How To Test The Cam Sensor Diagnostic Trouble Codes: P0340, P0341

Testing the camshaft position sensor, inside the distributor on all 4.3L, 5.0L, and 5.7L GM equipped mini-vans, pick ups and SUVs, can be easily and accurately done with just a multimeter.

No scan tool required for the cam sensor test since a scan tool is not gonna' be much help. Also a resistance test of the cam sensor will get you no-where since the camshaft position sensor is a Hall Effect type sensor that can not be Ohm-ed (resistance tested) with a multimeter.

I'm gonna' show you a way to do it with just a multimeter (in Volts DC mode) that is so accurate that you'll be able to say, 'Yes, the camshaft position sensor is bad' or 'No, the camshaft position sensor is OK'. And as you know this is a time and money saver.

This article will also help you to troubleshoot the following diagnostic trouble codes: P0340 (Camshaft Position (CMP) Sensor Circuit) and P0341 (Camshaft Position (CMP) Sensor Performance).

If you need to know if this camshaft position sensor test applies to your specific 4.3L, 5.0L, 5.7L GM mini-van, pick up or SUV, take a look at the 'Applies To:' box on the right and scroll with the next button to see all of the applications.

You can find this tutorial in Spanish here: Cómo Probar El Sensor De La Posición Del Árbol De Levas (P0340, P0341) (at: autotecnico-online.com).

Tools Needed To Test The Cam Sensor

You don't need any expensive tools to test the camshaft position sensor on your 4.3L, 5.0L, 5.7L engine.

Tools You'll Need:

• Multimeter.
  • You can use a digital multimeter or an analog multimeter although the digital one is the preferred one.
  • If you don't have a multimeter or need to upgrade yours, check out my recommendation here: Buying A Digital Multimeter For Automotive Diagnostic Testing (at: easyautodiagnostics.com).
• 1/2 inch ratchet wrench
• Socket that will fit crankshaft pulley bolt.
• A helper.

Symptoms Of A Bad Cam Sensor

When the camshaft position sensor goes bad, it will NOT keep your 4.3L, 5.0L, or 5.7L GM equipped vehicle from starting. Yep, that's right your mini-van or pick up or SUV will crank up and start. Now, of course, it's not gonna' run right.

Here are a couple of symptoms that your vehicle is probably experiencing:

• The check engine light will be on and the following codes may be stored in the PCM's memory:
  • - P0340 Camshaft Position (CMP) Sensor Circuit.
  • - P0341 Camshaft Position (CMP) Sensor Performance.
• Your GM mini-van, pick up, or SUV gas mileage is going thru' the roof (in a negative manner-o'-speaking that is).
• Your GM mini-van, pick up or SUV idles rough.
• Hard start (starts after an extended amount of cranking time).

The very first thing you need to ask yourself, before testing the camshaft position sensor is: Did the codes (P0340, P0341) or the symptoms appear after I replaced or moved the distributor?.

If the answer is YES to the above question then you need to read the next section.

The Trouble Codes Appeared After Replacing The Distributor

In all of the years I've been working on cars (as an automotive tech), the number one cause of DTCs P0340 and/or P0341 has been that the distributor was removed and installed but not synchronized correctly.

If this is the case in your specific situation then you have found the solution to your problem (and diagnostic trouble codes).

You'll need to synchronize the timing marks on the distributor and the crankshaft pulley/ timing cover so that the rough idle, check engine light and trouble codes can go away.

You'll need to use a repair manual (or a Google Search) to find out how to install the distributor correctly since I don't cover any remove and replace info in this article.

If you haven't removed the distributor at all, then this article will help you since it sounds like the camshaft position sensor is defective and I'll show you how to test it.

Where To Buy The Cam Sensor And Save

You can buy the camshaft position sensor individually or if you need, you can buy the whole distributor. If you need to save some money I suggest buying it online below.

Below you can buy the OE cam sensor (AC Delco 213-920 mistakenly labeled as the crank sensor in the box below) or the entire distributor for a whole lot cheaper than at the auto parts store:

How The Cam (CMP) Sensor Works

The camshaft position (CMP) sensor is a three wire Hall Effect type sensor that needs power and Ground to produce a signal.

The cam sensor is located within the distributor assembly and as such, it's rotated by the camshaft. This also means that a cam signal is created and sent to the PCM once every two revolutions of the crankshaft.

Here, in a nutshell is what happens when you crank and start the engine:

1. Power is supplied to the camshaft position sensor in the form of 12 Volts (ignition/battery source).
2. Ground is provided internally by the Powertrain Control Module (PCM, which is the technical name for the fuel injection computer).
3. As the distributor rotor turns,
   • The vane (underneath and attached to the rotor) interrupts the Hall Effect sensor.
   • When this vane, on the reluctor wheel, crosses the cam sensor, the cam sensor produces one 12 Volt Pulse.
   • When the vane, on the reluctor wheel, completely passes the cam sensor, the 12 Volt pulse goes to 0 Volts.
4. This ON/OFF 12 Volt pulse will continue as long as the engine is turning.

The best way to test the camshaft position sensor is testing in action (such as the test I've written in this article). The cam sensor can not be tested by a simple multimeter resistance test.

CMP TEST 1: Testing The Camshaft Position Signal With A Multimeter

The cam sensor (camshaft position sensor) is located inside the distributor on your Chevy (or GMC or Isuzu or Olds or Cadillac) mini-van or pick up or SUV. And as I mentioned at the beginning of the article the cam sensor test is done with a multimeter in Volts DC mode.

So the very first thing you need to do, to start your cam sensor troubleshooting, is to verify that the camshaft position sensor is either producing a cam signal or not. I'm gonna' ask you to manually rotate the engine with a 1/2 inch ratchet and the appropriate socket on the crank pulley (which means you can not use the starter motor to crank the engine).

Manually turning the engine by hand is important because this is the only way that this test can be completely accurate. I also recommend that you read this entire article first, especially familiarize yourself with the working theory of the camshaft position sensor found in the subheading How The Cam (CMP) Sensor Works.

OK, here's the test:

1. 1

   Disable the fuel injectors by unplugging the large connector (located right behind the throttle body) that supplies the fuel injectors, inside the plenum, with power and their activation signal. This is important, since it will keep the fuel injectors from injecting fuel as you're manually turning the engine.

2. 2

   Disable the ignition system by disconnecting the ignition control module or the ignition coil from their electrical connector. This will keep the ignition system from creating and delivering spark to the spark plugs.

3. 3

   Locate the cam sensor's connector and remove some of the plastic wiring loom protector so that you can gain access to the three wires inside.

4. 4

   Using an appropriate tool, like a wire-piercing probe, pierce the wire identified by the letter B shown in the image above (this will be the middle wire of the connector).
   
   To see what a what wire piercing probe tool looks like, click here: Wire Piercing Probe.
   
   This wire (circuit) is the one that brings the cam signal to the Powertrain Control Module (PCM, or in layman's terms: Fuel Injection Computer).

5. 5

   Connect the black multimeter test lead to the battery negative (-) terminal.

6. 6

   Once your multimeter (and it's test leads) are set up, have a helper manually turn the engine using a 1/2 ratchet and the right socket on the crankshaft pulley as you keep your eyeballs on the multimeter.
   
   Do not use the starter motor to crank up the engine, since your multimeter will not produce the same accurate result as manually turning the engine by hand. Also, the cam sensor must be connected to its connector.

7. 7

   While your helper is turning the engine (manually), your multimeter should register an ON/OFF 12 Volt DC signal.
   
   To go into more detail: if the camshaft position sensor is working like it should, on your 4.3L (or 5.0L or 5.7) mini-van or pick up or SUV, your multimeter will register 0 Volts (which is the OFF signal) and when the camshaft position sensor is activated, the multimeter will register 12 Volts DC (and this is the ON signal). This ON/OFF process should continue the whole time the engine is being manually cranked.

Let's interpret your test results:

CASE 1: The multimeter registered the ON/OFF 12 Volt signal as the engine was manually turned. This is good, and let's you know that the cam sensor within the distributor is OK and not the cause of the cam sensor code lighting up the check engine on your instrument cluster.

I've had this happen to me before, where the cam sensor checks out good and what really was happening was that this wire (circuit labeled with the letter B) had an open-circuit problem and the cam signal was not reaching the PCM.

CASE 2: The multimeter DID NOT register the ON/OFF 12 Volt signal as the engine was manually turned. This means that the camshaft position sensor is not producing a cam signal that the PCM can use.

With this test result alone, you can't condemn the cam sensor just yet. Two more important things have to be checked and they are: 1.) That the camshaft position sensor is getting power and 2.) that it has a good Ground. The next test will help you to verify the power circuit, go to: CMP TEST 2: Making Sure The CMP Sensor Is Getting Power.