Intermittent problem

[joedown]

I'm having an issue that comes and goes. Cannot go in reverse. Forward gears work but high RPMs before shifting like it's in limp mode. No trouble codes are thrown. When the problem goes away everything is normal. Lets say there is nothing wrong with the transmission. Where would I start to look for this issue? Could this be an ECM issue?

[joedown]

This is getting frustrating! Got home last night and started it up. Put it in reverse and backed out of the driveway no problem. Took it for a drive and everythings working normally. Not sure how to troubleshoot an issue like this that comes and goes. Does this sound like an electrical or mechanical issue?

[madpogue]

Next time it doesn't go in reverse, if you're lucky enough to have an assistant with you, (or if it's dark enough), have your assistant hop out and see (or look in the mirror to see) if the reverse lights are on. If they're not, it may be a problem with the range selector/sensor, aka MLPS, aka neutral safety switch. It may be faulty or out of adjustment. That or slop in the steering column. In either case, the PCM doesn't "know" that the tranny is in reverse.

How did you determine there are no codes? What scanner did you use?

[joedown]

Originally Posted by madpogue

Next time it doesn't go in reverse, if you're lucky enough to have an assistant with you, (or if it's dark enough), have your assistant hop out and see (or look in the mirror to see) if the reverse lights are on. If they're not, it may be a problem with the range selector/sensor, aka MLPS, aka neutral safety switch. It may be faulty or out of adjustment. That or slop in the steering column. In either case, the PCM doesn't "know" that the tranny is in reverse.

How did you determine there are no codes? What scanner did you use?

I checked that my reverse lights come on when I put it in Reverse. I tried rocking the shifter but it is solid. I used Auto Enginunity. Actually there was one code stored but it was for disconnecting the batteries awhile back.

[madpogue]

I have AE, but don't have access to an automatic truck to try it in. I _think_ you can get it to read what gear the tranny is in. Again, the trick will be having the AE program running and checking the next time it happens. IIRC, just browsing the EVTM one day, there are separate contacts and terminals on the trans switch for telling the PCM what gear it's in, separate from the reverse lights and neutral safety. So it may still be that the PCM is not aware it's in reverse.

[BigFuel]