Jeep's been running great, except that the CEL light came on recently and the tranny sometimes downshifts from OD/4th gear above 45 mph. Was wondering if anyone else has had these issues and where I should start looking for solutions. Fluid and filter were changed 26,000 miles ago.
Cleaned the NSS 26,000 miles ago, too.

I disco'd the battery cables and touched them together, then cleaned every harness connection related to the tranny, to include the TCM and the ECU under the hood.

Here are the codes:

PO700

PO740

PO 743

 

Time to clean the contacts in the Neutral Safety Switch (NSS)

The Range Select Signal goes through the NSS and dirty contacts will cause shifting issues and result in P07XX codes being reported via a CEL.

 

i looked up the codes for
p0700 is transmission control system malfunction
http://engine-codes.com/p0700.html

p0740 is torque converter clutch malfunction
http://engine-codes.com/p0740.html

p0743 is torque converter clutch circuit electrical
http://engine-codes.com/p0743_jeep.html


hope this helps

 

FWIW,
the Torque Converter lock-up signal goes through the Brakelight Switch. a misadjusted switch will cause the torque converter to unlock at random times and this can lead to a misdiagnosis of bad solenoids or TCU.

An easy way to test it is to use your left foot to lift the brake pedal when at highway speed and see if the tranny stays in OD. Basically you wait till the tranny drops out of OD THEN lift the peddle while mainting speed with your right foot.

Make sense?

 

You guys rule.

Tries a few things and the CEL is still on.

While this might sound like a dumb question, I was wondering what a used TCU would go for at a yard. I'm considering buying one just to have as a spare.

Gonna drop the NSS tomorrow for a look-see. I cleaned it 26K miles ago but it wouldn't hurt to clean and inspect it, again.