P1391 Intermittent Loss of CMP or CKP

NAME OF CODE
Intermittent Loss of CMP or CKP

WHEN MONITORED
During engine running.

SET CONDITION
When the expected cam signal level disagrees with the actual cam signal level.

THEORY OF OPERATION
After the engine has been started, the powertrain control module maintains an expected camshaft port level value. At every 69 degree crank edge this value is toggled to reflect the expected change in the cam level. At every crank falling edge, this value is compared to the true camshaft port level. If there is a disagreement between the two values, then the trouble code is matured and set.

At this time, the powertrain centre module is forced back into a spark start and it attempts to synchronize the cam and crank signals.

POSSIBLE INTERMITTENT CAUSES
- Open or shorted 8-volt supply circuit
- Open sensor ground
- Open or shorted signal circuit
- Excessive clearance between the crankshaft sensor and crankshaft pulse ring
- Excessive clearance between the camshaft sensor and the target magnet
- Damaged target magnet
- Damaged crankshaft pulse ring
- Failed sensor
- Failed PCM
- Loose/unlocked CMP/CKP connectors