How Do I Check a Crankshaft Position Sensor?
by Dan FerrellThe Crankshaft Position (CKP) sensor monitors crankshaft position and speed. Your vehicle computer uses this information, along with data from other vehicle sensors, to maintain ignition timing. As a result, problems with the crank sensor or circuit will prevent the engine from starting. If you suspect a bad CKP on your car, follow this guide to test the unit and, if necessary, replace it.
Testing
With your CKP sensor, you can test for voltage output and compare the results to manufacturer specifications. If your voltmeter comes with needle probes, back probe the wires at the sensor connector. If this is not possible, unplug the sensor electrical connector and plug the two halves to a test connector or a couple of jumper wires. Then plug back the connector.
Set your digital multimeter to AC milivolts range and have a helper crank the engine. A typical sensor will have an output above 200 mV. However, you should compare your results with the specifications listed in the service manual for your particular vehicle.
If your service manual gives a resistance value, you can test the sensor without having to crank up the engine. Unplug the sensor and connect the meter probes to each sensor wire connector. Set your meter to Ohms and compare your reading to the resistance value specified in your service manual. If your voltage or resistance values are out of specifications, replace the sensor.
If your test results are within specifications, check the sensor electrical connector and wiring harness. It is common for loose connectors or broken wires to keep the sensor from communicating with the Engine Management System (EMS). Also, make sure to check the trigger wheel. The wheel, located on the crankshaft or damper, may have missing or damaged teeth. Any of these parts or components may trigger a CKP sensor or circuit trouble code.
Replacing the Sensor
Look for the CKP sensor at the front or side of the engine (see Resources). It is usually held in place by a single bolt. Lift the front of your vehicle using a floor jack and support it on two jack stands. Then unplug the sensor electrical connector and remove the bolt with a ratchet and socket.
When installing the new unit, make sure the mounting surface is completely clean to keep the exact distance from the tip of the sensor to the trigger wheel. On some particular models, you might need to adjust the sensor air gap, or its distance from the wheel, before locking the unit in place. If necessary, follow the instructions on your particular vehicle manual for this adjustment.
References
- The Haynes Emissions Control Manual; Mike Stubblefield and John H. Haynes; 2001
- Modern Automotive Technology; James E. Duffy; 2003
Writer Bio
Since 2003 Dan Ferrell has contributed general and consumer-oriented news to television and the Web. His work has appeared in Texas, New Mexico and Miami and on various websites. Ferrell is a certified automation and control technician from the Advanced Technology Center in El Paso, Texas.
