How To Test The Camshaft Position Sensor (2002, 2003, 2004, 2005 4.2L Chevrolet TrailBlazer And GMC Envoy)

In this tutorial I'm going to show you how to test the camshaft position sensor, on the 2002-2005 4.2L Chevrolet TrailBlazer and GMC Envoy, using a multimeter in Volts DC mode.

With your multimeter test results will be able to accurately diagnose the camshaft position sensor as defective or not.

En Español You can find this tutorial in Spanish here: Cómo Probar El Sensor De La Posición Del Árbol De Levas (2002-2005 4.2L Chevrolet Trailblazer) (at: autotecnico-online.com).

NOTE: You can find the ignition system wiring diagram here: Ignition System Wiring Diagram (2002-2005 4.2L Chevrolet TrailBlazer).

Tools Needed To Test The Cam Sensor

You don't need any expensive tools to test the camshaft position sensor on your 2002-2005 4.2L Chevrolet TrailBlazer or GMC Envoy.

Tools You'll Need:

  1. Multimeter.
    1. You can use a digital multimeter or an analog multimeter although the digital one is the preferred one.
    2. If you don't have a multimeter or need to upgrade yours, check out my recommendation here: Buying A Digital Multimeter For Automotive Diagnostic Testing (at: easyautodiagnostics.com).
  2. 1/2 inch ratchet wrench
  3. Socket that will fit crankshaft pulley bolt.
  4. A helper.

Symptoms Of A BAD Cam Sensor

The fuel injection computer on your 2002-2005 4.2 Chevrolet TrailBlazer or GMC Envoy uses the signal that the camshaft position sensor produces (in conjunction with the crankshaft position sensor signal) to:

  1. Control the camshaft actuator solenoid.
  2. Identify the compression stroke of each of the six cylinders.
  3. To control the sequential injection of fuel of the fuel injectors.

Since the camshaft position sensor is a critical component of the ignition system, when it fails the check engine light will illuminate with a camshaft position sensor trouble code. You'll see one of the following trouble codes:

  1. P0340 Camshaft Position (CMP) Sensor Circuit.
  2. P0341 Camshaft Position (CMP) Sensor Performance.

You're also gonna' see one or more of the following:

  1. Bad gas mileage.
  2. Rough engine idle.
  3. Hard start (starts after an extended amount of cranking time).

TEST 1: Testing The CMP Signal With A Multimeter

How To Test The Camshaft Position Sensor (2002, 2003, 2004, 2005 4.2L Chevrolet TrailBlazer And GMC Envoy)

The camshaft position sensor produces an ON/OFF voltage signal as the engine turns.

ON is when the signal output is 12 volts and OFF is when the signal outputs 0 volts.

We can easily check to see if the camshaft position sensor is producing this ON/OFF voltage signal by connecting a multimeter to the camshaft position sensor signal wire and then manually turning the engine.

The wire that we need to connect to is the one labeled with the letter B in the photo above. This wire is the brown with white stripe (BRN/WHT) wire of the connector.

It's important to turn the engine by hand, using a half inch ratchet and the appropriate socket on the crankshaft pulley, so that you can see this ON/OFF voltage signal on your multimeter.

NOTE: The camshaft position sensor must remain connected to its electrical connector for this test to work. To access the voltage signal within the wire you'll need to use a back-probe or a wire piercing probe. You can see an example of this tool here: Wire Piercing Probe.

These are the test steps:

  1. 1

    Disable the ignition system by disconnecting all 6 ignition coils from their electrical connectors.

    This step is important!

  2. 2

    Locate the cam sensor's connector and remove some of the plastic wiring loom protector so that you can gain access to the three wires inside.

  3. 3

    Connect the red multimeter test lead to the wire identified by the letter B in the photo above.

  4. 4

    Connect the black multimeter test lead to the battery negative (-) terminal.

  5. 5

    Turn the key ON but don't crank the engine.

  6. 6

    Manually turn the engine using a 1/2 ratchet and the right socket on the crankshaft pulley.

    NOTE: Don't use the starter motor to turn the engine, since your multimeter will not produce the same accurate result as manually turning the engine by hand.

  7. 7

    The multimeter should register an ON/OFF 12 Volt DC.

    To go into more detail: If the camshaft position sensor is OK, your multimeter will register a reading that changes between 0 Volts and 12 Volts DC as you manually turn the engine.

Let's interpret your test results:

CASE 1: The multimeter registered the ON/OFF voltage signal as the engine was manually turned. This is the correct and expected test result and lets you know that the camshaft position sensor is working correctly.

This test result also lets you know that the camshaft position sensor is getting both power and Ground from your TrailBlazer or Envoy's fuel injection computer.

CASE 2: The multimeter DID NOT register the ON/OFF 12 voltage signal as the engine was manually turned. This means that the camshaft position sensor is not producing a cam signal that the PCM can use.

With this test result alone, you can't condemn the camshaft position sensor just yet. Two more important things have to be checked and they are: 1.) that the camshaft position sensor is getting power and 2.) that it's getting Ground. The next test will help you to verify the power circuit, go to: TEST 2: Making Sure The Camshaft Position Sensor Is Getting Power.