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Ok, I’d first like to say this is my first time here, and glad to be here.
I have a 1997 Oldsmobile Bravada,AWD. It has 188k miles on it. It is throwing a p0785 code at cold start. I’ve replaced the downshift solenoids, checked connections when transmission pan was dropped, After a while of driving it and clearing the code several times, the problem goes away until after it sits over night. I live in California, no severe heat or cold. I’ve checked the transmission fluid, swapped ignition switch, verified voltage at fuse when CIL was on and off. Read at 12v before ignition switch was swapped, now reads at 14 after swapping. Verified battery and ground to battery. I’ve searched and searched but have found nothing but the ignition switch being the culprit. When p0785 activates, shifting is extremely rough. When code is gone, it shifts great, transmission fluid was a bit brown but didn’t smell burnt or any odd signs. Im at the point where Im now stuck at a crossroad. Any suggestions on what to check would be great!!! Thank you!
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It does sound like a electrical issue. does the instrument cluster stop working?
see if this helps.Unfortunately, the cluster doesn’t stop working. Kind of hoping it would for easier diagnosing! I’m glad to hear that someone else thinks it sounds electrical. I’m going crazy here!
With the key on, using a test light or voltmeter, check for battery voltage on the power side at fuse #20.
If there is no voltage there, the ignition switch is faulty.
I checked for voltage at fuse 20, and I am getting 14v out of the fuse, with CIL on and also voltage with the CIL off in the on position. To the above post, I’m going to assume it’s going to be between the fuse panel and the actual wiring to the transmission at this point. I honestly haven’t gotten that far yet to test everything underneath. I see it states to check the 1020 connection, which exactly is this?
Ok, so there are a couple of things to check now. First, check fuse #24 for battery voltage, key on. Next. check the transmission solenoid grounds. They are on a blk/wht and tan/wht ground wire connected on a bolt or stud at the rear of the left cylinder head. There may also be a blk/wht ground wire connected on a bolt or stud at the rear of the right cylinder head. Next, at the transmission where the wire harness connects, there is a pink wire (this is circuit 1020) that supplies voltage to the shift solenoids (key on). This is the other end of the wire that connects to the fuse previously tested. If the ground wires are ok and battery voltage is available on the pink wire at the transmission then either the VCM isn’t commanding the solenoids or there is an issue inside the trans. The VCM also relies on feedback from the engine coolant temperature sensor located on the thermostat housing, the throttle position sensor, and the vehicle speed sensor, so you may want to test those components if power and grounds are good.
Wow! Very informative, thank you all very much. I will give it some more testing either tonight or tomorrow morning and post feedback. Again, Thanks!!!!
You’re welcome. Also, keep in mind, that you should only test while the condition is occurring. If you test when it is operating properly you will probably not find the issue unless it is very obvious, such as a loose wire or insulation damage, etc.
Ok guys. So, I checked the 1020 circuit with a line tracer, I have no breaks cuts or anything of that sort on the pink wire from the fuse panel to the transmission harness. Here’s something I did notice though.
It seems this issue is occurring only when the car is completely cold. Only at startup. Kind of leading me to believe that either A it’s a sensor, or B it’s the computer itself like you guys stated above. Once the car gets to operating temperature, the problem goes away and stays away. I also noticed that my oil gauge is dropping during turns and decreasing speed. (I know Im good on the oil amount, as i check periodicaly, and checked once i noticed it was happening) I know that theres a good chance that its probably my oil pressure sensor, but is there any chance that these two things could be related? I’m going to start checking my sensors as stated above. I really appreciate all your time and knowledge.
I also noticed that my oil gauge is dropping during turns and decreasing speed. (I know Im good on the oil amount, as i check periodicaly, and checked once i noticed it was happening) I know that theres a good chance that its probably my oil pressure sensor, but is there any chance that these two things could be related?
Those issues probably aren’t related unless both are caused by a poor ground, but it’s probably the oil pressure sender for that one.
Ok, so after weeks upon weeks of not being able to fix that p078 issue, I finally got around to really spend some time with it. Unfortunately, I don’t know exactly what I did to fix the issue, but I thought I would share on what I did find.
I got constant and correct voltage at all circuits, fuse was ok, wiring was not showing any visible sign of shorts, melts, or breaks. I did however inspect the pinout that attaches to the top of the transmission. It was wet. Not wet with tranny fluid however, but a dirty water look. Believe it or not, this did occur first shortly after a carwash. I spent some time cleaning and drying the connectors, but with no luck on repair. I then realized that I did put on a new TPS earlier for other reasons non related to this, and decided to double check reference, I took it out and basically started from scratch on that to verify correct readings. I then once again dropped the pan, verified all connections, then noticed my 1-2 solenoid, it was pretty wobbly (I know, I should have paid more attention the first time!!!! Ugh!) So I replaced the solenoids since I had the pan opened once again. Side note, I got a hold of a bi-directional scanner and was able to command the 3-2 solenoid on and off, which then triggered the p078 CEL when it wasnt acting up. I sealed basically all of connectors with grease, and 3m tape. Well, after all of that, the code seemed to not come back. I thought I would at least put something here incase someone runs into the same issue. Now im running into a p0122 code, but thats a whole new topic! 🙂 LIke i said, im sorry for not posting the one true fix, but hopefully this somewhat helps someone in the near future. Thanks again for all of your help everyone!!
Thanks for keeping us updated. Yea, I’ve seen lots of issues when washing engines if that is indeed what you did. If not, perhaps the water in the connector caused the issue. No matter what, I appreciate you coming back to provide that information. It may just help someone else with a similar problem.
Thanks for using the ETCG forum. We’ll keep an eye out for your post on the P0122.
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