No Crank Reference Signal at PCM

NO CRANK REFERENCE SIGNAL AT POWERTRAIN CONTROL MODULE (PCM).

When Monitored
During engine cranking, with battery voltage less than 11.5V and manifold vacuum present.

Set Condition
No signal from the crank position sensor is present during engine cranking, or the cam position signal is present with no crank signal.

Theory of Operation
The crank position sensor is a hall effect-type sensor used to detect the crankshaft speed and position. The PCM supplies 8 volts from cavity 7 to power up the sensor. Sensor ground is provided by PCM cavity 4. The PCM also supplies a 5-volt pull-up voltage to the sensor from cavity 24. The sensor signal is created by the slots cut in the flywheel passing under the sensor. When a slot is under the sensor, the signal is high (5V). When the metal between the slots is under the sensor, the signal is low (0.3V).

Possible Causes
- Open or shorted 8-volt supply circuit.
- Open sensor ground.
- Open or shorted signal circuit.
- Excessive clearance between the sensor and flywheel.
- Damaged flywheel.
- Failed sensor.
- Failed PCM.