'98 XJ p0123 help, TPS high voltage

[CSThompsy12]

Hello,

On my 98 XJ 4.0 I am having a TPS problem. I am getting a code for p0123 (High TPS voltage)

I have put a new TPS on it, but that did not fix it. I put my scanner on it, and I am getting about 60% TPS position with the throttle on the idle position. I am getting the same with the old TPS. I have a second good running '99 XJ and which I checked the TPS % in idle position, and it was around 16%.

I even took the TPS off the throttle body and turned it by hand and watched the scanner. The percentage in this test ranged from 53% ate idle up to 100% at WOT. Same with the old TPS. Smooth increase in % throughout the range.

I did verify that the throttle flap is moving correctly. Currently the XJ does not want to start consistently. If it does it will High idle at 2500 RPM or more.

I've been doing some reading, but wondering where to look next.

 

[lawsoncl]

That sounds like a bad ground to the sensor. Use your meter and verify that you have a good ground from the sensor connector to the engine block or battery negative. It should be under an ohm to ground. If it's not, check the connections at the ground stud on the passenger side of the engine that holds the transmission dipstick. If it looks cruddy, remove and clean all the connections. Worst case, just add a new wire ground wire at the sensor.

Looking at the 1999 FSM
Pin 1 - Brown/Yellow wire is ground
Pin 2 - Orange/DrkBlue = Signal
Pin 3 - Orange = 5-volt supply

 

[Tim_MN]

TPS is the primary suspect.

Genuine Jeep TPS or cheap crappy Chinese clone TPS ?

 

[lawsoncl]

TPS is the primary suspect.

Genuine Jeep TPS or cheap crappy Chinese clone TPS ?

True, cheap sensors have been known to be bad out of the box, but both his old and new are doing the exact same thing. Easy enough to test everything with a meter though.

 

[CSThompsy12]

That sounds like a bad ground to the sensor. Use your meter and verify that you have a good ground from the sensor connector to the engine block or battery negative. It should be under an ohm to ground. If it's not, check the connections at the ground stud on the passenger side of the engine that holds the transmission dipstick. If it looks cruddy, remove and clean all the connections. Worst case, just add a new wire ground wire at the sensor.

Looking at the 1999 FSM
Pin 1 - Brown/Yellow wire is ground
Pin 2 - Orange/DrkBlue = Signal
Pin 3 - Orange = 5-volt supply

Thanks, I will definitely check this..

 

[CSThompsy12]

TPS is the primary suspect.

Genuine Jeep TPS or cheap crappy Chinese clone TPS ?

Standard Motor Products brand off RockAuto. Not the cheapest one, not most $ either.

I guess I could also take the one that is on my good running '99 Jeep and try it on this one I am having trouble with.

 

[CSThompsy12]

Been doing some TPS testing, etc.. and I want to update where I'm at. I need expert help lol.

I back probed the TPS connectors. I got the correct 5V across the ground network wire and the 5V supply wire (the two outside wires)

Ohm'ed out TPS ground to battery ground.

I then measured the output coming out of the TPS (center wire) I took quick a video of that.

https://youtube.com/shorts/c8c4EMy0PMM?feature=share

Throttle closed the output voltage is 1.17, which is a little higher than the max spec of .95. It was smooth throughout the range.

Everything seems at least close to factory spec. One interested thing was with the key off the test procedure said there should be 0 voltage on the center wire. I got .2V on that center wire with key off.

It still idles high with the TPS connected. It will actually idle down to about normal when I disconnect the TPS plug. It still shows almost 70% on the scanner with the TPS in idle position, key on.

As I said before, I have a good running '99 XJ. Would it be worth swapping the PCM's? Kind of stumped now.

 

[CSThompsy12]

Everything seems at least close to factory spec. One interested thing was with the key off the test procedure said there should be 0 voltage on the center wire. I got .2V on that center wire with key off.

EDIT, not .2V on the center wire. It meant on the outside orange 5v supply wire.

 

[lawsoncl]

I'm wondering if the signal wire back to the PCM is broken or damaged. I haven't measured it myself, but others have noticed that the voltage on the signal wire with it unplugged from the TPS sensor floats about 4 volts. Usually I reply that's irrelevant, but not seeing voltage might be a sign that wire is broken upstream.

You saw some changes moving the throttle, so maybe not completely broken but high resistance?

 

[CSThompsy12]

I'm wondering if the signal wire back to the PCM is broken or damaged. I haven't measured it myself, but others have noticed that the voltage on the signal wire with it unplugged from the TPS sensor floats about 4 volts. Usually I reply that's irrelevant, but not seeing voltage might be a sign that wire is broken upstream.

You saw some changes moving the throttle, so maybe not completely broken but high resistance?

Did a couple more tests based on what you said, thank you... I unplugged the TPS and and put the meter the plug. Put black meter lead on the TPS ground terminal and red lead on center orange/black terminal (signal to PCM) and got 5.6 volts. Should that one have voltage with the TPS unplugged from it?

Then put the red lead on the outside orange wire terminal (5v supply from PCM). I got 5.1V on that one which is correct.

Than finally, I located the orange/blue tracer wire at the PCM plug. I probed the wire at that end to make sure it wasn't damaged between the TPS and the PCM. It checked out good, (read the same voltage there as it did at the TPS)
Let me know if this makes sense, and thank you.

 

[Tim_MN]

Throttle closed the output voltage is 1.17, which is a little higher than the max spec of .95. It was smooth throughout the range.

The TPS is out of specification.

The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the PCM) represents the throttle blade position. This will vary in an approximate range of from .25 volts at minimum throttle opening (idle), to 4.5 volts at WOT wide open throttle.

 

[CSThompsy12]

The TPS is out of specification.

The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the PCM) represents the throttle blade position. This will vary in an approximate range of from .25 volts at minimum throttle opening (idle), to 4.5 volts at WOT wide open throttle.

Yes, which must be why the scanner is reading a TPS percentage of 68% when the throttle is in the idle position?

I have sort of ruled out the actual TPS being the problem.. I have tried the original one, a new Standard Motor brand one, and one off my other good running XJ, and they all read the same.

Saw that other threads have mention the clock spring. Not sure if this would pertain to my situation. I don't have cruise, just horn and airbag.

 

[CSThompsy12]

Think I may have fixed it! I pulled the horn fuse and horn relay from the compartment down on the passenger side. This made the TPS % drop from about 69% to 18% in the idle position. So looks like it must be the clockspring that was throwing the voltage off?

Its running well, however I had to give just a little gas to keep it idling or it would quit. maybe it just has to learn to idle again? I know my other one would do that after the battery died...

 

[Tim_MN]

Clockspring TPS

A Jeeper had OBD-II Check Engine Light trouble codes P0123, 0122, and 0121, Installing a new genuine Jeep TPS sensor did not solve the codes or cure the symptoms. On the highway the driver noticed the cruise control didn’t work either, and the Jeep was sputtering/stalling, The turn signal was acting weird, sometimes it would turn on, sometimes not...sometimes it would blink 10 times a second like it had a bulb gone out. Others Cherokee owners report the odometer randomly goes blank. The cure to all the symptoms was a new clock spring.

COMPLAINT: TPS TROUBLE CODE WILL NOT CLEAR

A late model Jeep with a 2.5 or 4.0 liter engine and the AW4 transmission comes in with the “MIL” Check Engine Light illuminated and a complaint of late shifts. A scan reveals a code P0123, “TPS Voltage High”, is stored. The scan tools data list indicates that the TPS signal wire voltage is at 5.0 volts at closed throttle, and then ranges up to 11.5 volts. A back probe of the TPS signal wire (usually is an Orange/Dk Blue wire), shows 5.7 volts at closed throttle, with a similar rise in voltage as the throttle is opened. A check of the TPS 5 volt supply and ground circuit prove that both of these circuits are good.

A check of the TPS signal wire with the TPS disconnected shows the same 5.7 volts. Inspection of the wiring between the TPS and the PCM and TCM shows no faults. A replacement TPS does not cure the problem, neither does replacement of the PCM or TCM.

TESTING: Unplugging a faulty Clock Spring should return the TPS voltage to its’ normal readings. Or, you can remove the Horn fuse in your fuse block - this will remove the 12 VDC supply to the clock spring. Once the short circuit is temporarily disconnected, you should be able to reset the trouble code, and confirm you diagnosis of a faulty clock spring.

CAUSE: The Switch Sense circuit in the Clock spring in the steering wheel hub has shorted to battery voltage from the horn button circuit. When the Switch Sense Circuit shorts to the 12 volt HORN circuit the TPS signal voltage is driven high and remains there as shown. This is because the 5 volt reference voltage used by the Cruise Control “Switch Sense” circuit and the TPS are shared inside the PCM.

CORRECTION: Replace the Clock spring assembly. Once the Clock spring has been replaced be sure to check the sensor 5volt reference voltage at the PCM to insure that circuit has not been damaged by the short to power. Also check the TPS signal range to insure the TPS has not been damaged.

 

[CSThompsy12]

I see Dorman sells a clockspring on Rockauto. Is that good? or should I go oem. The Jeep purrrs now.

 

[lawsoncl]

I'm skeptical you can even find a real mopar one. I believe there are two different part numbers depending on whether you have cruise control or not.

 

[Tim_MN]

I have always rebuilt XJ Cherokee wrecks with airbags and clock springs from the salvage yard. In some clock spring threads, I have read people used Dorman with no problems. There are two part numberss as mention above.

The TJ Wrangler uses the same clock spring, so you might find a genuine Jeep part that way.

 

[Unclewolverine]

I have a spring from a zj with an airbag in my non air bag 95, cruise works perfectly.

 

[Tim_MN]

1997-2001 airbags and clock spring do not interchange with 1996 and older.