How The Crank Sensor Works
The crankshaft position sensor, on your Chrysler 2.0L/2.4L equipped car or mini-van, is a Hall-Effect three wire crankshaft position sensor.
Since the crank sensor is a Hall Effect type sensor, it produces an On/Off DC voltage signal that can be easily measured with:
- A multimeter.
- An oscilloscope.
- Or an LED Light.
This also means that there is no crank sensor resistance test to see if the crank sensor is BAD or not. Only the 2 wire reluctor type crank sensor can be resistance tested.
As you turn the key and crank the engine, each one of the three wires that connect to the crank sensor have a specific job to do:
- One delivers power in the form of 5 or 8 Volts from the PCM.
- This thru' the wire labeled with the number 3.
- Another delivers ground. This ground is provided inside the PCM, too.
- This thru' the wire labeled with the number 2.
- The last remaining, delivers the signal, that the CKP sensor creates, to the PCM.
- This thru' the wire labeled with the number 1.
- The PCM uses the crank signal to activate the Auto Shut Down (ASD) Relay.
- The Auto Shut Down (ASD) Relay activates:
- The fuel pump relay and thus the fuel pump.
- The fuel injectors.
- The ignition coil pack and thus spark to each engine cylinder.
- Therefore, the crank sensor (and it's signal) is critical for the engine to start.
The most important thing to know, is that if the crank sensor goes BAD, your Chrysler (or Dodge or Plymouth or Eagle) vehicle will crank but not start due to a lack of spark and fuel injection.
CRANK SENSOR TEST 1: Verifying The CKP Signal
The crankshaft position sensor is located behind the engine (the side facing the vehicle's firewall) above the oil filter adapter. This type of crank sensor goes thru' the block itself and is held securely in place by a bolt.
You'll need to jack up the vehicle to gain access to the crank sensor. Be careful, think safety all of the time, take all precautions. Use a jack stand to hold the car up in the air... do not trust the jack! Wear safety glasses to protect your eyes from falling debris.
The very first thing you do, to start troubleshooting the crank sensor, is to verify that it's either generating a crank sensor signal or not. You'll use a multimeter for this and all parts of the crank sensor test.
Alright, this are the test steps:
Set the parking brake and/or place wheel chocks behind the rear wheels to keep the vehicle from rolling back. Jack up the car or mini-van and place it on jack stands.
Disconnect the four wire connector from the ignition coil pack. This is important! Do not proceed with the test without first unplugging the ignition coil pack.
Locate the CKP sensor's 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.
If it was necessary to unplug the connector from the crank (CKP) sensor to remove some of the black electrical tape insulation... reconnect the connector now. The crankshaft position sensor must be connected to its electrical connector for this test to work.
Place the multimeter in Volts DC mode and with a wire-piercing probe or an appropriate tool, pierce the wire identified with the number 1 in the image viewer, of the three wire connector. Connect the RED multimeter 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.
To see what a what wire piercing probe tool looks like, click here: Wire Piercing Probe.
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.
Connect the BLACK lead of the multimeter to a good ground point on the engine.
When everything is set up, turn the crankshaft pulley by hand in a clock-wise direction while you 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.
If the CKP sensor is working correctly, the multimeter will register an On/Off voltage of 5 Volts DC. On is when the multimeter displays 5 Volts DC and off is 0.5 Volts DC. 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 result indicates that the CKP sensor is creating a good CKP signal and is working fine.
Now, if the crank sensor signal is present and yet your car does not start you'll need to make sure that there's no spark and no fuel injection... since if either of these are present, the crank sensor is not the cause of your vehicle's no start condition.
CASE 2: The multimeter DID NOT register the On/Off 5 Volts DC as the crankshaft pulley was hand-turned: This is not good. The sensor should have produced the indicated On/Off 5 Volt signal. But before we condemn the CKP sensor as BAD, you need to verify that it's getting power and ground. Go to: CRANK SENSOR TEST 2: Verifying Power (5 or 8 Volts).
The next step is to check that the crankshaft position sensor is getting power. This comes in the form of either 5 Volts or 8 Volts, depending on how old your specific Chrysler (or Dodge or Plymouth or etc.) is. The PCM (Powertrain Control Module=Fuel Injection Computer) is the one that provides these 8 Volts to power the crankshaft position sensor.