Replaced the TPS, now shifting into 3rd, but won't shift into fourth. Tried the O/D dash button, light & no light but nothing.
Can I use a toggle switch to activate the OD at the trans?
What is the name of the part on the bottom of the trans with two wires yellow/green & blue or gray, my eyes arn't what they used to be, that activates the O/D.
Can I disconnect it & always have O/D?

 

PCM controls ground side of the circuit for O/D, and TCC, (along with the rest of the trans functions) thru the 8 pin connector on top of the valve body. (about halfway back, drivers side.) Are you getting any codes?

 

Is your speedo working?

 

Speedo is working, trans guy says no codes. That's why i started with the Throttle Position Censer & it's not adjustable.
How to test the O/D lock out switch, the light goes on & off. I'm stumped.CT

 

The switch just sends a signal to the PCM, that you don't want O/D, the PCM then turns the light on, acknowledging that you pressed the button. So, if the light goes on and off when you hit it, its working as advertised.

PCM will disable O/D for a couple reasons, trans temp not where it thinks it should be yet, trans temp too hot, (but, not hot enough to turn on the trans temp light yet......) no speed sensor reading to the PCM. (on your truck, PCM is on a parallel circuit, so, while the speedometer may be working, that doesn't necessarily imply the PCM knows how fast you are going.) The only condition that will actually set code (of these) is no speed sensor signal. Other problems would be a bad solenoid, but, the PCM would figure that one out in short order, and set a code. So, this is likely a temp problem. PCM thinks the trans isn't warm enough yet, or, it thinks it is TOO warm. Need to plug in a scanner, and see what data the PCM is getting when it *should* be shifting into O/D.

 

Thanks, got O/D.

 

What did you do? Or, did it just start working again?