Hi all,

working on my sons 1998 Cherokee with the 4.0 auto trans.

problem just started, running bad, felt like the trans was slipping. Checking codes I have po121 122 and 123. Also a po700.

I just checked the tps wiring. key on engine off shows 5.05 volts on the center connector with the throttle closed. That’s the signal wire that I believe should have about .45-.5 v throttle closed. That was back probing the tps connector while still connected.

removing the connector from the TPS and checking the connector side of the harness shows 4.68 v with Koeo.

The ground terminal and the 5v input side test fine. What should I be looking for? What would cause the high reading on the tps signal wire?

sweep test of the tps looked good

Recently I replaced the 3 transmission solenoids. That solved my trans problems. I’m not sure if it’s related. But it’s the only recent work done so I thought I should mention it.

Confused in NY

thanks,
Joe Walters

 

Hello,

I just reran some tests on the tps so and looked at live data. I figured I would add the info in hopes that it will help someone help me.

On pin 2, the signal wire.

the results were off. I got 5.05 volts with the throttle closed. And got 5.08 at wide open throttle. Both way out of spec.

The other result out of spec is on pin 3, the 5 v supply circuit. With the key off and throttle at idle I am seeing .029 volts. The specs I have say it should be .000
With the key on I am getting a good 5.12 volts, which I think is fine.

tests were ran with connector plugged into the tps and back probing the connector

The other thing I noticed when looking at live data is that the tps % is staying between 98 and 99.2% when running in park and reving the engine between idle and 3000 or so rpm.

I don’t do much of this kind of work. So I am confused at what to do next.

All help is much appreciated. My kid needs his Jeep.

thanks,

Joe Walters

 

Try removing the horn fuses and the airbag fuse just because it’s free and easy. Might not be it but it could rule it out. Also remove fuse for cruise control if it’s equipped.

 

thank you Waynerd. I will try that tomorrow and see if it changes anything.

 

I put these picture illustrations here just for referencing purposes. It sounds like you did the testing correctly. It can be done by probing either the connector ground wire or the chassis to the signal wire during testing procedures.

It sounds like there could be a fault occuring somewhere else to the sensor.. with possibilities being one or more of a several different reasons. Maybe it is the sensor itself though?

I believe one way to help verify wether or not the TPS is normal is to test the TPS sensor itself, by measuring for a sweep in Ohms with the sensor disconnected. It is kind of the same as how you check for a voltage sweep. Except, it is looking at the other side of the spectrum with what the sensor is doing internally to produce the signal. Disconnect the TPS. Probe the signal and ground portions of the sensor with a multimeter set to read resistance. In the same similar way when looking for a good consistantly sweeping voltage signal, you should see the same thing in Ohms when doing the test like this looking at resistance when opening the throttle (or, by moving that moving portion on the sensor yourself manually).

Any of the other 5 VOLT sensors are able to interfere with one another. You can repeat the signal wire circuit voltage sweep test at the TPS to see if it changes to return back to normal after unplugging each one of the other 5 VOLT sensors one by one (MAP, IAT, ECT).

The clockspring in the steering column has been known to often cause electrical noise and Interference on the associated circuitry of the TPS to PCM interface. It causes the PCM to misinterpret and distort the TPS signal, and may cause an electrical spike to occur at the TPS. Disconnecting the clockspring would result in having a normal TPS signal voltage if this were the reason.

A short to power somewhere in the wiring could do this causing an abnormal voltage to occur on the TPS signal.

Possibly, it could be an internal fault of the PCM itself is another reason.

 

👽

 

what do the codes you quoted say is wrong ? so we can advise

If you have 5V on the sender wire of the TPS, very high chance TPS or wiring is shorted

 

Just so you'll know, I shorted out my TPS by pouring Seafoam down the throat of the throttle body. It seems some got thru the shaft seal.

 

Yep, I toasted one too back in the day with seafoam. Nevermore!

 

good morning,

that is the diagram I used for testing. I think I did it right.

I did disconnect the tps connector to do the ohms sweep test. I put the positive lead on the signal terminal and the negative on the ground terminal.
i opened and closed the throttle slowly by hand several times. I was using a digital meter. Readings were smooth both directions, no drops or spikes noted.

I can hook my meter up to the signal wire and disconnect the sensors one at a time to see if the voltage changes. I will try to find a list of what’s on that circuit.

Waynerd suggested removing the fuses for the horn, airbags and cruise. It sounds like that will duplicate disconnecting the clock spring.
is that correct?

im hoping it’s not a short to power or a pcm issue.

thank you,
JoeW

 

Noah911
the sweep test I am referring to is the ohms test. Done by checking between the signal and ground terminals on the tps sensor itself.

I disconnected the harness and with the key on I had a reading of .009v on the ground wire.

I also hooked up my test light to the batt positive and touched the ground wire. The test light came on bright

the voltage sweep test of the signal wire showed 5.05v with the key on throttle closed. With the throttle open it went up slightly to 5.08v

With the harness connected and back probing the ground with the key on I got .010v. With the key off I got .000

Generally.. with having 5 VOLTS on the signal wire, and when the ground is showing as testing normal (less than 0.1 VOLTS), this indicates having a bad TPS due to the sensor itself is open internally

If I’m getting 5 v on the signal wire with the connector disconnected. Am I wrong in thinking that it can’t be the tps itself since it’s not connected?

thanks for your help on this.

Joe W

 

dave,

nothing like that has been done recently. But I’ll definitely keep that in mind in the future.

thanks,
Joe

 

im getting 5 v on the signal wire of the plug with the tps disconnected and connected

po121 is showing a higher voltage on the tps between circuits a & b
122 is tps low input of circuit a of the tps
123 is tps high circuit input
po700 is a generic transmission code

thanks,
Joe W

 

All of what you said sounds correct to me. With the testing results, I am going to take a stab and guess there is a short to power somewhere.

I think the Ohms sweep test may be good enough to state you successfully verified the TPS itself is not the likely reason, and is probably a good sensor. I am not 100% sure about this though but, it sounds right.

With the 5 VOLT sensors I believe the MAP sensor is the most likely of those to be the reason for seeing 5V on the TPS signal, as I believe it is the next in line to it, and this would make it a real live possibility. The MAP would be the one I pulled to check if I were wanting to confirm the other 5V sensors are not the reason. The other closely related 5V sensor to the TPS is the engine temperature sensor.

Yes, in a way pulling those fuses may help to eliminate the clockspring. However, there is conflicting information to say this is not necessarily the case depending, and that the only way to be sure is to actually disconnect the clockspring itself to be absolutely sure of this. I do not believe the clockspring is the reason for how you describe the symptoms and test results. An airbag CEL should be illuminated and the other electrical functions should also have malfunctions on them if the clockspring were going bad. If this was also the case, then definitely I would say it appears the culprit is the clockspring. The other defining characteristics of having a faulty clockspring do not absolutely have to occur to be able and cause electrical noise interruptions of the TPS signal with the PCM interface though, simply because of how the data-bus was set-up to run. There does not need to be an actual faulty clockspring...

With the reference signal being normal to the TPS, having shown normal ground tests at the sensor, and a normal Ohms sweep test.. there only seems to be three possible conclusions to draw; Influence from another 5 VOLT sensor, a short to power of the wiring, or the PCM has the TPS stuck in run-up test mode. As I understand it, the PCM does a quick calibration for its own referencing purposes serving a few different reasons - one of them being for storage and updates to the internal memory. As some of the sensors deteriorate with use and time, the PCM adjusts to this for maintaining a good up to date calibration. This is the reason why the TPS signal may be able to be stuck at wide open throttle related to a fault of the PCM. This is also the reason why if you ever replace a faulty TPS, you should definitely be resetting the PCM afterwords as a best practice guideline. If you do not reset the PCM after changing out a faulty TPS, the PCM will be calibrating a new good TPS from memory based off of crummy information obtained from the prior faulty sensors data. This is also the reason why after your TPS issue has been resolved, you too should also do the same and reset the PCM, provided it is not the PCMs fault in the first place.

 

Noah911,

I just went out and removed the horn relay and air bag fuses, couldn’t find one listed for the cruise. No changes in voltage at the signal wire at the connector.
does having the tps disconnected eliminate it as I suspect.

I also disconnected the iac, map, coolant temp switch, purge solenoid and the one on the intake. No changes.
i need to find a schematic to see what else is on that circuit. Do you happen to have one handy?

I can disconnect the trans computer when I go back out. I can disconnect the clock spring to be 100 % sure if you think I should.

how do I go about checking for a short to power and checking the pcm?

Also, with the po700 trans code. Does that tell us anything? Or is that normal when the tps circuit has a problem.
I just want to be sure that it’s not related to the trans solenoids I replace a couple weeks ago.

the solenoids took care of my trans problems and cleared the po743 code. He has put on about 400 miles since I did that.

i appreciate your patience and advise.
any other suggestions appreciated.

thanks,
Joe W