1.3b) TPS Throttle Position Sensor faultsSymptoms of faulty TPS:
Associated OBD2 error codes DTCs: P0121 - P0123
Note: - With the TPS disconnected the ECU depends on the slower signals it receives from the Mass Air Sensor (MAS) and/or the Manifold Air Pressure (MAP) sensor along with feedback from the oxygen sensor to help regulate engine speed and fuel injection cycle. How to check? The socket for electrical connection with the TPS has 3 pins, one for 'ground', one for 5 volts 'reference' and a third (generally the middle one) for 'signal' output. Back probe the signal pin in the connector to the TPS. Attach the positive lead of a voltmeter to the probe and measure the voltage output as the throttle plate is rotated. If working correctly the meter should show a voltage consistent with the throttle position from approximately 1 volt when closed and 5 volts when fully open. What is looked for is smooth voltage increase with throttle change.If there are drop outs in the throttle transition voltage signal or if there is no transition then the TPS is faulty. How to fix? If the track is dirty causing drop outs, try cleaning it with residue-free electrical cleaningspray. If the track is worn it is perhaps easiest toreplace the complete device. In some instances it may be possible to adjust the location of the central mount of the TPS contact arm along the throttle shaft by a few millimeters and in the process cause a fresh concentric region of track to be used
- Poor starting: The engine may start and then stall immediately.The engine may be encouraged to keep running by slowly pressing the accelerator pedal: pressing too quickly may again stall the engine.
- Erratic/fast idling: The idle may be so erratic as to have some impact on the automatic gear shift characteristics and may actually prevent gear shifts. The engine idle speed may be increased above normal if the TPS fails to report that the throttle is closed. After the engine has been run at high speed the engine may take longer than is usual to return to idle as the ECU will not be able determine how quickly to shorten the injector cycles.
- Engine hesitancy/ jump in revs: Engine may fail to respond quickly to the accelerator pedal input or may suddenly jump in revs inappropriate to pedal movement. When working properly the TPS should instantaneously signal the rapidly opened throttle position to the ECU. The speed of this signal is much quicker than any similar signal sent from Manifold Air Pressure (MAP) sensor or MAF/IATequivalent. The ECU responds by increasing the fuel injection volumes to match the rapid increase in air volume. If the TPS fails to send the correct signals, the engine will seem to "hesitate" as the throttle is applied as the ECU looks to the other (slower) sensors to determine engine status. A sudden blip of the accelerator at idle can stall the engine (see above - poor start) as the ECU reacts too slowly to increase the injection time to match the sudden intake of air.
- Engine Misfire: Spurious, beyond normal range, signals from the TPS causes the ECU to set inappropriate fuel injection cycles resulting in misfire.Detected misfire leads to a check engine light(CEL); mal-function indicator lamp (MIL). Cylinders with misfire events detected by the knock sensor may be shut down (disable specific injectors) by the ECU to prevent engine damage.
NEXT 1.4) Idle Air/speed control valve