CKP TEST 1: Verifying The CKP Signal
The very first thing, that you need to do, is to see if the crank sensor is producing a crank signal and you can do this with a multimeter.
By now, if you've done any research in a repair manual or on the Internet, you know that the crank sensor is located on the transmission bell housing.
Fortunately, to test the crank sensor, you don't need to remove it and it's very important that YOU DO NOT REMOVE it to test it. Why? -because the sensor's air gap calibration will get lost.
What this means is that if you remove it and then re-install the same crank sensor, the sensor's air gap will be lost and it will get beaten to death by the flywheel's reluctor ring.
OK, let's get started:
- 1
Disable the ignition system by disconnecting the ignition coil.
This step is important do not proceed to the next step until you've done this. - 2
Disable all of the fuel injectors.
This step is important also, since this will prevent the PCM from injecting fuel into the engine cylinders (if the crank sensor is OK). - 3
Locate the crank sensor's connector. This connector will be on the side of the engine that houses the spark plugs.
Once you've located the crank sensor connector, 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. - 4
Place the multimeter in Volts DC mode.
- 5
With a wire-piercing probe or an appropriate tool, pierce the wire identified with the number 1 of the three wire connector (see photo above).
Connect the red multimeter test lead to this tool. The wire labeled with the number 1 is the signal wire that transmits the crank (CKP) sensor signal to the PCM.
On the Grand Cherokee, this is a red with light green stripe (RED/LT GRN) wire. On the Jeep Wrangler, this is a gray with black stripe (GRY/BLK) wire. - 6
Connect the black multimeter test lead to battery negative (-) terminal.
- 7
Turn the key to the ON position (but don't crank the engine). This will power up the crankshaft position sensor and make the test work.
- 8
When the multimeter's leads are all set up, have a helper (if necessary) turn the crankshaft pulley by hand in a clock-wise direction.
Your job is to keep your eyes glued on the multimeter's display.
NOTE: Do not use the starter motor to crank the engine, since this will defeat the accuracy of this test. - 9
Your multimeter should show you an ON/OFF voltage of 5 Volts/0 Volts DC as the crank pulley is turned by hand.
OFF is when your multimeter reads 0 Volts and ON is when it reads 5 Volts. The key to seeing this voltage change is to turn the crankshaft pulley slowly and steadily.
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 5 Volts DC as the crankshaft pulley was hand-turned. This is good and this result tells you that the crank sensor is working OK at this point in time.
So now you know that your troubleshooting tests have to take a different path since the crank sensor is not the cause of the no-start condition.
CASE 2: The multimeter DID NOT register the ON/OFF 5 Volts DC as the crankshaft pulley was hand-turned. This tells you that the crank sensor is not producing a crank signal the PCM can use (to create spark and to inject fuel).
In about 95% of the cases, you can conclude the crank sensor is fried and replace it, and it will solve the no-crank condition. But (yeah, I know) not always.
Therefore, the next step is to check that the crankshaft position sensor is getting power. This comes in the form of 5 Volts and from the PCM (Powertrain Control Module = Fuel Injection Computer). Go to: CKP TEST 2: The Power Circuit.
