So new to the forum! I have a 06 jeep wrangler Tj 4.0 with the auto. Been fixing it up and it was idling outside my shop and randomly died, no check engine light but doing the key on off if showed p0688. Currently it no crank no starts and I don’t here the fuel pump or any relays clicking even after swapping the ADS with a few I know are good. No blown fuses and I got it to start twice moveing the pcm harness around but now it won’t crank at all and I’ve inspected the main harness and the room and can find anything the is alarming. Am I looking at a pcm? Hard to believe it would just go out after driving it for weeks with no issues
P0688 issues
- Thread starter PremierTJ
- Start date
@PremierTJ it sounds like the pcm has failed you. How is your shifting from 1st to 2nd in the morning?
When cold the 1-2 is a little stiff, but once warm the 2-1 down shift slightly grinds then falls into gear when almost at a complete stop
The little stiff shift is the transmission side of the pcm that is failing. Our computer will resolve that and the P0688 code!
How long does those normally take to ship out? I’ll order one today if I need it
There is no shipping on Monday because of the MLK holiday. So it would ship on Tuesday and I can get it there as quickly as Wednesday.
Guess I’ll be ordering one today, is there any test I can do on the pcm to confirm it’s dead or is just a shot in the dark
Yes, there is. You can send the computer into us and we can run it in one of our jeepss. We usually get them tested the same day they come in.
Thanks,
Mark
Thanks,
Mark
Hooked the new one in from Wranglerfix and she fired right up! No hidden codes and idles smoother then before I’ll post later after a few drives on the transmission issues I had before mark is THE MAN
When for about a 75 mile drive and up shifts are nice and smooth but I still have a grinding noise when it shifts from 2-1 coming to a stop so must be mechanical or something else
"Grinding noise" is pretty vague. Maybe @PremierTJ can post a video to YouTube and share the link here?
I get some vibrations from about 25 mph to 30 that smooth out with more throttle...I think I have an out of balance tire...but when you hit 25 a lot of loose stuff rattles and hums when you hit that perfect spot.
So it could be the transmission...or something completely different.
I chased a front end noise for months that ended up being my rear driveshaft.
And as always... wiring and grounds...seems like the newer the TJs got the quality of the wiring harnesses plummeted. Could be frayed wires going to the transmission plug.
Everything would be wild speculation at this point.
Best bet is positively identity the source of the noise...is it truly coming from the transmission?
-Mac
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