See Figure 1
The Throttle Position (TP) sensor is connected to the throttle shaft and is controlled by the throttle mechanism. A 5 volt reference signal is sent to the TP sensor from the ECM. As the throttle valve angle is changed (accelerator pedal moved), the resistance of the TP sensor also changes. At a closed throttle position, the resistance of the TP sensor is high, so the output voltage to the ECM will be low (approximately 0.5 volt). As the throttle plate opens, the resistance decreases so that, at wide open throttle, the output voltage should be approximately 5 volts. At closed throttle position, the voltage at the TP sensor should be less than 1.25 volts.
By monitoring the output voltage from the TP sensor, the ECM can determine fuel delivery based on throttle valve angle (driver demand). The TP sensor can either be misadjusted, shorted, open or loose. Misadjustment might result in poor idle or poor wide-open throttle performance. An open TP sensor signals the ECM that the throttle is always closed, resulting in poor performance. This usually sets a Code 22. A shorted TP sensor gives the ECM a constant wide-open throttle signal and should set a Code 21. A loose TP sensor indicates to the ECM that the throttle is moving. This causes intermittent bursts of fuel from the injector and an unstable idle. Once the trouble code is set, the ECM will use an artificial default value for the TP sensor, and some vehicle performance will return.
See Figures 2, 3 and 4
- Visually check the connector, making sure it is connected properly and all of the terminals are straight, tight and free of corrosion.
- With the ignition in the ON position, check the voltage at terminal B. The voltage should read less that 0.5 volts.
- Operate the throttle, while watching the voltage. The voltage should increase smoothly to 5 volts as the throttle is opened.
- If the voltage is not within specification, check the 5 volt reference signal circuit at terminal C and ground the circuit at terminal A for the proper signal. If the correct signal is found, the sensor is faulty. If the proper signal is not found, check the circuits back to the computer control module for continuity.
- If the circuits are functional, the PCM may be faulty.
REMOVAL & INSTALLATION
See Figure 5
- Disconnect the negative battery cable.
- For 3.8L (VIN 3 and C) engines, disconnect the PCV vent hose, then detach the TP sensor electrical connector.
For 3.8L (VIN 1, L and K) engines, perform the following steps, as necessary:
- Disconnect the manifold vacuum lines from the throttle body and fuel pressure regulator.
- Detach the IAC, TP sensor, MAF sensor electrical connector.
- If necessary, detach the EGR valve electrical connector.
- Unfasten the TP sensor's attaching screws, then remove the TP sensor from the throttle body.
- Position the throttle valve in the normal closed idle position, then install the TP sensor on the throttle body assembly, making sure the TP sensor pickup lever is located above the tang on the throttle actuator lever.
- Apply Loctite® 262 or equivalent threadlocking compound to the TP sensor screws. Install the TP sensor retainer and attaching screws. For 1987-91 vehicles, do not tighten the attaching screw until the TP sensor is adjusted, as outlined later in this section.
- If not already done, tighten the TP sensor screws securely.
- For the 3.8L (VIN 3 and C), attach the PCV vent hose.
- For the 3.8L (VIN 1, L and K) engines, perform the following steps, as necessary:
If removed, attach the EGR valve electrical connector.
- Attac the IAC, TP sensor and MAF sensor electrical connectors.
- Attach the manifold vacuum lines to the fuel pressure regulator and throttle body.
- Attach the TP sensor electrical connector.
- Connect the negative battery cable.
If a Tech 1® or equivalent scan tool is available, it is advisable to use the scan tool to read the TP sensor voltage. If using a voltmeter, extreme care must be taken to probe the correct terminal carefully. Incorrect TESTING or probing can damage the TP sensor connector or destroy the ECM.
- With the TP sensor attaching screws loose, install 3 jumper wires between the TP sensor and harness connector.
- With the ignition switch ON , use a digital voltmeter connected to terminals B and C and adjust the TP sensor to obtain 0.33-0.46 volts.
- Tighten the attaching screws, then recheck the reading to insure the adjustment has not changed.
If the TP sensor is only being adjusted, remove the screws, add threadlocking compound (Loctite® 262, or equivalent), then reinstall the screws.
- With the ignition switch OFF , remove the jumper wires and connect the harness to the TP sensor.