How To Test The Camshaft Position Sensor (1998-2003 3.9L V6 Dodge Ram Van)

TEST 2: Making Sure The CMP Sensor Has 5 Volts

In TEST 1, you saw the CMP sensor's voltage wasn't flipping between 5 and 0 Volts while cranking the engine.

One common reason for this is that the sensor isn't getting power —delivered by the violet with white stripe (VIO/WHT) wire— from the PCM.

So now, we're gonna check if the VIO/WHT wire is feeding 5 Volts DC to the CMP sensor.

If that checks out, we'll move on to TEST 3 and make sure the sensor's also getting a solid Ground.

Here's what to do:

1. 1

   Unplug the CMP sensor from the harness.

2. 2

   Touch the black multimeter lead to the battery's negative (-) post.

3. 3

   Set your multimeter to DC Volts.

4. 4

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

5. 5

   Touch the red lead to terminal 3 of the engine wiring harness connector. See the connector diagram above to ID the terminal.
   
   It's important that you verify the terminal corresponds to the VIO/WHT wire.
   
   NOTE: You're probing the connector with the female terminals.

6. 6

   Your multimeter should show between 4.5 and 5 Volts.

Here's how to read the results:

CASE 1: You're getting 4.5 to 5 Volts on the VIO/WHT wire. That's what we want. The CMP sensor is getting the power it needs.

Next step: Make sure it's receiving Ground —go to TEST 3: Making Sure The CMP Sensor Has Ground.

CASE 2: You're not getting 4.5 to 5 Volts on the VIO/WHT wire. No voltage means no signal —the sensor can't do anything without power.

This usually means there's a break in the VIO/WHT wire somewhere between the PCM and the sensor.

Tracking down and fixing this missing voltage is outside the scope of this guide. Your next move is to trace the wire and restore these 5 Volts to the circuit.

TEST 3: Making Sure The CMP Sensor Has Ground

Alright, if you've made it this far, you've already nailed down:

• TEST 1: The CMP sensor's voltage didn't flip between 0 and 5 Volts during cranking.
• TEST 2: The VIO/WHT wire is delivering 5 Volts to the sensor.

Now for the last check —we're gonna see if the black with light blue stripe (BLK/LT BLU) wire is giving the CMP sensor a solid Ground connection.

For that ON/OFF signal to reach the PCM, the sensor needs both power and Ground. No Ground, no signal.

IMPORTANT: This Ground comes straight from the PCM. Don't hook the BLK/LT BLU wire up directly to 12 Volts —you'll fry the computer. The steps below are a safe way to test for Ground using your multimeter without risk to the PCM.

Here's what to do:

1. 1

   Unplug the CMP sensor from its connector.

2. 2

   Touch the red multimeter lead to the battery's positive (+) post.

3. 3

   Set your multimeter to DC Volts.

4. 4

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

5. 5

   Touch the black lead to terminal 2 of the engine wiring harness connector. See the connector diagram above to ID the terminal.
   
   It's important that you verify the terminal corresponds to the BLK/LT BLU wire.
   
   NOTE: You're probing the connector with the female terminals.

6. 6

   You should see between 10 and 12 Volts on your multimeter.

Let's take a look at what your test result means:

CASE 1: You see 10 to 12 Volts. That's the confirmation we need —the sensor's got a good Ground.

If you've seen all three of these:

• No voltage switching in TEST 1.
• 5 Volts on the VIO/WHT wire in TEST 2.
• And now 10–12 Volts confirming Ground on the BLK/LT BLU wire —

Then the CMP sensor is toast. Go ahead and replace it.

CASE 2: No voltage on the meter. That means the sensor has no Ground, so it can't send out a signal.

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

Tracking down the cause of this missing Ground is beyond what this guide covers —but your next move is to troubleshoot and fix this issue.

More 3.9L V6 Dodge Ram Van Diagnostic Tutorials

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

• 3.9L V6 Dodge Ram Van Index Of Articles.

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

• How To Test The MAP Sensor (1997-2003 3.9L V6 Dodge Ram Van).
• How To Test The TPS (1997-2003 3.9L V6 Dodge Ram Van).
• How To Test The Fuel Pump (1992-2003 3.9L V6 Dodge Ram Van).
• Testing The Front Oxygen Sensor's Performance (1996-2003 3.9L V6 Dodge Ram Van).