How To Test The GM Accelerator Pedal Position (APP) Sensor 1

TEST 2: 5 Volt Reference Circuit Test

The second thing we need to do now, is to make sure that Accelerator Pedal Position (APP) Sensor 1 is getting power. This power is in the form of 5 Volts DC and is provided by the Throttle Actuator Control (TAC) Module.

The wire that you'll be testing is the White w/ Black stripe wire that feeds the pin labeled with the letter G of the APP Sensor Assembly.

IMPORTANT: The image, above, shows you the front of the connector just to make it easier to identify the circuit you need to test. When testing the circuit, you should back-probe the connector or probe the wire (with a wire-piercing probe), or you could damage the metal female terminal! This is a headache you definitely want to avoid.

Alright, this is what you need to do:

1. Locate the wire on the APP sensor connector (inside the vehicle) that belongs to circuit G.
   • You don't have to have the APP Sensor Assembly bolted in place (in the vehicle) or connected to its connector for this test. If you do, this test info still applies.
   • The APP Sensor Assembly connector has the letter G embossed on it, to further aid you in identifying it.
2. Place your multimeter in Volts DC mode.
3. With the red multimeter test lead, probe the wire identified with the letter G.
   • This is usually a White w/ Black stripe colored wire.
   • NOTE: If the wire is a different color, identify the wire by the letter that's embossed on the connector.
4. Ground the black multimeter test lead directly on the battery negative (-) terminal.
5. Have a helper turn the key ON, but don't crank or start the engine.
6. If all is OK, your multimeter should register about 5 Volts.
7. Let's interpret your test results below:

Let's analyze your test results:

CASE 1: Your multimeter registered 5 Volts. So far so good, since this test result lets you know that Accelerator Pedal Position (APP) Sensor 1 is getting power.

The next step is to check that Accelerator Pedal Position (APP) Sensor 1 is getting Ground. Go to: TEST 3: Reference Low (Ground) Circuit Test.

CASE 2: Your multimeter DID NOT register 5 Volts. Double check your connections and make sure you're testing the correct wire.

If your multimeter still does not register 5 Volts in this circuit, then you've found the cause of the Accelerator Pedal Position (APP) Sensor 1 diagnostic trouble code (DTC). Repair the issue causing these missing 5 Volts, since without power APP Sensor 1 won't function.

Now, although it's beyond the scope of this tutorial to troubleshoot these missing 5 Volts, here are the two most like causes:

1. There's an open-circuit problem in this wire between the APP Sensor Assembly's connector and the Throttle Actuator Control (TAC) Module.
2. The Throttle Actuator Control (TAC) Module is bad.

TEST 3: Reference Low (Ground) Circuit Test

So far in your troubleshooting, you have:

• Resistance tested Accelerator Pedal Position (APP) Sensor 1 (TEST 1).
• Checked for the 5 Volt Reference signal. (TEST 2).

Now, we're gonna' test the Ground circuit (also know in GM tech terms as the Reference Low Circuit).

This Ground, like the 5 Volts you tested in the previous test, is provided by the Throttle Actuator Control (TAC) Module. This means that you need to be careful to NOT short this circuit to 12 Volts intentionally or accidentally or you're gonna' fry the TAC Module.

The wire that you'll be testing is the Brown (or Yellow w/ Black stripe) wire labeled with the letter E in the photo below.

IMPORTANT: The image, above, shows you the front of the connector just to make it easier to identify the circuit you need to test. When testing the circuit, you should back-probe the connector or probe the wire (with a wire-piercing probe), or you could damage the metal female terminal! This is a headache you definitely want to avoid.

Alright, this is what you need to do:

1. Place your multimeter in Volts DC mode.
2. With the black multimeter test lead, probe the wire identified with the letter E in the photo below.
   • This is usually a Brown colored wire of the connector.
   • Note: If the wire is a different color, identify the wire by the letter that's embossed on the connector.
3. Connect the red multimeter test lead directly on the battery's positive (+) terminal using a battery jump start cable.
   • NOTE: The jumper cable will be 'live' with 12 Volts, so be careful and wrap the jumper cable end (that you've brought into the vehicle) in a shop towel or plastic bag. This will keep it from shorting to any metal surface.
4. Have a helper turn the key ON, but don't crank or start the engine.
5. If all is OK, your multimeter should register 10 to 12 Volts.
6. Let's interpret your test results below:

Let's take a look at what your test results mean:

CASE 1: Your multimeter registered 10 to 12 Volts. So far so good, since this test result lets you know that the Throttle Actuator Control (TAC) Module is providing Ground to Accelerator Pedal Position (APP) Sensor 1.

The next step is to check that APP Sensor 1 is creating the correct pedal position signal. Go to: TEST 4: Testing The APP Sensor 1 Signal Circuit.

CASE 2: Your multimeter DID NOT register 10 to 12 Volts. Double check your connections and make sure you're testing the correct wire.

If your multimeter still does not register 10 to 12 Volts in this circuit, then you've found the cause of the APP Sensor 1 diagnostic trouble code (DTC). Repairing the cause of this missing Ground will get APP Sensor 1 back to work, since without Ground, APP Sensor 1 won't work.

Now, although it's beyond the scope of this tutorial to troubleshoot the problem with this Ground, but here are the two most like causes:

1. There's an 'open' on this wire between the APP Sensor Assembly's connector and the Throttle Actuator Control (TAC) Module.
2. The Throttle Actuator Control (TAC) Module is bad.