Got antifreeze in transmission, now stuck in 3rd gear (sometimes)
 

Calling all 4l60e experts!

So my blazer has been running great (1997 4x4) until one day the trans became stuck in 3rd gear and I noticed transmission fluid was gushing out of my coolant reservoir overflow. I replaced the radiator and flushed the trans about 5 times, and flushed the coolant system several times as well. After doing this the Blazer ran great for about a year. Now its doing it again, and I replace the fluid + filter, and its good for a few days, then its starts doing it again. Sometimes its stuck, but I turn the car off, and then on again, and then it works fine (weird?). Is this a PCM problem, shift solenoids, or do I just need a rebuilt trans?

Does the check engine light turn on with the bulb check?
Is the check engine light on while driving?
If so, what DTC's are in memory?

Only one way for trans fluid and coolant to mix... bad radiator. Sticking in 3rd gear could be a stuck solenoid inside the trans. If the solenoid has a problem, it should set a DTC in memory.

The radiator was replaced about a year ago because of the trans/coolant mixing, I flushed the trans 4-5 times since then with amsoil atf (great stuff), seemed to work great just after flushing/filter change. These are the codes that are currently in memory:

p0740 torque converter clutch circuit open
p0753 shift solenoid a electrical
p0758 shift solenoid b electrical
p0785 shift/timing solenoid malfunction
p1860 TCC PWM Solenoid circuit electrical

Is this a bad solenoid or what?

Did you read up on the codes in the Diagnostic Trouble Codes (DTCs) section?

Thanks, I didn't realize that was there. After reading all that, I'm still having problems diagnosing what is causing this, I dont think a single bad solenoid could cause all these codes, so I'm guessing the problem is electrical. Where can I find out which wires to test voltage for (especially from the ignition switch)?

Sounds like you got a bum replacment radiator.

Check all fuses and visually check the connector at the front right corner of the transmission. Large round grey connector, maybe 12 wires or so, might be loose.

Nope my coolant and transmission fluid have not been mixing since the replacement. UPDATE: I noticed that this problem coincided with the key getting stuck in the lock cylinder (unable to turn all the way to release key) so this was a sign that something was not right with the ignition switch, so I replaced it with an autozone duralast ignition switch. Started up and drove around with NO PROBLEMS, and NO CODES! Thanks guys!

Ignition switches, so many oddball problems, snap-on should make a kit with interchangeable heads to run diagnostics. Most likely would be too expensive for most mechanics.

looks like this problem is back again. I changed the ignition switch (again) with a brand new unit from ac delco, made no difference. Does anyone know which pins to check for power on the harness (the connector near the trans pan)?