The crank position sensor on a Pontiac Bonneville is a four-wire sensor that contains two hall effect switches with one shared magnet. The sensor receives 10 to 12 volts from the ignition control module (ICM). The crank sensor supplies a 3X and an 18X signal to the ICM at six pulses per crankshaft revolution. This signal is used by the ignition module to determine crankshaft position relative to cylinder number 1 to synchronize coil firing sequence.
The sensor is located behind the crankshaft pulley. The best test connection is at the ICM connector. There are 14 wires in the connector. If the car will not start, take a volt and ohmmeter and switch it to a low-volt scale. Look at the harness going into the ICM. There are seven wires on both sides of the center screw holding the connector into the ICM. This test is to see if the crank sensor is working or not, causing a no start. Probe the first wire to the left of the screw. This is the 3X signal and ground. Have a helper try to start the car. A duty cycle should show on the voltmeter in the form of fast flashes of 0 to 12 volts as the engine turns over. If there is no voltage or the voltage is out of range, you will need to do a couple more tests to confirm that it is bad or to determine what the problem is.
Probe the third wire in from the outside of the left side of the connector. This is the ICM wire. Touch the other probe to a good ground. Turn the key on. The voltage should show less than 100 milivolts. If the voltage shows as 100 milivolts, turn the key off and disconnect the harness connector at the crank sensor. Probe the first wire, starting on the outside edge of the ICM connector on the left side. This is the 12-volt supply to ground. With the key on, there should be battery voltage. If the sensor failed the test for 100 milivolts or less and showed to have battery voltage in the last test the sensor is bad. If it passed all of the tests, then the ICM is bad.
