P0122 troubleshooting

Hi i have been having trouble passing emissions on my jeep for the past couple years lol. now that i have fixed all the emissions system leaks this is the last code left. i don't have a check engine light but i have the P0122 code. I have a scan tool that shows TID:$51 CID:01, TID:$52 CID:01, TID:$53 CID:01 in mode 6. all read 0/out of there respective values. I just replaced the iac valve a few min ago and it changed TID:$62 CID:01 from red to green. anybody have a similar issue. Anybody know what the purge flow system monitor is i have no clue. i have a 01 xj.

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P0122 JEEP Code - Throttle Position Sensor Circuit Low Input

P0122 JEEP code possible causes
- Faulty throttle position sensor (TPS)
- Throttle position sensor wire harness is open or shorted
- Throttle position sensor circuit poor electrical connection


Test and inspect the TPS wire plugs and wires. Look for corroded, bent or pushed back wire plug pins and chafed, melted or damaged wire insulation. Clean all the related wire plugs and engine bay ground locations.

Test the TPS. TPS failure is somewhat common. Install a new genuine Jeep TPS if necessary. Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a "Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep engine sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts. Cheap parts are cheap for a reason.


TPS Testing

The TPS is mounted on the throttle body. The TPS is a variable resistor that provides the Powertrain Control Module (PCM) with an input signal (voltage) that represents throttle blade position. The sensor is connected to the throttle blade shaft. As the position of the throttle blade changes, the resistance of the TPS changes. Along with inputs from other sensors, the PCM uses the TPS input to determine current engine operating conditions. In response to engine operating conditions, the PCM will adjust fuel injector pulse width and ignition timing.

The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the PCM) represents the throttle blade position. The PCM receives an input signal voltage from the TPS. It is best to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts. 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.

The TPS is sensitive to heat, moisture, and vibration, leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced. A TPS may fail gradually leading to a number of symptoms which can include one or more of the following:

• Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".
• High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction with a slow engine return to idle speed symptom.
• Slow engine return to idle: A failing TPS can report the minimum throttle position values incorrectly which can stop the engine entering idle mode when the throttle is closed. Normally when the throttle is closed the engine fuel injectors will be deactivated until a defined engine RPM speed is reached and the engine brought smoothly to idle speed. When failing a TPS will not report the throttle closed and fueling will continue causing the engine to return to idle very slowly.
• Engine Hesitation on Throttle Application: The TPS is also used by the ECU to determine if the driver has applied the throttle quicker than the Manifold Air Pressure sensor can read. The fueling is adjusted accordingly to cope with the sudden increase in air volume, however a faulty sensor can cause the ECU to ignore this data and the engine will "hesitate" when applying the throttle. In extreme cases with the engine at idle, a sudden application of full throttle can stall the engine.
• Engine Misfire: A fault TPS can report values outside the acceptable range causing the ECU to incorrectly fuel the engine. This is noticeable as a slight misfire and can trigger the misfire detection software and/or Malfunction Indicator Lamp (MIL) light on the dashboard. Extreme cases can cause excessive misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.

I went ahead and tested voltage with a sewing needle from the middle wire to the negative terminal at the battery and got about 1 volt at idle and about 3.5 at wide open. I have a analog meter coming tomorrow but in the meantime i used a digital. Because the voltage is higher than the min and lower than the max, I'm assuming its a short somewhere. all the connectors in my engine bay are filled with dialetric grease if that causes anything that you are aware of but I wouldn't think so. i replaced the tps with a shit one untill i can getahold of a oem replacment. at one point i was messing with the plugs while it was running and i sprung a p0123 code and the check engine light came on but the p0123 code went away after a few min. any idea where a short could be? a buddy told me his clock spring went bad and caused similar issues but my horn works fine

The TPS operating voltages should be as specified. If the input is 5 volts, and you are not getting the specified output of .25 volts at minimum throttle opening (idle), to 4.5 volts at WOT wide open throttle the TPS is either Chinese garbage, or faulty.

If the TPS is not genuine Jeep, I would say that is root cause of the symptoms.



TPS clockspring issues happen rarely, but suspect the TPS quality first. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts.


A Jeeper had CEL 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 ground are shared inside the PCM.

CORRECTION: Replace the Clock spring assembly. Once the Clock spring has been replaced be sure to check the sensor 5 volt 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.

i just installed a oem mopar tps and the issue remains. Took awhile to show up. Any other ideas? I have a sneaking suspicion its emissions related because the emissions parameter test wont run but all other test run and pass

Sounds like a wiring problem.

Sounds like a wiring problem.

I just finished tearing the wiring harness apart from the tps to the computer yesterday and didn't find any shorts. Could the short be at a different sensors 5 volt supply? i tested again and found that my ground voltage at run and idle is .012v when spec is .015 to .02v. is that normal? could the computer be cooked?

i recleaned pins and noticed pin that was slightly off kilter that i missed befour. i bent them all up so there was a tighter contact and that fixed the problem. code went away

Don't you hate it when the simple stuff kicks you in the behind ?

I really do. hahaha. just gotta live and learn. thank you btw for all the help