97 blazer tranny intermittent problems

[bradleypa]

Hey all.

Some days you start the truck and all is well. then others you start and it's like you don't have 1st gear. If you pull the shifter to 1st it's fine and works so I know that it's electrical. It has been on the computer and it shows ( solenoid short torgue converter lock out.) something like that. But then when you turn off the vehicle and restart it everything runs great. I have replaced the ignition switch but could it have a play in this problem? the tranny did have work on it to fix a hard shift problem after driving on the freeway for a while. i believe they replaced the valve body. That work was done over 6 years ago.

The truck has 159 k
tranny is changed every year.

[old_master]

1997 S&T body GM vehicles use an ignition switch that is unique to that specific year, and it is known to have problems. Numerous, seemingly non related, electrical circuits throughout the vehicle will intermittently fail for no apparent reason. Another item that has been known to cause issues is the wire harness that connects all of the various electrical components inside the transmission: http://www.bulkpart.com/2/product/4L...d/74425NC.html I suppose a faulty ignition switch could be responsible for causing insulation on the wires in the harness to short to ground, but I have no proof of it, just a guess. Pinpointing the actual problem with the harness can be extremely time consuming and frustrating. On the vehicles that I suspected a faulty harness, DTC's indicated a short circuit in a shift solenoid circuit. I replaced the harness, and the problems went away That's not how I typically operate: I want to positively identify the cause, rather than throw parts at it. In this case, it's not cost effective to the customer to spend hours chasing a strongly suspected problem with a harness that is already known to have "issues".

I'm not saying this is the problem with yours, but it certainly could be.

The valve body has been a problem on certain, (not all) 4L60E transmissions when they get hot. The replacements, as you found out, take care of the problem.

[bradleypa]

This Wire harness that you speak of. Can I replace it, or do I need to get it in to a mechanic with a lift? I'm up for the task, but i'm not up for pulling the transmission out.

[old_master]

Not difficult at all, no contortionism involved It involves removing the transmission oil pan, unplug each component from the harness, remove the harness, install the new harness, oil pan, and refill with fluid. Takes maybe 2 hours, with an intermediate skill level.