Here is the problem it seems that the transmission has a hard time wanting to shift into overdrive. At first is was an once in a while thing, maybe every 4 or 5 months but now it happens a lot. If I use the tow button it will shift back into 3rd and everything seem fine. BUT I am also getting the fault code of 12, yes I know it means the battery has been disconnected, but the thing is the battery hasn't been disconnected in a year since I clean the terminals. Also getting an check engine light now and then but when I check for codes nothing but code 12 shows up. So I was wondering could all of this be caused by a faulty PCM? If not what else could be the problem. This has been a great truck since I got it.

 

Might be the O/D solenoid getting sticky, or a bad connection somewhere. O/D solenoid is a very simple circuit, Trans relay supplies 12 volts to the trans, PCM just grounds the circuit for TCC, and O/D solenoids. If TCC works fine, then it's likely just a bad connection, or bad solenoid.

 

Is your speedo working? Might be the OD solenoid in the trans. Pcm engages the OD solenoid at approximately 45 mph. If the speed sensor is failing the pcm doesn't know how fast it is going.

 

since it’s a battery code have you cleaned the post. Do you live in a rust state? If truck gots rust add grounding wires. Near PCM, check for damaged wires 20ga brown, 20ga orange/black tracer/ depends on motor which pin location is to test the wire. Problem to watch for is a single strand will give a continuity, but can’t handle a load (current), therefore a slugish shift or none. Brown wire is the overdrive grounding path to PCM

 

Year old thread, and the original poster hasn't been back......