hey guys bad things going on with tranny. I have a 1991 suburban 2500 6.2 diesel automatic. This Has only happened 3 times in the last month. I will start driving and it wont shift to 4th gear,I will stop and put it in park try shifting all gears everything seems good. start driving and still wont go into overdrive. So I stop and turn the truck off, start and go and it shifts into overdrive no problem. Everytime I will turn it off and it works after that. I am not sure what tranny is in it either.

Everytime I will turn it off and it works after that. I am not sure what tranny is in it either.
That in itself is a good indicator its an electric issue.

Physically you cannot shift into overdrive?

Electronically the computer is not letting it go into overdrive? The computer will not let the transmission into OD lock up for various reasons.

When I mean defective it can be the circuits going to and from those sensors.
Throttle position Sensor out of adjustment. TPS

Transmission range pressure switch defective. TRPS

Transmission input speed sensor defective.TISS

Vehicle Speed sensor defective. VSS

Transmission output speed sensor defective. TOSS

Transmission fluid temperature sensor defective. TFT

Torque converter clutch solenoid defective. TCC


Pull codes before you do anything.

You have a throttle position sensor on the injection pump. At idle the voltage coming from the middle pin .47 to .5. Check it.
Inspect the passthrough connector for leaks ie oil. Bent and or pushed in pins. Male or female.
Find the sticky on resistance checks for the 1-2 and the 2-3 shifting solenoid. Follow the post below.
http://www.dieselplace.com/forum/showthread.php?t=327063

There is a TCC solenoid that operates a valve. The bore and valve will wear. the signal is supposed to be sent to the control valve within the pump.
You can opt to replace the TCC solenoid and hope for the best. Or.
You can take the transmission into a shop and get the valve and bore resleeved.

its your tps....... mine did the same thing when i had a 6.5.......

thanks guys I will try that.

you can test it first........ go over to sixfiveturbodiesel.com and do a search for tps........ or go over there and look up my name b/c i had a huge write up on it...... same name as here....... :cool:

hey guys tried the tps not it going to take in to the tranny shop

could be a shift siliniod too....