How To Test The Crank Sensor (GM 4.3L, 5.0L, 5.7L)

This article will help you to troubleshoot and diagnose a bad crankshaft position sensor on your 4.3L, 5.0L and 5.7L Vortec equipped GM Pick Up or SUV.

Since the 3-wire crankshaft position (CKP) sensor can not be tested by a multimeter resistance test (Ohms), I've written this article to show you how to do it with just a multimeter in Volts DC mode. This is a very accurate and effective test and will help you to know if it's good or bad.

Since this crankshaft position sensor test article covers quite a few GM years, makes and models, take a look at the 'Applies To:' box on the right and scroll with the 'Next > >' button to see all of the applications. Also, the info in this article is geared towards diagnosing and troubleshooting a cranks but does not start or a no-start no-spark condition.

You can find this tutorial in Spanish here: Cómo Probar El Sensor De La Posición Del Cigüeñal (P0336, P0337, P0338, P0339) (at: autotecnico-online.com).

Important Suggestions

SUGGESTION 1: The crank sensor test I'm gonna' show you in this article, is one of the most accurate ways to test the crank sensor without an oscilloscope (and using only a multimeter) only if you turn the engine by hand. You'll need to use a 1/2 ratchet wrench and the appropriate socket to turn the crankshaft pulley.

SUGGESTION 2: It's very important that the Spider's fuel injector's connector be disconnected while performing the crankshaft position sensor test. Unplugging this connector will disable the computer from injecting fuel into the engine.

Tools Needed To Test The Crankshaft Position Sensor

You don't need any expensive tools to test the crank 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 Crankshaft Position Sensor

The most common symptom of a bad crank sensor is a 'cranks but does not start' problem. In other words, your GM vehicle will crank over when you turn the key to the Start position but will not start. Below is a simple list of more specific symptoms that accompany a bad crank sensor:

1. The ignition system will not produce spark:
   • The ignition coil will not spark.
   • No spark from all of the spark plug wires.
   • The ignition control module will not receive a triggering signal and without this triggering signal, the module will not switch the ignition coil ON and OFF to produce spark.
2. The PCM (Powertrain Control Module=fuel injection computer) will not pulse the fuel injectors.
3. The PCM will not activate the fuel pump after the initial priming voltage that the PCM sends to it when you turn the key to the ON position and then to the Start position.
4. The PCM will usually NOT set a specific bad crankshaft position sensor diagnostic trouble code (DTC) when the crank sensor goes rogue (goes bad). But, every now and then it does, and when it does you'll get:
   • P0336 CKP Sensor Circuit Performance.
   • P0337 CKP Sensor Circuit Low Frequency Code.
   • P0338 CKP Sensor Circuit High Frequency Code.
   • P0339 CKP Sensor Circuit Intermittent.

The most important thing to remember, is that if you get spark from any spark plug wire, the crank sensor is working and the test in this article won't help you. If this is the case, in your particular case, the following tutorial may be of help:

• How To Troubleshoot A No Start (GM 4.3L, 5.0L, 5.7L).

Where To Buy The Crankshaft Position Sensor And Save

The following links will help you comparison for a new crankshaft position sensor:

How The Crankshaft Position Sensor Works

The crankshaft position sensor, on your GM 4.3L, 5.0L, or 5.7L Vortec engine is a Hall Effect type sensor, which in plain English means that it needs a power and a Ground source to produce a signal.

Once the crank sensor produces this signal, the signal is an ON/OFF voltage signal (in DC Volts).

Below, in a nutshell, is how the crankshaft position sensor works in your 4.3L, 5.0L, and 5.7L Chevrolet or GMC (or Olds, Cadillac) pickup or SUV:

1. When you turn the key and start cranking the engine the crank sensor gets 12 Volts on circuit A and Ground on circuit B.
2. A round 'target wheel' attached to the front of the crankshaft and positioned so that it rotates above and in close proximity to the crank sensor, starts to rotate.
3. As the 'teeth' on this target wheel pass by the crank sensor, they start to activate the sensor into creating an ON/OFF pulse.
   • ON is when a tooth on the target wheel passes directly over the sensor, which induces the sensor to create and send a 5 Volt DC pulse.
   • OFF is when that same tooth passes completely away from the crank sensor, which causes the sensor to drop the voltage down to 0 Volts.
4. The PCM uses these ON/OFF 5 Volt pulses to start activating the ignition control module and a host of other things to get your vehicle started.

The most important thing to know about the crank sensor is that if it goes bad, your GM pickup or SUV will 'crank but not start' due to a lack of spark and fuel injection.

In my crankshaft position sensor test instructions, I'll ask you to manually rotate the crankshaft pulley by hand because this is the only way that your multimeter will be able to see these ON/OFF voltage pulses. Using the starter motor will make the multimeter average out these pulses and this type of test result is not as accurate.

TEST 1: Testing The CKP Signal With A Multimeter

The crankshaft position sensor is located on the bottom (passenger-side) of the engine timing chain cover. The very first thing you'll need to do is to verify if the crank sensor is producing a crank signal.

This is a very easy, but accurate test, that will verify the performance of the CKP sensor. But remember (and I know that by now I'm starting to sound like a broken record), this accuracy is accomplished by measuring the crank sensor signal with a multimeter and manually turning the engine by hand, since cranking the engine with the starter motor would not accomplish the same result (unless you use an oscilloscope).

NOTE: The crankshaft position sensor must remain connected to its electrical connector to read the CKP signal. You'll need to use a back probe on the connector or a wire piercing probe on the wire. You can see an example of this tool here: Wire Piercing Probe.

OK, here's the test:

1. 1

   Raise the front of the pick up or SUV and then lower it on jack stands. This will also allow you to comfortably crank the engine manually using a 1/2 ratchet and the appropriate socket.

2. 2

   Disable the fuel system. One way of doing this by disconnecting the Spider fuel injector connector.
   
   This is important! By disabling the fuel injectors, you'll keep the vehicle from possibly starting as you perform the crank sensor test.

3. 3

   Disable the ignition system. You can easily accomplish this by simply disconnecting the ignition coil or the ignition control module. This will prevent the ignition system from creating spark.

4. 4

   Connect the red multimeter test lead to the wire labeled with the letter C in the photo above (with an appropriate tool, like a wire-piercing probe).
   
   The wire (circuit) labeled with the letter C is the one that transmits the CKP sensor signal to the PCM.

5. 5

   Connect the black multimeter test lead to the battery negative (-) terminal.
   
   If you decide to connect the black multimeter test lead to a Ground point somewhere underneath the vehicle, make sure it's a nice clean and rust-free spot.

6. 6

   Turn the key to the ON (RUN) position (but don't crank the engine).

7. 7

   Place your multimeter in Volts DC mode.

8. 8

   Manually turn the engine by hand using a 1/2 inch ratchet and a socket on the crankshaft pulley (turn it clock-wise).

9. 9

   Your multimeter will register an ON/OFF voltage signal as you turn the crankshaft pulley.
   
   ON is when the multimeter displays 5 Volts DC and OFF is when it displays 0 Volts (0.1 Volt equals 0 Volts).

Let's interpret the results of your Crank Sensor Signal Test:

CASE 1: The multimeter registered the ON/OFF voltage as you turned the engine with the ratchet. This is the correct test result and it confirms that the crank sensor is working properly and creating a CKP signal.

No further testing is required since the other two tests in this article check that the crankshaft position (CKP) sensor is getting power and Ground. Since your test confirms that the CKP sensor is creating a signal, then it also proves that it's getting power and Ground.

If you need help diagnosing the no-start condition on your vehicle, the following tutorial may be of help:

• How To Troubleshoot A No Start (GM 4.3L, 5.0L, 5.7L).

CASE 2: The multimeter DID NOT register the ON/OFF voltage signal as you turned the engine with the ratchet. This test result usually confirms that the crankshaft position sensor is bad and needs to be replaced. About 90% of the time this is hitting the nail on the head, but I recommend that you check that the sensor is also getting power and Ground too.

By testing and confirming that the CKP sensor is getting power and Ground, you'll be able to decisively confirm it is bad or that maybe another issue exists, go to: TEST 2: Making Sure The CKP Sensor Is Getting Power.