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.

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