Circuit Description

The Crankshaft Position (CKP) sensor sends pulses to VCM as the reluctor teeth rotate past the CKP sensor. VCM uses the CKP pulses to synchronize ignition and fuel injector operation, and to time interval between each CKP pulse. VCM determines when an excessive change in crankshaft speed occurs by comparing each new time interval with previous interval.

A misfire causes an unexpected change in crankshaft speed. A certain amount of acceleration/deceleration is expected between each firing stroke, but if crankshaft speed changes more than expected amount, VCM interprets this as a misfire. Interval between CKP sensor pulses is extremely small. At high engine speeds, slight variations in the crankshaft, reluctor and CKP sensor components make misfire detection difficult.

VCM learns variations during CKP system variation learning procedure. VCM compensates for these variations when performing detect misfire calculations. Only a scan tool can command VCM to perform CKP system variation learning procedure again. Perform learning procedure after VCM replacement, any operation or repair involving crankshaft, CKP sensor or CKP sensor-to-reluctor wheel gap relationship, engine replacement or when ignition switch was left in ON position until battery drained.

NOTE: Removing power to VCM with ignition on may clear/erase stored pulse value and set this DTC.

Reprogramming VCM does not require running the CKP system variation learn procedure unless VCM is new or from another vehicle. DTC will set when VCM has not learned the crankshaft position system variation.