The Throttle Position Sensor (TPS) is mounted to the throttle body and connected to the throttle plate shaft. The TPS is a potentiometer with a 5 volt reference input and a signal ground provided by the PCM. At a closed throttle position, sensor is low (approximately 0.5 volt). As the throttle plate opens, the output signal increases so that at wide open throttle, the output voltage will be high (approximately 5 volts).
See Figures 1 and 2
The TPS is a potentiometer attached to the throttle plate shaft. The PCM sends a 5 volt supply signal to the sensor and the percentage of the signal returned corresponds to the percentage of throttle opening, so that at Wide Open Throttle (WOT), the return signal should be approximately 4.9 volts.
- The sensor and signal voltages can be checked quickly using a voltmeter. Remove the air cleaner ducting as required to locate the sensor on the throttle body. First check the connectors and the wiring between the sensor and the PCM.
- Unplug the sensor wiring harness and connect an ohmmeter to terminal A and C on the TPS. Resistance should be above 200 ohms and should change smoothly as the throttle is moved.
- Connect a voltmeter between connector terminal A and ground. With the ignition switch ON , but the engine not running, there should be 5 volts, which is the supply signal directly from the PCM.
- Turn the ignition switch OFF and check for continuity to ground at terminal B on the connector.
- Reconnect the wiring and install a diagnostic connector, Saturn diagnostic probe or a voltmeter on the blue wire leading to terminal C and to ground. With the ignition switch ON but the engine not running, the voltage should change smoothly from about 0.4-4.7 volts as the throttle is moved from idle to full throttle.
A suitable scan tool such as the Saturn PDT can be connected to the ALDL and used to monitor TPS output, instead of attaching a probe to the wire.
REMOVAL & INSTALLATION
See Figure 3
- As an added safety precaution, you may wish to disable the air bag(s). refer to Chassis Electrical for the disabling procedure.
- Disconnect the negative battery cable and remove the air cleaner assembly.
- Unplug the electrical connector from the TPS.
- Remove the TPS retaining bolts, then remove the sensor from the throttle body.
- Make sure the throttle valve is closed, then install the TPS to the throttle shaft.
- Rotate the sensor counterclockwise to align the mounting holes, then install the retaining bolts and tighten to 18 inch lbs. (2 Nm).
- Connect the wiring harness to the sensor.
- Install the air cleaner assembly and connect the negative battery cable.
- If necessary, enable the air bag(s). refer to Chassis Electrical .