How to Replace a Crank Shaft Sensor

by David Eiranova

For a car's engine to run, the spark plugs must fire precisely when the piston reaches the top of the compression stroke. Modern cars use a crankshaft position sensor (or crank shaft sensor) to regulate the firing of the spark plugs, but in times past, this was achieved with a distributor. Today's engines use a Distributorless Ignition System (DIS) or electronic ignition, which relies on the crankshaft position sensor to guide the sequential firing of the spark plugs. Faulty crank shaft sensors will cause the engine to not run (or run poorly) and should be replaced.

Disconnect the battery ground (negative) cable to prevent accidental shorts that could damage the electronic control module.

Find the crankshaft position sensor. It may be on the front of the engine, on the side or in the rear. A shop manual should be able to tell you where it is for your car's year, make and model.

Disconnect the three wires that lead to the crankshaft sensor. One of these is the current feed, and the other two are the ground wire and the sensor's output. Keep track of which is which--They will connect to the corresponding places on the replacement sensor.

Remove the crankshaft position sensor. If it is mounted on the front of the engine, the sensor will typically be fitted into a bracket hole and will be secured with a small bolt, which must be removed.

Install the replacement sensor and connect the three wires. Most sensors lock into position and do not require adjustment. If the sensor is on the side of the engine, you will likely need to install a new rubber O-ring. Do not reinstall the O-ring that came off when the old sensor was removed. For the handful of crankshaft position sensors that need adjustment, you can often use a paper spacer placed on the end of the sensor. When finished, reconnect the battery.

Tip

  • check The crankshaft position sensor may not be the cause of engine trouble, so it is essential to properly diagnose the problem before replacing the sensor. For post-1995 cars with on-board diagnostic capabilities, you can connect a scanner to check for trouble codes relating to the crank shaft sensor.

Warning

  • close If you are replacing a sensor that uses an O-ring, make sure there is no debris around the sensor, because that might cause the sensor to operate improperly.

Items you will need

References

About the Author

A reporter since 2005, David Eiranova wrote for "The Lunenburg Ledger," from 2007 to 2009 and has served as a correspondent for "The Lowell Sun." He holds a Bachelor of Arts in economics. Since 2007 he has been the director of publicity for the Acton Community Chorus.