Vanden Plas L6-4.0L (1990)
Crankshaft Position Sensor: Component Tests and General Diagnostics
CRANKSHAFT SENSOR CIRCUIT
There is no ECM OBD monitoring of this circuit. Intermittent loss of the signal will cause engine misfire and/or stalling. Total loss will stop the
engine completely.
The crankshaft sensor, located on the engine front timing cover, produces an AC voltage. The sensor output voltage to the ECM will increase
rapidly as engine speed increases from cranking to running.
Possible Faults
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Incorrect sensor core gap.
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Open circuit or short Circuit wiring between ECM and crankshaft sensor.
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Poor ground connection between the sensor shielding and bulkhead ground stud.
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Defective crankshaft sensor.
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Damaged toothed wheel.
Diagnostic Notes
1. The crankshaft sensor signal can be monitored with an oscilloscope.
2. The crankshaft AC voltage output can be measured between ECM yellow connector pins 13 and 24:
2.5 volts AC at 1000 rpm (approximate).
5.0 volts AC at 3000 rpm (approximate).
3. The sensor coil resistance should be 1.25 to 1.45 kilo ohms at 21°C (70°F). Replace the sensor if the resistance is incorrect.
4. The sensor air gap should be 0.5-1.0 mm (0.020-0.040 in). If the gap is incorrect, remove the mounting bracket from the engine and the
crankshaft sensor from the mounting bracket. File the mounting bracket to reduce the core gap. Install the assembly and recheck the gap.
5. To check the crankshaft sensor circuit, disconnect the ECM yellow connector and the crankshaft sensor connector. Check for an open
circuit or a short circuit to ground between the ECM yellow connector pin 13 (RED wire) and the crankshaft sensor connector, and the
ECM yellow connector pin 24 (BLUE wire) and the crankshaft sensor connector.
6. Check the crankshaft sensor shield connection to ground at the harness side of the crankshaft sensor connector pin 2.
7. If an engine misfire is accompanied by erratic tachometer readings, suspect a poor crankshaft sensor output.
