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by Bob O’Neill and Bob Lincoln
The Throttle Position Sensor (TPS) is mounted on the throttle body opposite the throttle cable. It connects to the throttle butterfly shaft; as the throttle opens and closes, the resistive wiper in the TPS changes the voltage reported to the ECU (computer).
Three wires connect the TBS to the harness; one receives 5 volts (DC) from the ECU and one is grounded. The middle pin returns a varying voltage to the ECU; this voltage is called the throttle position signal, and it should be between .16 volts and 4.7 volts, DC. If it is not, the ECU registers fault code 24, lights the power-limited light, and puts the entire system into limp mode. Then, the ECU estimates the throttle position from the values given by the MAP sensor.
On older cars, it can be very difficult to remove the TPS.
Defective Throttle Position Sensor (TPS) – To test the TPS turn the engine off, disconnect the sensor, and connect an ohmmeter (an undamped analog one may work best) between the center and either outside pin of the sensor. Slowly open, then fully close, then fully open the throttle. If the sweep of the meter’s needle jumps around at all, replace the TBS.
If the meter sweep is smooth when testing the TBS, connect the meter and test for 5vdc from one wire and ground on the other outside wire. To test for proper voltage from the center wire, reconnect the connector to the TPS and turn the ignition key to ‘RUN’. Do not start the engine. Then with one probe to the ground wire and the other to the center wire check the output voltage from the TPS. It will be necessary to pierce the insulation of the wire to make contact with the conductor.
The voltage should vary as the throttle position is changed within the range of near 0vdc when closed to around 3vdc at WOT. At the connector use the ohm meter to test the ground wire for continuity to ground and the supply wire for 5vdc. If power is not present at the supply wire or if the ground wire isn’t grounded, check your harness.
Poor wiring or connection - Read the page ‘How to troubleshoot drivability issues’. Check the wiring and connections between the sensor and the logic module. Check the harness from the sensor to the computer. Inspect every connector. Clean and re-grease the connectors with dielectric grease.
Sensors, Switches, and Other Systems | Main Repairs Page | EEKs
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