Archived Truck in limp mode

[larryshew]

3 Miles from work tonight just coming off freeway and lost my speedometer and rpms to 0. ammeter reading low and transmission started slipping but got me to work anyway. Checked and wiggled under hood fuses and circuit breakers and in dash fuses and started up and now have tac. again? What gives ,and I am still at work ,swing ,40 miles to home, will it make it, or not?

 

[Extreme1]

Sounds like the PCM lost power. It needs current to lock the TC, drive the speedo and tach, and tell the voltmeter what to say. Start looking closely at the breakers and fuses under the hood, that sounds like the place to start. You could also check the connection to the PCM. It is on the passenger side on the firewall and has a 59 (or so) pin connector.



The rest of the truck will work but the voltage regulator is in the PCM so the truck will run on the batteries until the lights, in tank fuel pump and heater fan kill the batteries.

 

[larryshew]

Well I made it home and back to work the next day! It seems to me when I first got the truck a couple of months ago it did this when I switched the pac-brake on. I don't remember if I lost my amps,rpm or speedo I just remembering the transmission slipping and not going very fast, pulled over shut it off and started it up and everthing was fine. I also had a auto- loc installed then. I thought it was the pac-brake stuck on. But now auto-loc is gone and now I have a Smart Controller installed, but both where wired in to the PCM and I think the pac-brake and the Smart Controller switch was on when I let my foot off the gas,which would have activated the pac-brake and that is when I lost my gauges and transmission went to limp mode. Could there be a short that is overloading the PCM circuit breaker and does the breaker stay out until I take power away so it can reset?

 

[Extreme1]

I don't know. Check with DTT. I'm not familiar with any of that equipment, they should be able to help.