How to Diagnose a Jeep Throttle Position Sensor

by Theresa C. England

The throttle position sensor (TPS) is used in fuel-injected and carbureted engines. The TPS is used to monitor the position of the throttle butterfly valve. When the car accelerates, the butterfly opens to allow air into the intake manifold. There are a few signs that could signal that the throttle position sensor is failing.

Step 1

Turn on the ignition to the "On" position, but do not start the car. Make sure the volt meter is on 12 volts DC. Locate the connector that goes from the ECM (engine control module) to the TPS and disconnect it from the TPS. There are usually three prongs; the center prong is normally the negative connector.

Step 2

Take the volt meter and connect the negative side (usually the black wire) to the ground terminal on the battery. Take the positive lead (usually the red wire) and attach it to one of the other prongs. The volt meter should read five volts if you have successfully found the reference wire for the TPS. If it reads anything below five volts, then you are on the signal wire and need to go to the other prong in the connector. If it reads nothing, then you are on the negative connector. If it reads five volts, then you know that you are getting proper reference voltage to the TPS. Therefore you have just eliminated a faulty power feed to ECM.

Step 3

Re-install the connector back on the TPS. Take the positive lead for the volt meter and put it to the signal wire in the back of the connector--this is known as "back probing." Take the negative lead from the volt meter and put it to the center wire (negative on the connector).

Step 4

Take the butterfly shaft and manually turn it. As you turn it, you should get a gradual count on the meter upwards to five volts. If the volts fluctuate backwards or forwards erratically, then you know you have a faulty TPS.

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