Hello,

I just bought a 4.7l WJ.

Going through the list, a lot of the sensors are shot, as expected. Pretty sure the IAC is on the fritz, too.

One thing I've never seen is an UP sensor switch irrationality, or something like that. What exactly is this?

When I shift it into reverse, it's fine, but when I go into drive, it shifts, engine revs a little (as is normal) then dies. I suspect this is a symptom of the TPS being bad on this vehicle. Correct?

Thank you for your help.

Regards,
Josh

 

What exactly engine and transmission do you have? And no, I would not think the TPS has anything to do with it, without a lot more info.

 

It's an N code 4.7l, non-HO.

Trim is Laredo.

I think the tranny is the 545RFE as that's standard in this application (with the V8) from '01 to '11.

Is there anything else?

I'm replacing the sensors due to age anyway. It kinda' acts like the MAP sensor, but had to order that in. I only go the Jeep last night so I'm still learning it.

It almost acts like the torque converter locks about 1/2 second after I shift it into a forward gear. Reverse is fine.

Codes are for the UP sensor pressure irrationality, and heater circuits on both the O2 sensors.

Regards,
Josh

 

What is a UP sensor? I've never heard of it. What's the "P" code

 

P0876

UD Pressure Switch Rationality

I aplogize; the U"P" was a typo.

Regards,
Josh

 

It's probably one of the pressure switches. There is a factory service bulletin for the 05 Grand Cherokee for this very problem. If your 04 was a late date production model, it could have one of these defective switches in it. There are 3 switches that monitor fluid pressure in various circuits in the transmission.

 

Dave, do you know where I might see that TSB? I'm searching but not seeing.

Thanks!

 

Got to cleaning underhood contacts since they were bad.

I pulled the TCM relay and the bloody Jeep doesn't stall out in any gear any longer -- I just have to shift it manually.

Any ideas on this?

Regards,
Josh

 

Go to automd.com which lists 76 TSBs for 2005 alone! They are not listed for specific reasons, just by number and category.

 

Awesome. Thank you, Dave!

Since pulling the TCM relay puts it into limp mode (albeit with no automatic shifting capability) would you suspect the TCM?

Regards,
Josh

 

"Limp Mode" sets the transmission in 2nd gear and won't let it shift to any other forward range. It's designed to just get you home and that's all. I had this happen when the governor pressure switch crapped out. This also set a trouble code.

 

Interesting. By forcing limp mode, it seems to be able to switch between gears 1 and 3. I don't have 2 and 4.

Regards,
Josh

 

Well, you have a different transmission that I do.