Hey guys, new to the forum. I couldn't find anything too helpful on other threads about this.
I have a '99 Cherokee with the AW4 trans. For some reason, it won't shift into 2nd gear. When its in 1•2, it'll rap out at 4k-ish RPMs instead of shifting into 2nd. This is usually where I let off the throttle, because I'm scared to ruin other things. When just in regular drive, it'll do the same thing, rap out at 4k, and when I let off a touch, the RPMs drop to roughly 250 and then shoot back up to 1200 once it finds 3rd gear. Shifts into 4th (or OD, depending who you ask) just fine. It is throwing a code, P0756, Shift Solenoid B Performance/Stuck Off. Between yesterday and today, I replaced Solenoid A & B, but to no avail. Trans still will not shift into 2nd. Any ideas what it could be? tia.

 

I know on the pre-96 it could be the Transmission Control Unit (TCU) or the fuse to that. Not sure about 99's. Try searching around for some answers about that and see where it leads. Let us know what you find or if you can't find anything and we'll try to help you.

 

http://cruiser54.com/?p=58

 

I agree, it's time to check the wiring and connectors. The 99 trans computer will be on the drivers side. There are a pair of connectors up against the firewall (follow the wiring up from the trans). You can check and measure the solenoid resistance from both the computer and at the connector. Also test that the TPS sensor is not bad and the throttle-body cable to the trans is adjusted properly. I'm going to assume you have the right amount of fluid since you just dropped the pan to do the solenoids. Take a quick look at the lines from the trans to the radiator and make sure they're not pinched.

If everything else checks out, the computer could be suspect but it's rare that's the problem. Before dumping money into replacing it, see if you can backprobe the connector while driving or just the rear jacked up. You'd be looking to verify whether the computer is sending power to the solenoid.

 

Thank you all, I'll go test it now. Also, don't know if it's related or not, but since the trans started acting up, it also has had a rough/high idle. It sits around 1300 before aggressively dropping to 700 and flying back up again.

 

Haven't been able to find the trans computer.. however, the engine code for the trans cleared up.. Now its shooting three codes, P0121, P0122, and P0123, all having to do with the throttle body sensor, which makes sense for the rough idle. Now I'm more confused than I was, since the code cleared but it still won't shift.

 

If the TPS sensor is bad, it might be telling the trans computer that you've got it floored, causing it to hold in gear much longer. If you have a meter, the TPS is fairly easy to test.

 

Yup, sure enough, the TPS needed replaced, and after replacing it, everything was fixed. Appreciate the help from everyone!

 

Nice easy fix. I always forget y'all witb newer Jeeps have codes to help y'all out.