuses involved. ATC and Courtesy fuses

https://blazerforum.com/forum/2nd-ge...-blazer-89670/

2. Check for corrosion on the 12V terminals on the TCCM - this is common.

3. If OK, then I am guessing the TCCM is bad. No other reason for multiple status lights at the same time IMHO. See schematic in page 3 of the link above.

Hope this helps...

 

The thing is that the front axle locks along with the drive shaft..so the 4wd works but I have both lights on...weird...I'm going to take off the tccm harness n clean it...if the tccm was bad I wouldn't have 4wd correct? Would the 4wd indicator switch be bad located at the front axle?

 

I don't believe there is any indicator for the front axle being engaged on any of the systems. ONly way to check front axle being locked in is to jack up the right front wheel (only) and it should turn freely when not locked. When front axle is locked in you would then have to turn the front diff and driveshaft if it will turn at all. I suppose if you can't turn it at all then that would be an indication the transfer case is also locked in. Lights on the control buttons are controlled solely by the TCCM based on where it thinks the encoder motor on the transfer case is sitting by feedback from the position switch on the encoder motor. I don't think it is possible for TCCM to think it is in two at the same time (it would have a fit) - hence why I suspect bad TCCM. Good luck! And don't forget to check grounds for TCCM with an ohm meter. They can do weird things, and I believe the ground for the TCCM is under the vehicle exposed to the road. Good luck.