2nd Gen Non-Engine/Transmission PCM reprogramming?

[WestTN]

I was doing an oil change today and decided to give a listen to the lift pump on my truck to see if it might be getting weak. As you know, the lift pump runs for a second or so when you turn the key on. I was not bumping the starter to get the longer pump cycle, just letting the chime ding one time and then turning the ignition off and back on. On the third cycle of key-on, I noticed a message appear in the odometer display. I missed what it said the first time, so I tried it again. Then I read "P Pcu" followed by "- - - - - -" and then "P done".



I've looked in the manual and it does not reference a PCU, only the PCM. I wonder if it is reprogramming the PCM from ROM?



I can't see that the truck runs any different from before doing this. Anybody got any ideas here?

 

[emjay]

You stumbled upon the secret code dump. If you cycle the key on and off 3 times, leaving it on on the third, any codes that are stored in the PCM and ECM are displayed on the odometer.

Neat, huh?

 

[HVAC]

Code Recall

That is a very cool feature!



I've used this trick when diagnosing a problem.



Once you have the code it's convenient to fire up your service manual on disc to look up the deffinition.

 

[WestTN]

PCM Prog...

Thanks for the answers, guys. The good news then is that there were no codes to read.