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.
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.
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.
NOTE: Start and warm up the engine before testing the TPS signal voltage. Once the engine has reached its operating temperature, turn it off.
IMPORTANT: The throttle position sensor must remain connected to its electrical connector for this test to work. You'll need to use a back probe on the connector or a wire piercing probe on the wire. You can see an example of this tool here: Wire Piercing Probe.
OK, let's start testing:
Place your multimeter still in DC Volts mode.
Connect the red multimeter test lead the wire labeled with the number 1 in the photo. This should be the blue (BLU) wire of the TPS connector.
Connect the black multimeter test lead directly on the battery negative (-) terminal.
Turn the key to its ON position, but DO NOT start the engine.
Your multimeter should register between 0.5 to 0.9 Volts DC. This voltage value should not be jumping up and down but should remain steady.
Manually opent 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.
At wide open throttle, you should see 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.
Have your helper lightly tap the TP sensor with the butt of a screw-driver's handle (or something similar).
Slowly open and close the throttle plate as your helper taps the TP sensor.
The tapping should have NO effect on the multimeter voltage readings.
Repeat this (tapping the throttle position sensor) several times to make sure of your results.
Let's interpret your TPS signal voltage test:
CASE 1: 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.
If you still have a TPS trouble code lighting up the check engine light, this section will have a few more suggestions as to what could be causing the problem: TPS Code Won't Go Away.
CASE 2: 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.
TPS Code Won't Go Away
So you've tested the TPS per the instructions in this tutorial and according to the test results, the TPS is good, yet the check engine light is still on. Well, here are a couple of suggestions that might inspire your next diagnostic move:
- The throttle plate's idle-stop screw's factory adjustment has been altered so that the engine could be idled up and mask a miss/misfire and/or rough idle. This increases the TP sensor's signal to the PCM. The PCM doesn't like it and lights up the check engine light (CEL).
- The throttle cable is binding and causing the throttle plate to not fully close.
- This can be verified by simply having someone inside the vehicle pushing the accelerator cable to the floor and releasing it, with the engine OFF, while you visually check that the throttle plate and cable are not getting stuck somewhere in their travel.
- The TPS is failing intermittently. Which means that it works fine most of the time, but every now and then it doesn't:
- I have found that the best way to test these intermittents is to road-test the vehicle with the multimeter hooked up to the TP signal Wire with a long wire so that I can comfortably observe the signal going up and down as I or someone else drives.
- The TP sensor's connector is bad, usually the locking tab is broken and the connector has worked itself loose, causing an intermittent false connection.
If this info really saved the day, buy me a beer!