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TPS wiring issue?

MYJEEPISRUSTY

NAXJA Forum User
Location
Michigan
So I have a 1998 XJ 4.0 auto. a couple nights ago i hear the horn going off constantly. it was late and i was tired so i just unhooked the horn connectors in the front bumper and left it. the next morning on the way to work the jeep is dropping RPMs:laugh::laugh: after upshifting then going back up and running weird in general and throws a code along with the airbag light coming on. i get to work and scan the code and it is a p0123 TPS circuit voltage high code. i order a new TPS and throw it on and my problem is still there. same code same symptoms. so i do some research and learn that a bad clockspring can cause the tps issue due to the 2 items sharing a 5 volt reference. since my airbag light was on as well i figured this could be the problem and i order a new clockspring. well i just installed the clockspring and my airbag light went off but the code is still there. although now the code reads a p0122 TPS circuit voltage low. I still have the same symptoms as well. so would my next move be backprobing the TPS connector and checking grounds? why would the code change from voltage high to voltage low? thanks for the help in advance
 
Anytime you have a high voltage issue, start with new cables.
 
Fully charge the battery on a charger, low battery voltage causes all kinds of drivability issues.

Clear the trouble codes. See if any return. Test the TPS circuit for low input voltage, and test the TPS response.

Did you install a genuine Jeep TPS ? 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 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.

TPS TEST

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 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.

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 denied 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 excessing misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.
 
I tested my new TPS with a meter and found the orange power wire is getting its 5 volts but the orange/brown signal wire to the PCM is only sending out .06 volts at closed throttle and only goes up to .2 volts at WOT. this would mean the dorman TPS i got is bad correct? And I should replace it with an OEM Mopar part?
 
Yup.

TPS approximate range of .25 volts at minimum throttle opening (idle), to 4.8 volts at WOT wide open throttle.
 
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