TEST 3: Testing The Throttle Position Sensor Signal
So far all of your tests have confirmed that the TPS sensor on your GM car or pick up is getting both power (5 Volts) and ground. Now, for the test you signed up for, testing the throttle position sensor signal.
As mentioned at the beginning of the article, this is the signal that tells the PCM how much the throttle opens when you step on the accelerator pedal.
You'll need a helper to assist you in this test step, since he or she will need to lightly tap on the throttle position sensor's body with a screw driver (or other appropriate tool) while you observe the multimeter and manually actuate the throttle. OK, let's start testing:
With your multimeter still in DC Volts mode from the previous tests.
Probe the wire (circuit) labeled with the number 1 in the photo with the red multimeter test lead, using an appropriate tool to pierce the wire. This should be the Blue wire of the TPS connector.
Ground the black multimeter test lead directly on the battery negative terminal.
Turn the Key On but DO NOT start the engine.
Your multimeter should display a specific Voltage value between 0.5 to 0.9 Volt DC. This Voltage value should not be jumping up and down but should remain steady.
Now that the multimeter is set up... manually rotate the throttle plate by hand as you observe the Voltage displayed on your multimeter.
The initial voltage reading should increase smoothly as you open the throttle plate to its Wide Open Position to about 4.5 to 4.9 Volts.
Now, slowly release the throttle plate to its fully closed position, all the while observing the multimeter's reading.
The multimeter's voltage reading should decrease in a smooth and linear fashion and return to the initial voltage reading you observed at the beginning of the test.
OK, now have your helper lightly tap the TP sensor with the butt of a screw-driver's handle (or something similar).
As he or she taps, you need to slowly and smoothly open the throttle to its open-wide position and then slowly release it back to its closed position.
All the while you've got your eyes glued on the multimeter to see if the tapping affects the voltage readings.
Repeat this (tapping the throttle position sensor) several times to make sure of your results.
Interpreting The Results
If the throttle position sensor (TPS) is working correctly, the multimeter will register a smooth increase in the DC voltage until the maximum voltage is reached, which is about 4.5 Volts DC. Then, as you slowly release the throttle plate back to its closed position, the multimeter will display a gradual decrease in voltage till the initial base voltage is achieved (which you recorded in the beginning of the test).
If the TPS is BAD, then there will be sudden gaps/loss of voltage or the readings will jump about crazily as you increase or decrease the throttle plate's to its fully open or fully closed position, especially when you tap on the sensor. Or, there will be no voltage reading at all. OK then, here are the two possible outcomes:
CASE 1: If the multimeter registered a smooth increase or decrease in voltage. This test result tells you that the TP sensor on your GM vehicle is working OK and is not the cause of the TPS fault code issue. Go to TEST 4 for a few more suggestions as to what could be causing the TPS diagnostic trouble code (DTC).
CASE 2: If the multimeter DID NOT register a smooth increase or decrease in voltage. Then the throttle position sensor (TPS) is BAD on your GM car or pick up or SUV. Replacing the throttle position sensor will solve the TPS diagnostic trouble code (DTC) lighting up your check engine light (CEL) on your GM car or SUV.