The crank sensor (crankshaft position sensor) is one of the most important sensors that the PCM in your Dodge pickup (van, SUV, or 1994-96 Jeep Grand Cherokee) relies on to start and keep the engine running.
So when this bad boy fails, you'll have a bona-fide cranks but does not start condition on your hands.
Thankfully, testing the crank sensor isn't hard and it can be done very accurately with a multimeter. In this tutorial I'll show you how in a step-by-step way.
Contents of this tutorial:
NOTE: This tutorial only covers 1994, 1995, and 1996 Dodge 3.9L, 5.2L and 5.9L pick ups, vans and SUVs. For the 1997 and up Dodge vehicles, the following crank sensor test tutorial may be of help:
Important Tips And Suggestions
TIP 1: The crank sensor test I'm gonna' show you in this tutorial is done while the sensor is in its place on the transmission's bell housing. No need to remove it to test it.
TIP 2: To perform this test and get a very accurate result you can trust, I'm gonna' ask you to crank the engine by hand. This is super important, because if you use the starter motor to crank the engine- you're not gonna' get an accurate result.
By cranking the engine by hand, I mean turning the engine using a 1/2 ratchet wrench and an appropriate socket on the crank pulley.
TIP 3: One of the most important things to keep in mind, when testing the crank sensor on your 3.9L, 5.2L, or 5.9L Dodge pickup (van, SUV), is that if you have tested for spark and you are getting spark, then the crank sensor is OK. A spark result tells you that the crank sensor is doing it's job. In a case like this (where you're getting spark), this test will not help you.
This also means that you should test for spark first.
OK, let's get testing.
TEST 1: Verifying The Crank Signal With A Multimeter
The very first thing you'll do is to see if the crank sensor is producing an on/off 5 volt signal on its sensor signal circuit.
Since the crank sensor has to remain connected to its harness connector for this test to work, you'll need to tap into this wire.
You can do this one of two ways. The first is to back-probe the connector. The other is to use a wire-piercing probe. To see what this tool looks like, take a look at: Wire Piercing Probe Tool Review (Power Probe PWPPPPP01).
NOTE: As mentioned at the beginning, you don't need to remove the crank sensor to test it and it's very important that YOU DO NOT REMOVE it to test it. If you do, 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 -it will get beaten to death by the flywheel's reluctor ring.
OK, let's get started:
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.
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).
Locate the crank sensor's connector.
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 crank sensor. Remove enough of this electrical tape insulation to gain comfortable access to the three wires it protects.
Place the multimeter in Volts DC mode and connect the red multimeter test lead to the GRY/BLK wire of the crank sensor harness connector.
This is the wire that connects to terminal number 3 of the crank sensor harness connector identified in the illustration above.
Connect the black multimeter test lead to a good Ground point on the engine or directly on the battery negative (-) post.
Turn the Key to the On position (but don't crank the engine), since this will power up the crank sensor and make the test work.
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. Do not use the starter motor to crank the engine, since this will defeat the accuracy of this test.
If the crank sensor is good, then your multimeter should show you an On/Off voltage of 5 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 interpret the results of your crank sensor test:
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 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: TEST 2: Verifying The Crank Sensor Is Getting Power.