Still having issues trying to figure out my P0783 (no rpms drop in gears 3-4) and mil 45 code. Ive replaced all the solenoids in the transmission, 3-4 accumulator spring, output speed sensor and the TCC boost valve retainer. I was talking to a guy and he thinks its an electrical issue since mil code 45 says open or short in the solenoid circuit and the last two times o dropped the pan it was completely clean and the magnet barely had anything on it. He was saying I should check my transmission grounds but me not being a mechanic I have no idea where those are and cant find anything online. Anybody know where they are or if thats anything I should check?

 

TCC and O/D solenoids don't ground thru the trans. Power is supplied from the transmission relay in the PDC (black box behind the battery), and PCM controls ground side of the circuit. So, one of three things is happening here, either you aren't getting 12 volts TO the transmission, or, there is a break in the wires between the engine and trans, or, the PCM has an issue grounding those circuits.

Start with the easy stuff. ARE you getting 12 volts to the trans?

 

I did check one wire going to the pcm with my dad and it was 12 volts. I cant remember what wire it was exactly now I would have to check. I don't know if this would have anything to do with it but I just happened to be looking at my battery cables and I noticed that my negative cable and the ground coming off that negative cable that goes to my frame both have burns in them through the rubber coating and looks like it burnt kinda deep into the cable.

 

May or may not be related, but, probably should be addressed.

You wanna check for 12 volts AT the transmission. (I know, pain in the keester, especially if you have 4 wheel drive.)

 

So unhook that connector on top of the tranny pan and check there?

 

Yep, that would be the one. I *think* you will have to have the engine running.... either that, or someone sitting in the truck, cycling the key for you, as I think the trans only gets power for a few seconds unless the PCM sees the engine turning as well. (a lot like the fuel pump.)

 

Do you by chance know what wire to check or can I just check any one?

 

Red wire. Orange is from the PCM, and should be 5 volts.