P0340 Diagnostic: CMP Sensor Circuit Tests (1996-2003 5.2L, 5.9L V8 Dodge Ram Pickup)

TEST 3: Checking The CMP Sensor Wires For A Short To Ground

In this test, we're going to check each of the three CMP sensor wires for a short to Ground. None of these wires should show continuity to Ground —they should be completely electrically isolated unless the sensor or PCM is actively driving the circuit (which we've ruled out by disconnecting everything).

A short to Ground can happen when a wire's insulation wears through and makes contact with the engine block, a bracket, or some other metal surface. Even a slight rub-through can cause the PCM to misread the CMP signal and trigger a P0340 code.

We'll also do a wiggle test during this procedure to check for an intermittent short —so you'll need a helper to gently move the wiring harness between the CMP sensor and the PCM while you monitor the multimeter reading.

IMPORTANT: Be sure the battery negative (-) cable is disconnected from the battery post and all 3 PCM connectors from the PCM.

OK, let's get this show on the road:

1. 1

   Disconnect the battery's negative (-) cable from the battery post.

2. 2

   Disconnect all three PCM connectors from the PCM.

3. 3

   Disconnect the CMP sensor connector.

4. 4

   Set your multimeter to the Ohms (Ω) setting.
   
   NOTE: Don't use the Continuity setting on your multimeter.

5. 5

   Place one lead of the multimeter on a known good Ground point —preferably on the metal terminal of the battery's negative (-) cable (that is now disconnected from the battery).

6. 6

   With the other lead, probe the TAN/YEL wire terminal at the CMP sensor connector. You should see no continuity (infinite resistance).

7. 7

   Repeat this step for the BLK/LT BLU and VIO/WHT wires, one at a time. Each wire should be tested individually against Ground.

8. 8

   Have a helper gently wiggle the engine harness between the CMP sensor and the PCM while you monitor the reading for each wire.
   
   If the reading suddenly drops or glitches out, that wire is intermittently shorting to Ground.

Let's interpret your test results:

CASE 1: One or more wires show continuity to Ground (low resistance -usually under 5 Ohms). This confirms a short to Ground somewhere along the wire —most likely from damaged insulation contacting metal.

You'll need to find and repair the damaged section. See:

• How To Repair A Shorted Or Open Wire (Without Tearing Into The Entire Wiring Harness).

Take a look at this important section too:

• Watch Out For Shared Sensor Power And Ground Circuits.

CASE 2: None of the wires show continuity to Ground. That's exactly what we want —the CMP sensor circuits are properly isolated from Ground.

But before we celebrate, let's just be thorough. We now need to make sure none of the CMP wires are shorted to each other. Go to: TEST 4: Check If CMP Sensor Wires Are Shorted To Each Other.

TEST 4: Check If CMP Sensor Wires Are Shorted To Each Other

In this final wiring test, we're going to check that none of the three CMP sensor wires are shorted together. Each wire —the signal, Ground, and 5 Volt supply— should be electrically independent from the others.

If two wires are touching inside the harness due to melted insulation, pinched wiring, or corrosion, the PCM won't be able to properly detect the cam signal. This kind of internal short can definitely cause a P0340 and prevent the engine from starting.

Like the previous tests, this one requires that the PCM and CMP sensor connectors are unplugged. We'll test each combination of wires for continuity and also perform a wiggle test to catch any intermittent shorts caused by movement or vibration.

IMPORTANT: Make sure the battery negative (-) cable is still disconnected from the battery post and that all three PCM connectors are unplugged. We're testing the harness only —no voltage should be present.

NOTE: We're not going to test between the VIO/WHT (5 Volt supply) and BLK/LT BLU (Ground) wires. These two wires are shared by several other sensors that remain connected, so you'll see some level of continuity even if the circuit is perfectly fine.

Let's begin:

1. 1

   Ensure the battery negative (-) cable is disconnected and all three PCM connectors are unplugged.

2. 2

   Disconnect the CMP sensor connector if it's not already unplugged.

3. 3

   Set your multimeter to the Ohms (Ω) setting.
   
   NOTE: Don't use the Continuity setting of your multimeter.

4. 4

   Test for continuity between the TAN/YEL and BLK/LT BLU wires at the CMP sensor connector.
   
   There should be no continuity in the circuit (reading should be infinite or OL).

5. 5

   Test between the TAN/YEL and VIO/WHT wires.
   
   There should be no continuity in the circuit (reading should be infinite or OL).

6. 6

   Have a helper gently wiggle the engine wiring harness between the CMP sensor and the PCM while monitoring the readings for the two tests.
   
   There should be no fluctuation or continuity at any point.

Let's interpret your test results:

CASE 1: Continuity exists between two wires. This confirms a short in the CMP sensor's wiring —likely due to melted or chafed insulation inside the engine wiring harness.

You'll need to repair the shorted wires to solve the engine no-start and P0340 issue. See:

• How To Repair A Shorted Or Open Wire (Without Tearing Into The Entire Wiring Harness).

CASE 2: No continuity between any of the wires. Excellent —this confirms that none of the CMP sensor wires are shorted to each other.

But if the engine still isn't starting and the P0340 code keeps coming back, we're now facing a bit of a dilemma. At this point, you've already replaced the CMP sensor and verified that the wiring is OK —no open circuits, no shorts to Ground, and no internal wire-to-wire shorts.

That leaves us with two likely possibilities:

• A different sensor that shares the 5 Volt or Ground circuit has an internal short that's affecting the CMP circuit.
• The PCM itself may be failing to recognize the CMP signal due to an internal fault.

Make sure to check out these two important sections before moving forward:

• Watch Out For Shared Sensor Power And Ground Circuits.
• Is The PCM Bad?

Watch Out For Shared Sensor Power And Ground Circuits

Here's something a lot of folks overlook when chasing down a P0340 code: Both its Ground wire (BLK/LT BLU) and 5 Volt reference wire (VIO/WHT) are shared with several other sensors on the engine and transmission.

Depending on the year of your Dodge Ram (1996–2003), these circuits may also power the TPS, MAP, IAT, CKP, and even some transmission sensors —it varies by model and engine setup.

In my experience, it's not uncommon for one of these other sensors —not related to the cam sensor at all— to short out internally.

When that happens, it can pull down the shared Ground or the shared 5 Volt circuit, affecting every sensor connected to it. That includes the CMP sensor, and the PCM may never see its signal —even if the wiring and the sensor itself are perfectly fine.

Here's what you need to do: disconnect all of the sensors that share the CMP sensor's Ground and 5 Volt circuits. Then, with everything disconnected, repeat your continuity and short-to-Ground tests on all three CMP sensor wires (see TESTS 2 and 3). If the wires now test good, you've just proven that one of those other sensors is the culprit.

This kind of fault can be sneaky —everything looks fine at the CMP sensor connector, but in reality, a completely different sensor is dragging down the entire circuit.

The PCM doesn't know which sensor is to blame —it just knows the cam signal is missing, so it sets P0340. Don't skip this step if everything else has checked out but the problem still persists.

Is The PCM Bad?

It's easy to jump to the conclusion that the PCM (Powertrain Control Module) is bad —especially after replacing the CMP sensor and confirming that the wiring looks good. But in reality, PCM failure is extremely rare.

From what I've seen in the real world, one of the most common reasons a PCM gets fried is when someone tries to jump-start another vehicle and connects the jumper cables backward. That mistake sends a voltage spike through the system, and the PCM usually doesn't survive it.

That said, even without a voltage surge, a PCM can still fail on its own over time. These computers generate a lot of heat internally, and they're mounted in the engine bay —right where all the heat from the engine builds up. So sooner or later, internal circuits can wear out. But again, it's not something that happens often.

Here's the thing to keep in mind before pointing the finger at the PCM, there's a list of things that must be ruled out first. If any one of these hasn't been checked, it's way too early to blame the computer.

You must confirm the following:

• The CMP sensor has been replaced with a known-good one.
• The distributor shaft rotates when cranking and has no side-to-side play (TEST 1).
• The 5 Volt reference, Ground, and CMP signal wires show continuity between the CMP and PCM (TEST 2).
• No shorts to Ground exist on any of the CMP sensor wires (TEST 3).
• The CMP wires are not shorted to each other (TEST 4).
• All connectors (CMP and PCM) are clean, tight, and free of corrosion or damage.
• All sensors that share the CMP's Ground or 5 Volt circuit have been disconnected and ruled out as possible causes —one faulty sensor on a shared circuit can pull the whole line down and prevent the CMP signal from reaching the PCM.

If you've tested All of the above and everything checks out, but you're still stuck with a P0340 code and a no-start condition, then —and only then— it's time to consider the possibility of a bad PCM.

Also, don't be afraid to get a second opinion. If you can, have an experienced technician double-check your findings. When you do, make sure to give them a detailed list of everything you've already tested and what the results were. This helps them give you a better diagnosis based on facts —not guesswork.

Now, if you're thinking about trying an used PCM from a salvage yard, there are a few things to keep in mind:

• The replacement PCM must match: Year, engine size, and transmission type. Otherwise, it may not run the engine properly —or at all.
• It will need to be flashed with your vehicle's VIN and correct software to run correctly. Without flashing, even if the engine starts, the programming might be wrong and cause drivability issues.

Swapping in a matching used PCM can help you confirm whether the original PCM is the problem. If the engine starts and P0340 stays gone —awesome, the original PCM is bad. But remember —you'll still need to flash it with your truck's VIN to make it a permanent fix.

So don't be too quick to suspect the PCM. Make it your last step —not your first one.

More 5.2L, 5.9L V8 Dodge Ram Pickup Tutorials

I've written several more tutorials for the V8 Dodge Ram pickups that may be of interest to you that you can find in this index:

• 5.2L, 5.9L V8 Dodge Ram Pickup Index Of Articles.

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

• How To Test The Fuel Pump (1992-2003 5.2L, 5.9L V8 Dodge Ram Pickup).
• How To Test The MAP Sensor -P0107, P0108 (1997-2003 5.2L, 5.9L V8 Dodge Ram Pickup).
• How To Test Engine Compression (1989-2003 5.2L, 5.9L V8 Dodge Ram Pickup).
• Troubleshooting A Blown Head Gasket (1989-2003 5.2L, 5.9L V8 Dodge Ram Pickup).