If you suspect that the camshaft position (CMP) sensor, on your 1996-1997 3.9L Dodge Ram pickup, is bad and causing a no-start problem or a trouble code P0340, then this is the tutorial you need to test it.
The cool thing is that the camshaft position sensor can be diagnosed as good or bad in 3 tests and they're not difficult to perform.
In this tutorial I'll explain these 3 tests in a step-by-step manner so that you can find out if the CMP sensor is bad (or not).
NOTE: The camshaft position sensor is also known as the distributor pickup coil.
Contents of this tutorial:
- Symptoms Of A Bad Camshaft Position (CMP) Sensor.
- Circuit Descriptions Of The Camshaft Position Sensor.
- Where To Buy The Camshaft Position Sensor.
- TEST 1: Testing The Camshaft Position Signal.
- TEST 2: Making Sure The CMP Sensor Has 5 Volts.
- TEST 3: Making Sure The CMP Sensor Has Ground.
- More 3.9L V6 Dodge Tutorials.
You can find this tutorial in Spanish here: Cómo Probar El Sensor CMP (1996-1997 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 1500 Pickup: 1996, 1997.
WIRING DIAGRAM: You can find the ignition system wiring diagram here:
Symptoms Of A Bad Camshaft Position (CMP) Sensor
Your 3.9L Dodge Ram pickup's fuel injection computer is the component that activates the fuel injectors and the ignition coil to get the engine started.
The two main signals that the computer uses to activate them is the camshaft position (CMP) sensor signal and the crankshaft position (CKP) signal.
Since the computer constantly monitors the CMP signal (as the engine cranks and runs), when the CMP sensor fails you'll see the following trouble code stored in its memory:
- P0340: No Camshaft Signal At PCM.
Circuit Descriptions Of The Camshaft Position Sensor
As you can see in the photo above, the camshaft position sensor is a 3-wire ignition system component. Two of these wires feed 5 Volts and Ground to the sensor (without power and Ground the sensor will not create its signal).
In the table below is a brief description of each of the 3 wires:
|1996-1997 Camshaft Position Sensor Connector|
|1||Violet with white stripe (VIO/WHT)||5 Volts DC|
|2||Black with light blue stripe (BLK/LT BLU)||Sensor Ground|
|3||Tan with yellow stripe (TAN/YEL)||CMP Signal|
An ignition system wiring diagram, for the 1996-1997 3.9L V6 Dodge Ram 1500 pickup can be found here:
When testing the CMP sensor, it's important to knowt that it creates an ON/OFF voltage signal as the engine turns. ON is when the CMP signal is at 5 Volts DC. OFF is when the CMP signal is at 0 Volts.
The cool thing is that we can see this ON/OFF voltage switching between 5 Volts and 0 Volts with a multimeter, and this is how we're gonna' test it.
Where To Buy The Camshaft Position Sensor
The camshaft position sensor (which is also called the distributor pick-up coil) is located in the distributor. It's no an expensive component and it can be found in any auto parts store, but I think you'll save a few bucks by buying it online. Check out the following links and compare:
TEST 1: Testing The Camshaft Position Signal
Generally, the camshaft position sensor will stay stuck producing a single voltage value as the engine turns when it has failed.
Thankfully, checking to see if the sensor's signal voltage is switching between 5 Volts and 0 Volts is not difficult.
In this first test section we're gonna' tap into the tan with yellow stripe (TAN/YEL) wire, which is labeled with the number 3 in the photo above, with our multimeter.
If the sensor is working correctly, you should see the CMP signal switching between 5 Volts and 0 Volts as your helper cranks the engine.
IMPORTANT: The camshaft position sensor must remain 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.
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:
Place your multimeter in Volts DC mode.
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.
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.
Connect the black multimeter test lead directly on the battery negative (-) terminal.
Have your helper crank the engine for a few seconds once the multimeter test lead connections are set up.
Your multimeter should see the voltage switch between 5 Volts and 0 Volts DC as the engine is cranking.
Let's examine your test result:
CASE 1: The ON/OFF voltage signal is present. This is the correct and expected test result.
Since the CMP voltage signal is switching between 5 Volts and 0 Volts, you can conclude that the CMP sensor is good and that it IS NOT behind the no-start problem.
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, we need to make sure that it's getting 5 Volts on the violet with white stripe (VIO/WHT) wire. For this test go to: TEST 2: Making Sure The CMP Sensor Has 5 Volts.