How To Test The Camshaft Position Sensor (1998-2001 3.9L V6 Dodge Ram Pickup)

TEST 2: Making Sure The CMP Sensor Has 5 Volts

If you're at this point, that means the CMP sensor didn't show any voltage switching between 5 and 0 Volts during TEST 1.

Most likely, the sensor isn't sending its ON/OFF signal because it's not getting power from the fuel injection computer (PCM).

So now we're gonna test if the violet with white stripe (VIO/WHT) wire is feeding 5 Volts DC to the CMP sensor.

If that checks out, we'll move on and confirm the sensor's also getting a good Ground.

Let's get started:

1. 1

   Disconnect the CMP sensor from its harness connector.

2. 2

   Place the black lead from your multimeter onto the battery's negative (-) terminal.

3. 3

   Set your multimeter to read DC Volts.

4. 4

   Turn the key to the ON position —but don't start or crank the engine.

5. 5

   Use the red multimeter lead to probe the terminal that connects to the VIO/WHT wire on the engine harness side.
   
   The VIO/WHT wire is the one that connects to the female terminal I've marked number 3 in the illustration above.
   
   NOTE: Make sure you're probing the connector with the female terminals —that's the one attached to the engine wiring harness.

6. 6

   You should see between 4.5 and 5 Volts on the meter.

Now here's what your results tell you:

CASE 1: You're seeing 4.5 to 5 Volts on the VIO/WHT wire. Perfect —that means the CMP sensor is getting power.

Next up, check if it's also getting a good Ground signal: TEST 3: Making Sure The CMP Sensor Has Ground.

CASE 2: You're NOT seeing 4.5 to 5 Volts on the VIO/WHT wire. Without that power, the CMP sensor can't generate a signal.

That usually means there's a break or open-circuit in the VIO/WHT wire between the sensor and the PCM.

Tracking down the cause of this missing voltage is beyond the scope of this tutorial, but your next step is to find the break and repair the wire.

TEST 3: Making Sure The CMP Sensor Has Ground

The camshaft position sensor also needs a strong Ground connection to send out that ON/OFF voltage signal.

In this final test, we're gonna check the black with light blue stripe (BLK/LT BLU) wire to confirm it's giving the CMP sensor a proper Ground.

IMPORTANT: The CMP sensor gets its Ground straight from the fuel injection computer (PCM). Don't connect the BLK/LT BLU wire to 12 Volts —doing that will toast the computer. The method I'm showing you here is safe and reliable for checking Ground with a multimeter.

Alright, here's what to do:

1. 1

   Unplug the CMP sensor from the connector.

2. 2

   Connect the red lead from your multimeter to the battery's positive (+) terminal.

3. 3

   Set your multimeter to measure DC Volts.

4. 4

   Turn the ignition key to the ON position —don't start or crank the engine.

5. 5

   Touch the black multimeter lead to the female terminal that connects to the BLK/LT BLU wire.
   
   The BLK/LT BLU wire is the one that connects to the female terminal I've marked number 2 in the illustration above.
   
   NOTE: Be sure you're testing the harness side —the connector with the female terminals coming from the engine wiring.

6. 6

   Your multimeter should show 10 to 12 Volts DC.

Here's how to read the results:

CASE 1: You're seeing 10 to 12 Volts on the meter. That confirms the sensor's getting the Ground it needs. You're good there.

The CMP sensor is bad and needs replacing if you've confirmed all of the following:

• Voltage didn't switch between 0 and 5 Volts in TEST 1.
• The VIO/WHT wire showed 5 Volts in TEST 2.
• The BLK/LT BLU wire delivered Ground in this test.

CASE 2: Your meter didn't show any voltage. That means there's no Ground, and the CMP sensor can't send its signal.

This usually means there's a break in the BLK/LT BLU wire somewhere between the connector and the PCM.

Tracking down that broken Ground wire is outside what we're covering here —but your next move is to find the issue and fix the wiring.

More 3.9L V6 Dodge Ram Pickup Diagnostic Tutorials

I've written quite a few 'how to' diagnostic tutorials for the V6 Dodge Ram pickup and you can find them in this index:

• 3.9L V6 Dodge Ram Pickup Index Of Articles.

Here's a small sample of the articles/tutorials you'll find in the index:

• How To Test The Intake Air Temp (IAT) Sensor (1998-2001 3.9L V6 Dodge Ram Pickup).
• How To Test The Fuel Pump (1992-2001 3.9L V6 Dodge Ram Pickup).
• How To Test The TPS (1997-2001 3.9L V6 Dodge Ram Pickup).
• How To Test For A Blown Head Gasket (1989-2001 3.9L V6 Dodge Ram Pickup).