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 Condition - No Start No Spark Condition.

Here are the contents of this article at a quick glance:

1. Imortant Suggestions.
2. Symptoms of a BAD CKP Sensor.
3. How the Crank (CKP) Sensor Works
4. CKP TEST 1: Crank Signal Test.
5. CKP TEST 2: Power Circuit.
6. CKP TEST 3: Ground Circuit.
7. Related Test Articles.

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 Crank Sensor 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:

1. Multimeter.
   1. You can use a Digital Multimeter or an Analog Multimeter although the Digital one is the preferred one.
   2. If you don't have a Multimeter or need to upgrade yours, check out my recommendation here: Abe's Multimeter Recommendation (at: easyautodiagnostics.com).
2. 1/2 inch Ratchet Wrench
3. Socket that will fit Crankshaft Pulley Bolt.
4. 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 Condition’. 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:
   1. The Ignition Coil will not Spark.
   2. No Spark from all of the Spark Plug Wires.
   3. 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:
   1. P0336 CKP Sensor Circuit Performance.
   2. P0337 CKP Sensor Circuit Low Frequency Code.
   3. P0338 CKP Sensor Circuit High Frequency Code.
   4. 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.