Note. For circuit reference, see WIRING DIAGRAMS - 4.3L article.
Circuit Description
The Crankshaft Position (CKP) sensor sends pulses to PCM as the reluctor teeth rotate past the CKP sensor. PCM uses the CKP pulses to synchronize ignition and fuel injector operation, and to time interval between each CKP pulse. PCM 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, PCM 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.
PCM learns variations during CKP system variation learning procedure. PCM compensates for these variations when performing detect misfire calculations. Only a scan tool can command PCM to perform CKP system variation learning procedure again.
Perform learning procedure after the following actions
- VCM replacement
- Any operation or repair involving crankshaft, CKP sensor or CKP sensor-to-reluctor wheel gap relationship
- Engine replacement
- Ignition switch left in ON position until battery is 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.
Conditions for setting DTC
- Engine running.
- No CKP or CMP sensor DTCs present.
- PCM has not learned the CKP system variation.