If the crank sensor fails, in your 4.8L, 5.3L or 6.0L GM vehicle... it's not gonna' start. In this article, I'll show you how to test it using a multimeter (in Volts DC mode).
The crank sensor test in this article is an On Car Test. It's not possible to do a simple resistance test of the crank sensor. Why? Well, it's because this crank sensor is a Hall Effect type and these can not be ohmed (to find out if they're good or not).
Contents of this tutorial:
Tools You'll Need:
- Jack Stands
- 1/2 inch Ratchet Wrench
Important Tips And Suggestions
TIP 1: To perform the test, you'll need to manually turn the engine. The best point, to turn the engine with a 1/2 ratchet wrench and a socket, is the crank pulley.
You'll need to lift the vehicle to gain access to the crank pulley. Use jack stands to hold up the vehicle... DO NOT trust the jack. Your safety is your responsibility, so take all necessary safety precautions (which include using safety glasses).
TIP 2: Do not turn the engine with the starter motor, when doing the crank sensor test. Using the starter motor will severely decrease the accuracy of your multimeter test results.
TIP 3: If your GM vehicle starts and runs... the crank sensor is good, and this article will not help you.
TIP 4: Since this is an On Car Test of the crank sensor, DO NOT remove the crank sensor to test it. In the photo you'll notice it's out but this is just to make it easier to explain the test to you.
Symptoms Of A BAD Crank Sensor
The one symptom that's gonna' be staring you right in the face is your GM pick up or van or SUV cranking but not starting.
More specifically, you'll see one or all of the following symptoms when the crank sensor fails:
- No spark from all of the Coil-on-Plug Ignition Coils.
- No fuel injector pulses from the fuel injector connectors as tested using a Noid Light.
- On that rare occasion the PCM stores a Diagnostic Trouble Code:
- P0335: No Crank Sensor Signal Detected.
- P0336: Inconsistent Crank Sensor Signal Detected.
The thing to remember about having a failed crank sensor, is that if you have spark or fuel injector pulses, the crank sensor is OK and not the cause of your No Start Condition.
How The Crank Sensor Works
The crankshaft position sensor, on your 4.8L, 5.3L, 6.0L GM vehicle, is a Hall-Effect three wire crankshaft position sensor. As such it has 3 wires coming out of its connector.
This also means that this type of crank sensor creates an On/Off DC voltage signal that can be easily measured with a multimeter, an Oscilloscope, and even an LED Light. In this article, I'll show you how to test the crank sensor with a multimeter.
Each one of the three wires that connect to it have a specific job to do. In a nutshell this is what happens when you turn the key and crank the engine:
- One wire delivers power in the form of 12 Volts from the PCM.
- This is the wire labeled with the letter C.
- Another delivers ground. This ground is provided inside the PCM, too.
- This is the wire labeled with the letter B.
- As the engine turns, a reluctor wheel on the crankshaft activates the crank sensor into creating its On/Off voltage signal 24 times per crankshaft revolution.
- This crank signal is fed to the PCM on:
- Wire labeled with the letter A.
- The PCM now uses this crank signal to:
- Activate the 8 COP coils to spark.
- Activate all 8 fuel injectors to start spraying fuel into the cylinders.
- Maintain the fuel pump activated after its initial start.
- With fuel and spark now present, the engine now starts.
The most important thing to know, is that if the crank sensor goes BAD, your 4.8L, 5.3L, 6.0L GM vehicle vehicle will ‘Crank but Not Start’.