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TPS high voltage at idle position

glenmac

NAXJA Forum User
Location
Seattle
My 1999 XJ 4.0L stick has CEL on and gives codes P0123 and P0113.
With the key on, TPS has 5.2 V input. But output is 1.85-1.93 V with throttle closed and WOT reads just over 4 V. Swapped in my old replacement TPS and got same reading for fully closed throttle body.

Could this be 2 crappy TPS units (different brands)?
What can cause such a high reading from the TPS when throttle is closed?

Checked wiring: disconnected battery, unplugged MAP, IAT and TPS and the C1 connector from PCM. Ground to PCM #4 is 0.5 ohms for all three sensors. TPS output is open to #23 and no readings to any other pin on the PCM connector. All of those sensors have been recently replaced. Also cleaned ground connections to body and engine, including the grounds near the PCM.


Thanks,
Glen
 
Cheap crappy "Lifetime Warranty" parts are often out of specification or even failed right out of the box. Many times they have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep sensors.


Also try unplugging the horn relay. Clock spring failure can cause stray voltage for the TPS because they both share a common ground.

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 5volts. This will vary in an approximate range of from .25 volts at minimum throttle opening (idle), to 4.8 volts at WOT wide open throttle.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.





TPS failure may have one or more of these Physical Symptoms:

1) The engine loses power and is stalling.

2) The engine will idle, but may die as soon as you press the gas pedal. When driving, it seems as if all power is gone.

3) Sometimes it feels as if the transmission is failed or isn't shifting properly, if at all. If you quickly jump on the gas you might be able to get the transmission to shift, but it won’t shift properly by itself. Shifting manually, the transmission goes through all the gears.

NOTE: The throttle position sensor is also DIRECTLY involved with transmission shifting characteristics. The TPS function should be verified early in the troubleshooting process, when a transmission issue is suspected.



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 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.
 
Last edited:
thanks,
Replaced the clockspring already. After replacing TPS, ÇPS,IAT, MAP, AIC, clockspring, PCM and fuel pump one at a time, it idles, no longer shuts off randomly, but hesitates when pushing on the throttle. And keeps showing those codes. Maybe I will try another TPS.

Glen
 
Okey then, replaced the Standard TPS with an Echlin. voltage with throttle closed is still high at 1.77 V. Is it possible that particular PCMs have give high idle voltages?
the CEL codes are for high voltages on TPS and IAT.

what is the best tape to rewrap wire bundles if I cut them apart to trace individual wires?

I'm at a loss here, any suggestions?

Thanks,Glen
 
I only buy genuine Jeep CPS and TPS. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured with genuine Jeep repair parts.

Cheap parts are cheap for a reason.
 
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