Monday, November 19, 2012

Blazer won't shift into 4WD

Trail Blazer Wont Shift Into Four Wheel Drive

Try shifting from a stop, shifting when in neutral.

When the 4x4 does not work it sets a code and it's stored in the TCCM (transfer case control module) you need a shop with a tech 2 scanner to retrieve this code.
If you do have the (auto4hi) button, then you can only see codes with a scanner. 
The other Blazer 4x4 system without the automatic t/case can be diagnosed without using a scanner.

Possibilities for the problem :----
If the lights flash when you try to engage auto 4hi or 4hi, but it won't complete the shift, then the problem is with the vacuum solenoid that engages the front diff.

The Vacuum  solenoid details :-----
Its  mounted to the firewall right above the distributor at the rear of the engine. 
To confirm the issue with soledoind,these  quick check will help.
You have to disconnect  both vacuum hoses from the solenoid, verify there is vacuum on one
of them (engine running) and then manually stick them together and see if the 4x4 completes it's shift. If so, you most likely need a new solenoid.

If that is checked ok,then 
Most likely problem is the encoder motor that's bolted on the T/CASE,,, 

Also one more thing,are the on dash 4wd lights coming on when you switch from 4wd to 2wd hi and low.
If no lights on the switch, and the 4x4 fuses are good then you need a TCCM and it has to be programmed.

When you try to switch on 4wd does it makes any clicking noise or no noise at all.
Is it trying to shift or no moment at all.

Suppose if its trying to shift this clears that  the module and the switch are fine, you either have a damaged trasfercase or a damaged encoder motor. 


Encoder motor is the electric motor that actually shifts the transfercase sometimes go bad, the best way to check for this would be to take the encoder motor off and shift he car from 2wd to 4wd hi and low and watch the motor turn, also when you take the motor off you can manually try to turn the transfer case selector shaft although its hard it can be turned using a wrench, if it turns ok then the encoder motor is damaged, if the encoder motor is also out of range the truck will do these things. 
After you take the encoder motor out place the transfercase in 4wd hi and also put the switch on 4wd hi and try installing the encoder motor so that all falls in place, if there was some kind of misalignment between these two then the car does this exact thing yours is doing.

These details will help.

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