Testing the camshaft position sensor, which is located inside the distributor, is not difficult at all.
The cool thing is that you don't need any expensive diagnostic equipment to do it, since it can be tested with a simple multimeter.
In this tutorial I'll explain the 3 tests that you need to perform to find out if it's good or bad.
NOTE: The camshaft position sensor is also known as the distributor pickup coil.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar El Sensor CMP (1992-1995 3.9L Dodge Ram Pickup) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles since they use the exact same camshaft position (CMP) sensor:
- 3.9L V6 Dodge Ram D150 Pickup: 1992, 1993.
- 3.9L V6 Dodge Ram D250 Pickup: 1992, 1993.
- 3.9L V6 Dodge Ram W150 Pickup: 1992, 1993.
- 3.9L V6 Dodge Ram 1500 Pickup: 1994, 1995.
WIRING DIAGRAM: You can find the ignition system wiring diagrams here:
- Ignition System Wiring Diagram (1992-1993 3.9L V6 Dodge Pickup And Van).
- Ignition System Wiring Diagram (1994-1995 3.9L V6 Dodge Ram 1500 And 2500 Pickups).
Symptoms Of A Bad Camshaft Position (CMP) Sensor
The camshaft position sensor is a critical component of your 3.9L V6 Dodge Ram pickup or van's ignition system.
This is due to the fact that the fuel injection computer needs the camshaft position (CMP) sensor signal and the crankshaft position (CKP) sensor signal to start injecting fuel and activating the ignition coil for the engine to start.
If the CMP signal is missing, the engine is not going to start due to a lack of fuel or spark.
The fuel injection computer is programmed to set a trouble code when the CMP sensor fails (but doesn't always do so). When it does set a trouble code, you'll see the following trouble code stored in the computer's memory:
- Code 54: No Cam Sync Signal Detected.
Circuit Descriptions Of The Camshaft Position Sensor
As you can see in the photo above, the camshaft position sensor has 3 wires coming out of its electrical connector.
In the table below you'll find a short description of each of the 3 wires:
| 1992-1995 Camshaft Position Sensor Connector | ||
|---|---|---|
| Pin | Wire Color | Description |
| 1 | Orange (ORG) | 8 Volts DC |
| 2 | Black with light blue stripe (BLK/LT BLU) | Sensor Ground |
| 3 | Tan with yellow stripe (TAN/YEL) | CMP Signal |
The following ignition system wiring diagrams will further help you identify the camshaft position sensor circuits:
- Ignition System Wiring Diagram (1992-1993 3.9L V6 Dodge Pickup And Van).
- Ignition System Wiring Diagram (1994-1995 3.9L V6 Dodge Ram 1500 And 2500 Pickups).
In a nutshell, as the engine turns (either because it's cranking or running) the camshaft position sensor creates an ON/OFF voltage signal. ON is when the CMP signal is at 5 Volts DC. OFF is when the CMP signal is at 0 Volts.
This ON/OFF voltage can be observed easiy with a multimeter in Volts DC mode, and this is how we're gonna' test it.
Where To Buy The Camshaft Position Sensor
The following links will help you comparison shop for the camshaft position sensor (distributor pick-up coil). I think you'll save a few bucks:
TEST 1: Testing The Camshaft Position Signal
The very first thing that we're going to do is to make sure that the camshaft position sensor is creating and ON/OFF voltage signal when the engine is cranking.
For the most part, when the CMP sensor fails it will stay stuck producing a single voltage value as you crank the engine.
To be a bit more specific, you're not going to see the ON/OFF voltage signal on your multimeter when you crank the engine.
If your test result confirms that the camshaft position sensor is not producing its signal, then the next step is to make sure that it's getting 8 Volts.
IMPORTANT: The camshaft position sensor must be connected to its engine harness connector for this test to work. You'll need to use a back probe or a wire piercing probe to read the CMP voltage signal within the wire. You can see an example of a wire piercing probe here: Wire Piercing Probe Review (Power Probe PWPPPPP01).
NOTE: Don't have a multimeter or need to upgrade yours? Check out my recommendation: Buying A Digital Multimeter For Automotive Diagnostic Testing (at: easyautodiagnostics.com).
These are the test steps:
- 1
Place your multimeter in Volts DC mode.
- 2
Disconnect the ignition coil from its electrical connector. This is an important safety precaution!
NOTE: Don't remove the distributor cap from the distributor. The distributor cap must be in place to hold down the camshaft position sensor. - 3
With the red multimeter test lead, probe the tan with yellow stripe (TAN/YEL) wire of the cam sensor connector.
NOTE: The camshaft position sensor must remain connected to its engine wiring harness connector to be able to read its signal. - 4
Connect the black multimeter test lead directly on the battery negative (-) terminal.
- 5
Have your helper crank the engine for a few seconds once the multimeter test lead connections are set up.
- 6
Your multimeter should see the voltage switch between 5 Volts and 0 Volts DC as the engine is cranking.
Let's examine your CMP signal test result:
CASE 1: The CMP sensor is producing an ON/OFF voltage signal. This is the correct and expected test result. You can conclude that the camshaft position sensor is functioning correctly and IS NOT behind the problem causing the engine to not start.
CASE 2: The multimeter DID NOT read the indicated ON/OFF DC voltage. This test result usually means that the camshaft position sensor is defective.
Before you replace it, make sure it's getting power and Ground. For the next test go to: TEST 2: Making Sure The CMP Sensor Has 8 Volts.