Hi Scotty, great videos! I have learned a lot! 2004 Jeep Grand Cherokee, 88k miles. Tried to…


Hi Scotty, great videos! I have learned a lot! 2004 Jeep Grand Cherokee, 88k miles.

Tried to respond to a search for "Throttle Position Sensor". Signed up to reply on a related question. Didn't work for typing. So I post here. Short synopsis of a years worth of monitoring, research and stuff I did, instead of randomly throwing parts at the car.

In short, MIL light goes on, I fix something, MIL light off, then it comes back on. Some or all the TPS codes show up (out of range, faulty, etc.). MIL light goes out. Codes either reset or sitting in "history". Codes and MIL - on/off at random intervals.

I first tested the wiring. Symptoms made sense to me (I'm an electrical engineer). Volt meter and 12V light shows things are all working fine. Bent and twisted wires looking for a wire break (none found). TPS appears to be working with voltmeter testing. Cleaned and dielectric grease on the TPS connector. No problems there.

New OEM gas cap. MIL went out for many, many miles, and came back on, same TPS codes. MIL light decides to be an intermittent problem.

Checked for vacuum leaks, running engine and propane torch (gas only, no fire). No idle change/revving, seems ok.

More miles, more/same TPS codes, and MIL light is going on/off, randomly.

Another symptom also. A "random" symptom that led me even closer to the TPS. This was "idle hunt" when engine was warm, and came to a stop. Car almost died out at the light (< 500 rpm). Shift to neutral, idle increases slightly. Seemed to be worse on really cold or high humidity days as well. And of course MIL goes back off, and car runs ok and I'm also noting this random "idle hunt" symptom.

Zeroing in on a bad TPS. Studied my factory manual, and pulled out the whole throttle body. Cleaned the whole thing. Put it back in, Cleaned and dielectric grease for all connectors. Codes and MIL light all reset, and car computer relearned. Ran great, MIL off, no codes. Thought that fixed it.

More miles, and the MIL came on again, same TPS codes. Went to auto parts store and replaced TPS sensor. MIL light off (immediately, no relearn). Car ran great again. Also noted a bit better response for acceleration from a stop.

Again, many miles, and MIL light went on again with TPS codes. I hung on to the old OEM TPS, and decided to crack the thing apart. I immediately noted that the guts of the TPS sensor is a Hall Effect sensor. Everything I've researched says the TPS sensor is a potentiometer (same idea as an old school volume control knob on a radio). Factory manual says nothing about this.

You always advocate OEM parts over auto parts store replacements (good idea of course). Car is running good right now, and MIL light is off (for today, anyway). Sometimes also doing the "idle hunt" at a stop, with engine warm. I thought I finally fixed this with a $30 part. Note that all TPS modules for this car are not adjustable - no slotted mounting holes. The dealer wants well over $100 for the same part. Looking at online for OEM replacement TPS sensors, I can get a new Delphi OEM TPS for about $95. With no idea if this is a Hall Effect sensor or not.

So, now for the question(s). Is there a software change possible on an advanced OBDII / OBDIII reader so that the computer recognizes the two types of TPS sensors? Both (potentiometer and Hall effect) seem to work ok on my car (original vs replacement), but I'm guessing the specification voltage curve over the rotational position range is different, probably in the 10ths of volt, but enough make a difference. Also, some possible software compensation for a hysteresis in the Hall Effect TPS that is not possible with a good potentiometer. That compensation would make sense to me. Computer expects a Hall effect, and is reading a potentiometer instead. And finally, is going to a mechanic to have this software set (if possible) in the computer going to cost me more than getting a $100 OEM TPS?

This thing driving (no pun intended) me nutzo! If possible, copy your response to my eamil.

Thanks! Doug aka - snarlson_carlson

Comments (1)
No. 1-1


I would start with an oem tps, and if not that, load test the wiring to the computer closely, cause if not that, computer is shot .