How To Test The GM 2.4L Throttle Position Sensor (TPS)

TPS TEST 2: Testing The 5 Volt Reference Signal

The throttle position sensor (TPS) on your 2.4L Quad 4 vehicle needs power to work. This power comes in the form of 5 Volts DC from the fuel injection computer.

This test will help you to confirm if these 5 Volts are present or not. This is what you'll need to do:

1. 1

   Grab your multimeter and select Volts DC mode on it. You're gonna' test the gray (GRY) wire, this is the one that supplies power to the TPS.

2. 2

   Probe the wire that connects to the terminal labeled with the letter A (in the illustration above), with the red multimeter test lead and an appropriate tool (like a wire-piercing probe). The throttle position sensor's connector can be connected to the sensor or not when you probe this circuit.
   
   It's important that you do not probe the front of the connector or you run the risk of damaging the terminal.

3. 3

   Connect the black multimeter test lead to a good and clean Ground point on the engine or directly on the negative battery terminal.

4. 4

   When everything is set up, have a helper rotate the key to its ON position but don't start the engine.

5. 5

   The multimeter should display 4.5 to 5 Volts on its screen. OK, now let's interpret your test results below:

Let's interpret your test result:

CASE 1: The multimeter registered 4.5 to 5 Volts. This is the correct test result and it confirms that the fuel injection computer and the wire is supplying the TPS with power.

The next step is to test the Ground circuit of the throttle position sensor, go to: TPS TEST 3: Ground Circuit Test.

CASE 2: The multimeter DID NOT register 4.5 to 5 Volts. Then the computer or the wire are NOT providing the voltage that the TPS needs to operate.

The two most likely reasons for this are: 1) an open-circuit problem in the circuit or 2) the PCM may be fried. Altho' it's beyond the scope of this article to test these two conditions, you have now eliminated the throttle position sensor (TPS) on your GM 2.4L Quad 4 as being the cause of the problem and/or the TPS diagnostic trouble code (DTC) lighting up the check engine light (CEL).

TPS TEST 3: Ground Circuit Test

So far you have verified that the TPS is not creating a throttle position signal (TPS TEST 1) and that the TPS is getting power (TPS TEST 2).

The second step, before condemning the throttle position sensor, is to verify that it also has a good Ground.

NOTE: The PCM is the one that provides this Ground internally, so be careful and don't accidentally or intentionally apply power (12 Volts) to this circuit or you'll fry the PCM.

OK, here are the test steps:

1. 1

   With your multimeter still in Volts DC mode from TPS TEST 2.

2. 2

   Probe the black (BLK) wire, with the black multimeter test lead. The TPS connector can be connected or not to the sensor. This will be the wire that connects to the terminal labeled with the letter B in the illustration above.
   
   It's important that you do not probe the front of the connector or you run the risk of damaging the terminal.

3. 3

   Now, with the red multimeter test lead, probe the battery positive (+) terminal.

4. 4

   Once again, when everything is ready, have your helper turn the key to its ON position but don't start the engine.

5. 5

   If this circuit is OK and the PCM is providing a good path to Ground, your multimeter will display 10 to 12 Volts.

Let's interpret your multimeter test results:

CASE 1: The multimeter showed 10 to 12 Volts. This is the correct test result. It tells you that the PCM and the wire/circuit (that supply this Ground) are OK.

This multimeter test result also confirms that the TPS sensor is bad and needs to be replaced if you have:

• Confirmed that the TPS is not producing a signal that increases/decreases as you open/close the throttle plate (TEST 1).
• Confirmed that the TPS is getting 5 Volts (TEST 2) and Ground (TEST 3).

CASE 2: The multimeter DID NOT show 10 to 12 Volts. This indicates a problem with either the PCM (internal fault/problem) or an open in the wire between the TPS and the PCM itself.

Altho' testing these two conditions are beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) on your 2.4L Quad 4 vehicle as being the cause of the problem and/or the TPS diagnostic trouble code (DTC) lighting up the check engine light (CEL).

The TPS Code Won't Go Away

So you've tested the throttle position sensor (TPS) and according to the test results, the TPS is good. But the check engine light keeps coming back on even after you erased the diagnostic trouble code (DTC) from the computer's (PCM) memory. Well, here are a couple of suggestions that might inspire your next diagnostic move:

1. 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).
2. 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 pedal 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.
3. 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 intermittent problems 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.
4. 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.