How To Test The Camshaft Position Sensor (1998-2003 5.2L, 5.9L V8 Dodge Ram Van)

If the PCM's throwing a P0340 or P1391 trouble code and your engine won't start, you've come to right place to figure it out.

This tutorial walks you through three fast and simple tests you can run on the CMP sensor to see if it's working or fried.

You'll only need a basic multimeter —no scan tool, no fancy gear.

If you're just looking to swap it out, I'll also show you a few solid replacement choices that won't wreck your budget.

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

APPLIES TO: This tutorial applies to the following vehicles since they use the exact same camshaft position (CMP) sensor:

• Dodge Ram 1500 Van 5.2L V8: 1998, 1999, 2000, 2001, 2002, 2003.
• Dodge Ram 2500 Van 5.2L V8: 1998, 1999, 2000, 2001, 2002, 2003.
• Dodge Ram 3500 Van 5.2L V8: 1998, 1999, 2000, 2001, 2002, 2003.
• Dodge Ram 1500 Van 5.9L V8: 1998, 1999, 2000, 2001, 2002, 2003.
• Dodge Ram 2500 Van 5.9L V8: 1998, 1999, 2000, 2001, 2002, 2003.
• Dodge Ram 3500 Van 5.9L V8: 1998, 1999, 2000, 2001, 2002, 2003.

IGNITION SYSTEM WIRING DIAGRAMS:

• Ignition System Wiring Diagram (1998-1999 5.2L, 5.9L Dodge Ram Van).

OTHER CMP SENSOR TESTS:

• How To Test The Distributor Pickup Coil (1989-1991 5.2L, 5.9L V8 Dodge Ram Van).
• How To Test The Camshaft Position Sensor (1992-1995 5.2L, 5.9L V8 Dodge Ram Van).
• How To Test The Camshaft Position Sensor (1996-1997 5.2L, 5.9L V8 Dodge Ram Van).

Symptoms Of A Bad CMP Sensor

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

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

But codes aren't the only clue. You'll probably see some of these other signs too:

• Engine cranks but won't start: The motor turns over but doesn't fire up.
• Random stalling: It might run smooth for a while, then shut off with no warning —usually when you're idling or cruising slow.
• Check Engine Light (CEL): When the PCM logs P0340 or P1391, the CEL on your dash is gonna light up.
• Misfires or rough idle: A weak CMP signal throws fuel delivery out of sync. That makes the engine stumble, hesitate, or misfire, especially at idle.
• Hard to start —hot or cold: If the signal's weak but still there (or glitchy), the engine might eventually start after a few long cranks.
• Hesitation or sluggish response: You might feel a delay or flat spot when stepping on the gas.

What the CMP Sensor Does

On a 1998–2003 V8 Dodge Ram van, the CMP sensor is inside the distributor. It works together with the crankshaft position (CKP) sensor to make sure fuel injection and spark are timed just right.

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

• Sends a Fuel Sync Signal:
  • When the engine's turning —starting or running — the CMP fires off a signal called the fuel sync signal.
  • This tells the PCM which cylinder's in the compression stroke so it can time the injectors correctly.
• Works with the CKP sensor:
  • The CKP sensor reads from the flywheel and tells the PCM engine speed and crankshaft position.
  • But it doesn't know cylinder order. The CMP fills in that info so the PCM can sync everything.
• Keeps injector timing on point:
  • The PCM uses the CMP signal to fire injectors at the right time.
  • No signal? Fuel delivery's off —or doesn't happen at all.
• Supports spark timing (indirectly):
  • The CKP handles spark timing, but the CMP helps confirm which cylinder's up next.

Circuit Descriptions Of The Camshaft Position Sensor

Since the camshaft position sensor is a 3-wire Hall-Effect type, it needs both power and Ground to do its job and send out a signal.

Here's a quick breakdown of what each wire does in the table below:

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, it puts out 5 Volts DC. When it's OFF, it drops to 0 Volts.

Here's the cool part —you can catch that voltage flip using a regular multimeter. That's exactly how we're gonna test it in this section.

When the sensor goes bad, it usually quits switching and just stays stuck at one voltage the whole time the engine's cranking.

The wire we need to tap into (to check the signal voltage) is the tan with yellow stripe (TAN/YEL) wire.

IMPORTANT: Leave the sensor plugged into its engine wiring harness connector while testing. You'll need to back probe the connector or pierce the wire insulation to read the signal inside. You can see an example of a wire piercing probe (and where to buy it) 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 what you're gonna do:

1. 1

   Attach the black multimeter lead to the battery's negative (-) terminal.

2. 2

   Unplug the ignition coil connector. This keeps the engine from firing up while you're testing —don't skip it.
   
   NOTE: Leave the distributor cap on. It holds the CMP sensor in place, so it needs to stay put.

3. 3

   Set your multimeter to read DC Volts.

4. 4

   Tap the red lead into the tan with yellow stripe (TAN/YEL) wire coming out of the CMP sensor connector.
   
   NOTE: Don't unplug the sensor. It has to stay connected to the harness for the signal to show up right.

5. 5

   With the leads in place, have someone crank the engine for a few seconds while you keep an eye on the multimeter.

6. 6

   If everything's good, the voltage will bounce between 5 Volts and 0 Volts DC while the engine turns.

Here's how to read the results:

CASE 1: Voltage jumps between 5 and 0 Volts. That's what you want. The CMP sensor's working like it should. It's not the cause of your engine's no-start problem.

CASE 2: Voltage stays flat —no switching. That usually means the CMP sensor's shot.

But don't replace it just yet. First, make sure it's actually getting power and Ground. Go to: TEST 2: Making Sure The CMP Sensor Has 5 Volts.