How Do Camshaft Sensors Work?

by Don Bowman

A camshaft sensor is a 3-wire hall effect switch which is usually mounted at the front of the camshaft, in the timing cover. Not all vehicles have it located in the front; it may also be somewhere along the axis of the camshaft. On some Japanese vehicles, the cam shaft sensor is in the distributor and looks like a small CD. A common problem on Hondas is where oil from the camshaft gets past the O-ring and into the distributor, contaminating it and causing a no start.

The primary purpose of the cam sensor is to generate a signal indicating top dead center on number 1 cylinder for the ECM to use to manage the sequential fuel injection and for misfire detection. This is on most domestic vehicles; however, Honda and several other Japanese vehicles also use the cam sensor to control the ignition profile.

If the camshaft fails on most cars, the computer, in lieu of a cam signal, will take a best guess and the car will still run but with a considerable lack of performance and gas mileage. This is called the limp home mode. On a Honda or an Acura there are 7 wires at the distributor: yellow-green stripe (ignition input); blue (crankshaft +); green (top dead center +); yellow (camshaft +); white (crankshaft -); red (top dead center -); and black (camshaft -). This is pretty consistent on most foreign cars with a distributor that houses the crank and cam sensors. Use this wire indicator to check for power in a no start and also to check the sensors' operations. On most of the domestic cars, the sensor handles the sequential fuel injection and misfire detection. It is a 3-wire connector with inconsistent color combinations, so remember that the center wire in the connector is the ICM. The outside wire on one side will be camshaft + with 10 volts, and the other side is the signal: camshaft signal to ICM; ICM + (10 volts); and ICM (this will be the middle wire in the connector.

About the Author

Don Bowman has been writing for various websites and several online magazines since 2008. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam).

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