(B) - Troubleshooting the TPS

The following is a list of vehicle symptoms which have been associated with the TPS, but can also be related to other vehicle components.

^ Check engine light
^ Stalls/quits
^ Hesitation/stumble
^ Fast idle

If an EEC error code has identified the TPS as suspect, perform PC/ED Manual pinpoint tests on the TPS.

Testing the TPS in the vehicle electrical circuit:

The TPS is supplied with a 5.0 volt reference signal. As the TPS senses throttle plate rotation, the output voltage changes to a value in the range of 0.4 volts to 4.8 volts depending on vehicle application. A voltmeter, New Generation Star Tester (NGS) or Service Bay Diagnostics System (SBDS) is the recommended test equipment for checking the TPS output.

The reason SBDS or NGS are the preferred tools is that they allow TPS voltage monitoring without disturbing the connector. Many conditions can be caused by loose, dirty, oxidized, or poor connections that may correct themselves for a short time if the connector is disturbed during testing. This can mislead technicians into replacing a TPS that is okay, and the true cause, a bad connection, may return at some future time.








Measuring the TPS voltage at idle is key when diagnosing a TPS since most of its operational life is within 10 degrees of idle. Figures 2 and 3 include a guide to TPS output voltages for 1993-95 model year vehicles.





Figure 1 is a graph that shows how the TPS output voltage changes between engine idle and WOT conditions.

The TPS voltage increases when the throttle is depressed. Idle is typically in the 0.4 volt to 1.2 volt range. (Refer to idle voltage range chart.) As the TPS senses plate rotation toward Wide Open Throttle (WOT), the voltage increases. WOT is typically in the 4.0 volt range. A voltmeter, NGS, or SBDS is the recommended test equipment for checking the TPS output.

CAUTION:
MANY VOLTMETERS WILL AUTOMATICALLY CHANGE RANGES WHEN MEASURING TPS OUTPUT FROM IDLE TO WOT. WHEN A VOLTMETER IS USED TO MEASURE TPS OUTPUT FROM IDLE TO WOT, THE METER SCALES OR CHANGES RANGES AUTOMATICALLY. THERE MAY BE AN ERRONEOUS METER DISPLAY UNTIL THE VOLTMETER HAS LOCKED TO THE APPROPRIATE VOLTAGE READING. THE ERRONEOUS METER DISPLAY DOES NOT REPRESENT A DEFECTIVE TPS.

NOTE:
IT IS RECOMMENDED THAT THE "RANGE LOCK' FEATURE ON MANY METERS BE SET FOR CHECKING TPS VOLTAGE.

Use the 0.00 range to measure TPS voltage.

If your voltmeter does not change ranges automatically and the meter is set to millivolt scale when reading full range voltages, the meter display may not indicate a valid value. This can be misinterpreted as an open circuit or suspect TPS. Ensure the meter is set to volts for measuring full range voltage levels.