Engine/Transmission (1998.5 - 2002) APPS/TPS Sensor Problems

[PCrable]

My APPS Sensor (formerly know as the TPS to the undervalved) has been acting up lately. I'll be driving along just fine and the engine will drop to idle and the "Check Engine" light will come on. If I let off the go pedal and push down again, the truck will run normally again (except for the good old check engine light). The fault code is P0121 - "TPS A Circuit Range/Perf"



This had been happening fairly infrequently, but seems to be getting more frequent... 3 times on the way home yesterday.



I now hold in my hand the Bell Crank assmebly with the APPS Sensor attached to it. According to the service manual...



"The APPS is serviced (replaced) as one assembly including the lever, brackets and sensor. The APPS is calibrated to its mounting bracket. The APPS assembly is located at the left-front of engine belowplastic cable/lever/linkage cover (Fig. 20)



CAUTION: Do not attempt to remove sensor from its mounting bracket as electronic calibration will be destroyed (sensor-to-bracket mounting screws are permanentyl attached).



A new APPS Sensor replaces the whole bell crank assembly/mounting bracket and lever. This assembly for a 98. 5 24 valve automatic costs about $410 from your local stealer.



The parts guy from AutoZone shows a replacement Wells TPS (Part # TPS332) for $127. I would assume that is just the electronic portion of the APPS assembly I'm holding and you would need to remove the old sensor and re-mount the new one... potentially messing up the electronic calibration.



The electronic portion of the sensor is labeled ...



56028184

7323 RE 0. 617 VDC

USA



It doesn't appear that if you took the sensor off that there would be any way to disassemble and clean it... it's a sealed little electronic box.



Thoughts anyone ? How sensative is this electronic calibration if I were to ignore the warning and try to replace or repair just the electronic portion of the sensor ?

 

[PCrable]

Man... no replies at all...



I ended up getting real tired of the engine dropping to idle saveral times on each outing and decided to go buy a new one .



I managed to get one of the local stealers to give me the APPS unit at wholesale cost of $326 instead of the list price of $409. The thing tha really got me was I could see on the screen while the parts guy was getting it that their cost for the APPS is $245 .



Oh well... Just in case it will help anyone, the part number for an APPS/TPS sensor on a 98. 5 24 valve with an automatic transmission is 53031575AF.



Anyone want to experiment with the old one to see if you can replace the pot and figure out how to calibrate it ?



--Phil

 

[Sean Flanagan]

When mine crapped, I ended up replacing the whole thing. But the dealer eneded doing it under warranty so it didn't bug me too much. I belive the APPS is just a little Pot, just like the ones on gas engines. At least, it looks the same. You could try disconnecting it and measuring the resistance with a meter as you move the throttle.



If it is a pot, all you have to do is adjust the new one so that it has the same reading at zero throttle (idle). I had to do this with my wife's Grand Cherokee.



I also remember hearing that the TPS was self calibrating. After you switch on the key, slowly press the throttle all the way to full then slowly back down again. I havn't tried it though.



Good Luck

 

[Justbeamn]

Sean, I reset my APPS by unhooking the batteries for 30 minutes, then turn the key to the on position, depress the go pedal to the floor and raise slowly.



I was having problems with the TC locking and unlocking at 43 mph. This did the trick.