There are a few items you should check before getting into more in-depth testing.
- Check for a skewed MAP signal or faulty MAP sensor. An incorrect MAP signal may cause the PCM to incorrectly calculate the predicted TP sensor value during high engine load situations. A qualified technician using a Scan Tool will want to check for an abnormally low MAP reading.
- Check for poor connection at the PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections.
- Look for a damaged harness or damaged wiring going to the MAP sensor, especially if heavy work has recently been done where the connector could have been damaged.
- With the engine OFF and the ignition ON, check the voltage at the signal return circuit of the TP sensor by carefully backprobing the connector using a DVOM.
- Voltage should be between 0.2 and 1.4 volts at idle.
- Slowly move the throttle pulley to the wide open throttle (WOT) position and watch the voltage on the DVOM. The voltage should slowly rise to slightly less than 4.8v at Wide Open Throttle (WOT).
- If no voltage is present, check the wiring harness for supply voltage (5.0v) and ground (0.3v or less), by referring to your corresponding wiring guide. If supply voltage and ground are present, but no output voltage from TP, replace the TP sensor. If supply voltage and ground do not meet specifications, make necessary repairs to the harness or PCM.
The Throttle Position (TP) sensor is a potentiometer connected to the throttle shaft on the throttle body. It provides a voltage signal that changes relative to throttle blade angle. The signal voltage will vary from less than 1 volt at closed throttle to about 4 volts at Wide Open Throttle (WOT). By monitoring the voltage on the signal line, the PCM calculates throttle position. As the throttle valve angle is changed (accelerator pedal moved), the TP sensor signal also changes. At a closed throttle position, the output of the TP sensor is low. As the throttle valve opens, the output increases so that at WOT, the output voltage should be above 4 volts.
The PCM calculates fuel delivery based on throttle valve angle (driver demand). A broken or loose TP sensor may cause intermittent bursts of fuel from an injector and unstable idle because the PCM thinks the throttle is moving. A failure in the TP sensor 5 volt reference or signal circuits or ground circuit will set Diagnostic Trouble Codes (DTCs). Once a DTC is set, the PCM will use an artificial default value based on engine RPM and mass air flow for throttle position and some vehicle performance will return. A high idle may result when a circuit ground fault is present.
The PCM can detect intermittent TP sensor faults. The PCM can also detect a shifted TP sensor. The PCM monitors throttle position and compares the actual TP sensor reading to a predicted TP value calculated from engine speed. If the PCM detects an out of range condition, a DTC will be set.
Removal & Installation
- Disconnect the negative battery cable.
- Remove the air inlet tube to access the throttle body.
- Detach the TP sensor electrical connector.
- Remove the TP sensor screws and carefully pull the sensor from the throttle shaft stub end.
Typical Throttle Position (TP) sensor mounting
- With the throttle in the normal closed idle position, install the TP sensor on the throttle body assembly
- Apply a suitable thread-locking compound to the TP sensor attaching screws, install the screws and tighten to just 18 inch lbs. (2 Nm).
- Install the air inlet tube.
- Connect the negative battery cable.
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