95 Suburban 4L60E Trans Fail-Safe mode

My 95 Suburban has a GM-rebuilt 4L60E tranny that has been acting up. I think it has less than 20K miles on it, but it is now out of warranty. I drive this car only occasionally (gas prices waaah). I was experiencing harsh shifts from 1st to 2nd. Now it slips bad at take off from still, appearing to start in 2nd or 3rd. It pulls better at start if I select D2, then upshift to D3.

The fluid is full on the stick and not burned, although from the time of re-build the fluid is the slightest color of pink I have ever seen.

After reading many posts regarding 4L60Es and Fail-Safe mode in AF, and based on prior experiences, I think that the tranny is going into Fail-Safe mode. I dealt with Fail-Safe mode on a prior occasion, resulting in replacement of ignition switch.

I read the codes - 32, 42, 66, and 73. Then cleared out old codes and test drove. Got one good take off from stand still after clearing codes, then repeated slipping at subsequent take-offs. Didn't test drive far enough to see about OD engaging.

I re-checked the codes. I got a repeat of the two trans-related codes - 66 and 73 (and no others).

My Haynes manual (best manual I have but not much to work with) states that 66 code is 'ECM detects open or short circuit in 3-2 solenoid circuit', 73 code is 'ECM detects a fault in the pressure control solenoid circuit'.

I'd appreciate any advice or suggestions on how to fix this tranny and get it out of Fail-Safe mode.

Thanks in advance!
JP :grinyes:

The safest way but the most time consuming is to ohm the wires from the pcm to the transmission plug on the circuits detected by the codes. I fthe wires are ok then check the harness inside the trans, I like to replace all the solenoids, sensor and harness when I have to go inside the pan, but the pressure controll solenoid is expensive. My best guess is a faulty harness inside transmission.

HUNTERPAUL - Happy Sunday

I have a long story to tell that relates to how I fixed my tranny problem - but the short version is that I fixed my problem.

I was in the process of following your advice, setting up to ohm out the appropriate circuits from the ECM to the tranny, when I discovered that the top side plug to my transmission was not pushed in to the point of 'clicking in'.

After cleaning the plug with WD40, wiping dry with a shop rag, then pushing the connector back in to the point of getting a 'click' - my suburban now shifts right and is not throwing error codes - for the first time in a long time.

No more slam shift from 1 to 2, I have quick (relative speaking - it is a suburban after all) starts with no slip from take-off, I get OD, no more Fail-Safe mode, and no error codes after multiple re-checks.

After taking a close look at the tranny electrical connections, I started to notice a lot of sloppy work from the Chevy shop that did my tranny swap. Wire carriers were disconnected and/or screws missing, vent tubes left with no rubber tubes connected. It looks like a simple conclusion that the electrical plug was not pushed in far enough to make a solid connection. Evidenced by some darkness (arcing) on two of the connector plug female pins. No thanks to Mr Goodwrench. :rofl:

HUNTERPAUL - Thanks for your speedy reply - you put me on the right track! :rofl:

After taking a close look at the tranny electrical connections, I started to notice a lot of sloppy work from the Chevy shop that did my tranny swap. Wire carriers were disconnected and/or screws missing, vent tubes left with no rubber tubes connected. It looks like a simple conclusion that the electrical plug was not pushed in far enough to make a solid connection. Evidenced by some darkness (arcing) on two of the connector plug female pins. No thanks to Mr BADwrench. :rofl:

This is a very good post...thanks for the repair info!