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I got a 2008 2.2L Cobalt automatic about a month ago. On Monday I had driven down a muddy dirt road. On Tuesday I washed the body and sprayed the undercarriage. On Wednesday I was driving to Atlanta which is 100 miles away and it was raining and about 10 miles from my destination I noticed that the RPMs were running 3500 at 55 mph which is normally 2500. It seems that it was no longer in overdrive. I noticed that the coolant temp was going up too so I turned the heat up and ran the fan.

I had to drive home at 45 to 50 mph on the highway as it wouldn't go into high gear.

On Thursday I took it to Autozone and had them run the codes. They got a P0700 Transmission Control System and P0977 Shift Solenoid B Circuit. I took it to AAMCO to check it out and they quoted $3000 for a rebuilt transmission or $981 for the shift solenoids to be replaced.

On Friday, I figured that the solenoids are activated by electrical signals and maybe the mud in the engine compartment had something to do with it. So I sprayed under the hood and cleaned the connectors. I had disconnected the battery first. I noticed something strange. The bottom ECM connector had oil on it where the connector plugs to the ECM. I don't know why. I tried to clean it. When I got it all back together, more problems. It displayed Engine Power Reduced. The throttle would not work. I tried to test drive it down the road but no power. It just idled. It would not go back up my driveway. On Saturday I worked on researching and tracing wires. I tried to figure out why the Throttle body sensor and the throttle body motor was not working. It had to be the ECM as the throttle pedal and Throttle motor goes to that. I sprayed some electronic cleaner on it and put it back together and it worked. The Engine Power Reduced display was not on and no CEL. The throttle now worked.

But when I took it for a test drive, it still would not shift to overdrive and the rpms would act like it was in neutral by going up and down and not affecting speed I'm not sure if that is a torque converter problem or transmission. One problem fixed but still the original problem.




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You might check and see if the wires are exposed. There should be black wire loom covering the bundle of wires in the harness. They may have rubbed through and are grounding. Connector could also be damage or wires pulled out of it. Those are the simple things to look at.

Testing the actual wiring is probably beyond what Aamco does. They would need to test further to see if the solenoids are actually being powered from the harness. Signal comes from tcm to transmission.

By chance are you having problems with the abs? That also seems to be an issues where the abs module will interact with the tcm when it’s shorted out or going bad.
 
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