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

Testing the camshaft position (CMP) sensor on your 1998–2001 3.9L V6 Dodge Ram pickup is easier than you think!

I'm gonna show you three quick tests you can do using a basic multimeter —no scan tool, no expensive gear— to figure out if the CMP sensor's doing its job or it's toast.

I'm also gonna point you to some solid replacement options that won't drain your wallet.

NOTE: The camshaft position sensor is also referred to as the distributor pickup coil.

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: 1998, 1999, 2000, 2001.
• 3.9L V6 Dodge Ram 2500 Pickup: 1998, 1999, 2000, 2001.

IGNITION SYSTEM WIRING DIAGRAMS:

• Ignition System Wiring Diagram (1998-2000 3.9L V6 Dodge Ram Pickup).
• Ignition System Wiring Diagram (2001 3.9L V6 Dodge Ram Pickup).

OTHER CMP SENSOR TESTS:

• How To Test The Distributor Pickup Coil (1989-1991 3.9L V6 Dodge Ram Pickup).
• How To Test The Camshaft Position Sensor (1992-1995 3.9L V6 Dodge Ram Pickup).
• How To Test The Camshaft Position Sensor (1996-1997 3.9L V6 Dodge Ram Pickup).

Symptoms Of A Bad CMP Sensor

When the CMP sensor goes bad, the PCM (Powertrain Control Module) usually throws one of these diagnostic trouble codes (DTCs):

• P0340: No Camshaft Signal Detected at PCM.
• P1391: Intermittent Loss of CMP or CKP Signal.

But codes aren't the only sign something's wrong. You'll likely notice a few of these other symptoms:

• Engine cranks but doesn't start: The engine turns over but won't fire up. That's because fuel injectors aren't firing correctly. Even if you've got spark at the plugs, the PCM can't sync the fuel timing.
• Random stalling: Sometimes the engine runs fine, then dies out of nowhere —usually while idling or at low RPMs.
• Check Engine Light (CEL): If the PCM sets a P0340 or P1391 DTC, that light on your dash is gonna come on.
• Rough idle or misfires: A weak or jumpy signal from the CMP sensor messes with fuel delivery. That can make the engine stumble, hesitate, or misfire at idle.
• Poor gas mileage: When injector timing is off, the engine burns more fuel than it needs. That hurts your MPG and can even cause black smoke from the tailpipe.
• Hard starting (hot or cold): If the CMP sensor signal is flaky but not completely gone, the engine might eventually start —but only after a few long cranks.
• Sluggish acceleration or hesitation: You may feel flat spots when you hit the gas or slow response when accelerating.

What the CMP Sensor Actually Does

On your 1998–2001 V6 Dodge Ram pickup, the camshaft position (CMP) sensor sits inside the distributor —it used to be called the pickup coil.

It works hand-in-hand with the crankshaft position (CKP) sensor, making sure fuel gets injected at the exact right time.

Here's what it's doing behind the scenes:

• Creates a Fuel Sync Signal:
  • When the engine's cranking or running, the CMP sensor sends out a signal called the fuel sync signal.
  • This tells the PCM which cylinder is in the compression stroke.
  • If the PCM doesn't get this signal, it can't fire the injectors correctly.
• Teams up with the CKP sensor:
  • There's also a crankshaft position (CKP) sensor taking readings from the flywheel.
  • The CKP reports crankshaft position and engine speed only (no cylinder ID).
  • The CMP steps in and gives the PCM the info it needs to match up each crank turn to the correct cylinder.
• Keeps fuel injection in sync:
  • The CMP signal helps the PCM fire each fuel injector right when its cylinder needs it.
  • Without this timing, the engine won't run right —or at all.
• Helps with spark timing (indirectly):
  • While the crank sensor mainly handles spark timing, the CMP gives extra info about cylinder position that keeps things dialed in.

Circuit Descriptions Of The Camshaft Position Sensor

The camshaft position sensor needs both power and Ground to work and send out a signal. That's why you'll see three wires coming out of its connector.

The table below gives you a quick rundown of what each wire does:

Pin	Wire Color	Description
1	Tan with yellow stripe (TAN/YEL)	CMP Signal
2	Black with light blue stripe (BLK/LT BLU)	Sensor Ground
3	Violet with white stripe (VIO/WHT)	5 Volts DC

Where To Buy The Camshaft Position Sensor

The following links will help you comparison shop for the camshaft position sensor (distributor pickup coil). I think you'll save a few bucks:

TEST 1: Testing The Camshaft Position Signal

While the engine's cranking or running, the CMP sensor sends out a voltage signal that flips between ON and OFF. When it's ON, you'll see 5 Volts DC. When it's OFF, it drops to 0 Volts.

Here's the good news —you can catch that voltage flip using a regular multimeter. That's exactly how we're gonna test it.

If the camshaft position sensor fails, it usually stops switching and just stays stuck at one voltage the whole time the engine cranks.

So in our first test, we'll connect a multimeter to the CMP's signal wire and check if the voltage jumps back and forth between 5 and 0 Volts like it's supposed to.

The wire you're after is the tan wire with a yellow stripe (TAN/YEL) —that's the wire that carries the ON/OFF signal.

IMPORTANT: The sensor has to stay plugged into its engine harness connector during this test. You'll need to use a back probe or pierce the wire insulation to read the signal inside 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? This is the one I use: Tekpower TP8268 AC/DC Auto/Manual Range Digital Multimeter (at: amazon.com).

Here's how to run the test step by step:

1. 1

   Connect the black lead from your multimeter right on the battery's negative (-) terminal.

2. 2

   Unplug the ignition coil's electrical connector. This step's a safety precaution, it'll keep the engine from starting —don't skip it.
   
   NOTE: Leave the distributor cap on. It holds the camshaft position sensor in place, so it needs to stay where it is.

3. 3

   Set your multimeter to measure DC Volts.

4. 4

   Tap the red multimeter lead into the tan/yellow stripe (TAN/YEL) wire from the CMP sensor's connector.
   
   NOTE: The sensor needs to stay connected to the engine harness so the signal can be read properly.

5. 5

   With your leads in place, have someone crank the engine for a few seconds while you watch the reading.

6. 6

   If everything's working, you'll see the voltage jump back and forth between 5 Volts and 0 Volts DC while the engine's spinning.

Here's how to make sense of what you saw:

CASE 1: The voltage switches between 5 and 0 Volts. That's exactly what you want. The CMP sensor is doing its job. It's not the reason your V6 Dodge Ram pickup isn't starting.

CASE 2: Voltage stays stuck —it doesn't flip between 5 and 0 Volts. That usually means the CMP sensor's bad.

But before replacing it, make sure the sensor's getting both power and Ground. Go on to: TEST 2: Making Sure The CMP Sensor Has 5 Volts.