Hey all,

I had a small thread in the LSx swap section, but thought i'd post here for the transmission gurus.

I was driving the car about a month or two ago, and the CEL came on. When I got home, I pulled the code, and got P0785 3-2 Downshift Solenoid. Having read that the majority of people who experience this, are experiencing a solenoid failure, I decided to pull the pan and replace the 3-2 solenoid. While I had the pan off, I chose to replace the filter, the 3-2 solenoid, and the A/B solenoids as well. Buttoned everything back up, refilled with new tranny fluid, and started the car...code was still there

Figured it was likely a wiring issue going to the transmission, or a bad PCM. Luckily had an extra PCM from the same year LS1 sitting at home, put it in, purchased a VATs Bypass module (the one i tried to build didn't work...my error I guarantee). And the extra computer starts the car just fine. I do get lots and lots of check engine codes related to the EVAP system, along with a cylinder misfire, and codes about no rear O2 sensors. But in addition I received codes:

P0753

and

P0758

I was happy that P0785 was no longer triggering, leading me to think that the PCM is what's defective. The car runs a bit rough, and surges at idle some (much more than I ever experienced with the old PCM) so now I'm wondering if this is normal or should I totally replace both PCM units with a new unit and have that unit tuned to remove the trouble codes...or, try having this PCM tuned and see if it's functional or not.

I'm also really curious is the P0753 and P0758 codes are related to all the other trouble codes I was getting, and if the transmission is in "limp" mode or something similar?

I did swap back to the original computer again, just to see if I was still getting the same message...and I had an IMMEDIATE P0785 code...further guiding me in thoughts that the original PCM is indeed defective.

 

Hey guys - just wanted to post an update (not that anyone is reading, but maybe this will help someone if they find they're having the same problem as me).

I found this test procedure (via internet search i think, was either linked on this website or through ls1tech) http://www.trutechtrans.com/Topic-1-00-01.html

I followed the procedure and confirmed.

I have 12 volts from the wiring harness to the transmission

I have 22 Ohms of resistance on the 1-2 and 2-3 shift solenoids (sadly I didn't check the 3-2 solenoid, but can at a later date I guess)

I'm showing infinite resistance between all harness wiring and ground, and between internal transmission wiring and ground.

I cycled the solenoids several times via 12v ignition source to ensure they're all operating, and all each solenoids 1-2 , 2-3, and 3-2 are all operating normally.

Before any testing, the car was incredibly sluggish when putting it into gear, and trying to move forward. Reverse seemed to operate normally, but forward gears required lots of gas. From a troubleshooting guide, this was a fault with the 1-2 or 2-3 solenoids not engaging, putting the transmission into 4th gear and causing the "no-moving" situation. The best comparison would be attempting to drive the car forward with your foot on the brakes, or having the emergency brake engaged.

After all the testing, I re-swapped to my backup PCM and got the car started...backed off the ramps, and did a few laps up and down the street. The car was not sluggish off the line the way it was previously, so that's a good sign, but we'll see if it lasts long term.

The only thing I did find wrong w/ the car about a week ago, was I was low on transmission fluid, so I topped that off. At this point, I'm happy that the car will ACT normally, even if it's just for a short period of time. And that the harness, and solenoids are operating normally for testing purposes. I'm still leaning towards a bad ECM, but I imagine we'll find out soon enough.

 

Alright - two LONG test drives in and the car is behaving properly.

When I refilled the transmission after replacing the solenoids I got multiple error messages, and although I shifted the transmission, waited, filled, shifted, waited, filled, it I'm feeling that my incorrect fluid level was causing at least part of my problem. The only thing odd is that it doesn't explain why I still received trouble codes after adding additional transmission fluid, and why the transmission was incredibly shaky despite the new fluid. End result, I'm feeling that it was a combination of low fluid, the bad PCM, and for some reason my solenoids not activating after adding the fluid. Seems after I got everything moving in the valve body, all is right with the world...now to get this old PCM setup to ditch the other trouble codes, and I'll ride off into the sunset.