TEST 2: Verifying The Crank Sensor Is Getting Power
Like any other electrical component on your Dodge pickup (van or SUV), the crankshaft position sensor needs power and Ground to work.
In this test section, you'll check that the crank sensor is getting power with your multimeter.
To give you some more specifics, this power is in the form of 5 Volts DC and are provided by the PCM with the key on (and of course with the key on engine running).
The PPL/WHT (purple/white) wire of the crank sensor's engine wiring harness connector is the one that feeds these 5 Volts to the crank sensor.
This is what you need to do:
With your multimeter in Volts DC mode, probe the wire identified with the number 1 in the image viewer, with red multimeter test lead.
NOTE: Do not probe the front of the crank sensor connector to verify this voltage. Back probe the connector or pierce the wire with an appropriate tool.
Ground the black lead of the multimeter to a good Ground point on the engine.
Turn the key to the on position, no need to crank the engine with the starter motor.
Your multimeter should register 4.5 to 5 Volts DC, if all is good and the PCM is feeding power to this circuit.
Let's take a look at your test results:
CASE 1: The multimeter registered 5 Volts DC when the key was turned On. This let's you know that the CKP Sensor is being fed with power 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: TEST 3
CASE 2: The multimeter DID NOT register 5 Volts DC when the key was turned On. Recheck your connections and try the test again.
If the multimeter still does not register 5 Volts, then you now have confirmed that the lack of power is the reason why the crank sensor is not working (and so replacing it will not help solve the problem).
Although it's beyond the scope of this article to find the cause of this lack of power (to the crank sensor), solving the issue that is causing these missing 5 Volts will solve the no start condition of your 3.9L, 5.2L, or 5.9L equipped Dodge pickup (van or SUV).
TEST 3: Verifying The Crank Sensor Is Getting Ground
So far, if you've reached this point... you have:
One: Confirmed that the crank sensor is not producing an on/off voltage signal.
Two: Verified that the PPL/WHT wire of the harness connector is feeding the crank sensor with 5 Volts DC.
In this last test section, you'll check that the sensor is getting Ground with a simple multimeter voltage test.
IMPORTANT: Be very careful not to short this wire to battery voltage, or you'll fry the PCM. Also, do not use a test light to verify this voltage. Use a multimeter.
Alright, this is what you'll need to do:
Place your multimeter in Volts DC mode and with the black multimeter test lead, probe the BLK/LT BLU (black/light blue) wire of the crank sensor's engine wiring harness connector.
NOTE: Do not probe the front of the crank sensor connector to check this Ground. Back probe the connector or pierce the wire with an appropriate tool.
Connect the red lead of your multimeter to the battery positive terminal.
When everything is set up, have your helper turn the key to the On position.
If Ground is being fed to the crank sensor on this wire, your multimeter should register battery voltage (12+ Volts).
Let's interpret your specific test results:
CASE 1: The multimeter registered 12 Volts DC when the key was turned On. This test result tells you that the BLK/LT BLU wire is feeding the crank sensor with ground. Taking into account the results from the previous 2 tests (and this one), you can conclude that the crank sensor is bad and needs to be replaced.
Here's why: A good working crank sensor, when it receives power and Ground and the engine is cranking, will generate an On/Off 5 Volt Signal. Now, in your particular case:
- In TEST 1 you verified the crank sensor is not creating its ON/OFF 5 Volt Signal.
- In TEST 2 you confirmed that it's being fed with power (5 Volts) and in this test step, you have verified that it's getting a good ground
- ... therefore the crank sensor is bad and replacing the crank sensor will solve the cranks but does not start issue.
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 let's you know that the BLK/LT BLU wire is not feeding the crank sensor with ground. You have now eliminated the crank sensor as the cause of the no start condition, since without this Ground, the crank sensor will not work.