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Questions and Answers

Jeep Cherokee Transmission And TPS

Q. Dear Vince, I have a 1992 Jeep Cherokee with the 4 liter engine and the 2WD AW4 transmission. I bought it used. After driving it for a couple months, the transmission began to shift only after getting the engine up to 4,500 RPM. I could get it from first to second, and from second to third, but getting it to fourth was impossible.

Jeep Cherokee Transmission And TPS

I took it to a local transmission shop and they checked it out. They called to say they needed to open it up. They arranged for us to get a rental car, which they would reimburse after the car was done. They called two days later and wanted $1,900.00 to rebuild the transmission. The mechanic said he checked for recalls and service bulletins and found none.

I decided not to have it repaired, and brought it home, after paying $400.00 plus $300.00 in car rentals. I parked the Jeep in the driveway. After a while, I got curious and started doing research on the web.

I discovered a service bulletin on my Jeep on "Alldata.com", which indicated "A/T - Throttle Position Sensor". I don't subscribe to the site, so I could only see this header. I then did a search on Throttle Position Sensor and found a number of sites that described numerous transmission problems attributed to this sensor.

I took the Jeep to a Chrysler dealer near me, and purchased the part for $69.00. I installed it myself, and the Jeep shifts beautifully, better than when I bought it. I called the shop back, because they told me they took photos of the transmission and I was anxious to see them, and to show them to another mechanic to see if they had been honest.

hen I called the shop, the guy that answered told me he had been building transmissions for 28 years, and that the Throttle Position Sensor had nothing to do with the transmission. I explained what I found, and that replacing the sensor had fixed the problem. He then said that the TPS sends "line pressure" to the transmission control module.

He told me that replacing it would make the car SEEM to be better, but that it wasn't really fixed. I then told him that the problem had not gotten worse before I brought it in, even though it had been shifting badly for over a month. He then said that driving with a bad TPS could CAUSE damage to the transmission. I believe that everything he told me was basically bunk.

From what I've read, the TPS sends VOLTAGE to the TCM, not "line pressure", and that if the transmission was damaged to the point of needing an overhaul, replacing the TPS would not make it run perfectly. Am I just dumb, or am I being handed a bill of goods. I would dearly love to get my money back for this non-repair.

Thanks,
Kyle

A. The TSB you are refering to is number ATRATB324A, dated 1/1/1996 witrh the subject "A/T - AW4 Throttle Position Sensor (TP)".

The Transmission Control Unit does, indeed, use an input, among others, from the TPS to determine shift times. So if there is a problem with the TPS, it will effect transmission shifting. In fact, it is not all that uncommon to see a TPS cause a transmission problem.

Anyhow, I think there's a valid complaint here given the circumstances. I would recommend that you take this up with their local Better Business Bureau. If the transmission works fine then I would only recommend that a routine flush be done to it and perhaps treat it to a new filter.

And I think the 28 year mechanic study up on the new transmission control systems.

Additional Information provided courtesy of ALLDATA

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