CKP TEST 1: Verifying The Crank Signal
In case you're wondering, the crank sensor is located on the passenger side of the engine, right beside the starter motor (or behind the starter motor, depending on your point of view).
To be able to test the crank sensor you'll need to remove the starter motor. The starter motor can remain off of the engine for the remainder of the test.
OK, let's get started:
- 1
Jack up your GM vehicle and set it up on jack stands. Disconnect the battery and remove the starter motor.
- 2
If you have completely removed the starter motor, you'll need to wrap the starter's main battery cable with black electrical tape. This is important, since you'll need to reconnect the battery for the test. If this starter motor cable is left hanging and unprotected, it may short out on the engine block.
- 3
Disable the fuel system. You can easily do this by removing the fuel pump relay that's located in the underhood fuse box.
- 4
Locate the crank sensor and disconnect it from its connector. Now, remove some of the plastic wire loom protector and/or the black electrical tape that shields the three wires of the CKP sensor. Remove enough of this electrical tape insulation to gain comfortable access to the three wires it protects.
Do not remove the crank sensor from the engine block. - 5
Place the multimeter in Volts DC mode and with a wire-piercing probe or an appropriate tool, pierce the wire identified with the letter A in the image viewer, of the three wire connector. Connect the red multimeter test lead to this tool.
To see what a what wire piercing probe tool looks like, click here: Wire Piercing Probe.
This is the wire that delivers the crank signal to the PCM. Don't worry about the particular color this wire should be on your vehicle. You'll be able to identify it easily with the photo in the image viewer. - 6
Reconnect the connector to the crank sensor. The crankshaft position sensor must be connected to its electrical connector for this test to work.
- 7
Ground the black multimeter test lead to a good Ground point on the engine.
- 8
When everything is set up, have a helper turn the crankshaft pulley by hand in a clock-wise direction.
Keep your eyes on the multimeter. Do not use the starter motor to crank the engine, since this will defeat the accuracy of this test. - 9
If the CKP sensor is working correctly, the multimeter will register an ON/OFF voltage. Off will be 0 Volts and On will be 10 Volts.
Alright, let's find out if you have a bad CKP sensor on your hands or not. Choose from the CASES below that best match your specific results:
CASE 1: The multimeter registered the ON/OFF DC voltage as the crankshaft pulley was hand-turned: This is the correct and expected result and tells you that the crank sensor is working good. The crank sensor is not the cause of your no-start condition.
CASE 2: The multimeter DID NOT register the ON/OFF pulses as the crankshaft pulley was hand-turned: Recheck all of your connections. If still no ON/OFF 10 Volt pulses on the multimeter, it looks like the crank sensor is bad.
The next step is to check that the crankshaft position sensor is getting power. This comes in the form of 12 Volts. Go to: CKP TEST 2.
CKP TEST 2: Verifying Power (12 Volts)
So far, in TEST 1, you have confirmed that the crank sensor is not creating a crank signal.
So, in this test step, you're gonna' verify that the crank sensor is getting power.
Since the crank sensor on your GM vehicle is a Hall Effect type sensor, it needs an external power source to create its signal. This power comes in the form of 12 Volts.
In this test step you'll check it with your multimeter and this is what you'll need to do:
- 1
With the red multimeter test lead, probe the wire identified with the letter C in the image viewer. Now, set your multimeter in Volts DC mode.
As before, pierce the wire with an appropriate tool. - 2
Ground the black multimeter test lead to a good Ground point on the engine.
- 3
When everything is set up, have your helper turn the key to the On position.
- 4
If all is good with this circuit, your multimeter should register 12 Volts.
OK, let's interpret the multimeter test results you just obtained. Choose from the CASES below that best match your specific results:
CASE 1: The multimeter registered 12 Volts DC when the key was turned On. This let's you know that the CKP sensor is being fed with power (12 Volts) from the PCM. There is still one more test to do, before we can condemn the crank sensor as bad, and that is to test the Ground circuit. Go to CKP TEST 3
CASE 2: The multimeter DID NOT register 12 Volts DC when the key was turned On. Recheck your connections and try the test again.
If the multimeter still does not register 12 Volts, then this result lets you know that the reason that the crank sensor did not produce a signal, in TEST 1, is because the crankshaft position (CKP) sensor is not getting power. You have now eliminated the crank sensor as the cause of the no-start condition.
Solving the issue that is causing these missing 12 Volts will solve the no-start condition of your 4.8L, 5.3L, 6.0L GM vehicle.
