18X REFERENCE SIGNAL MISSING
The 18X signal (circuit 647) is used by the PCM to improve ignition timing accuracy during crank and at engine speeds of up to 2000 RPM. The 18X signal circuit allows the use of EST mode below 400 RPM, eliminating the need to utilise bypass mode during startup, and also allows the PCM to calculate true crankshaft position in 1/6 the time that use of the crankshaft reference signal would permit.
During normal operation, the PCM uses the 18X signal to control ignition timing until the engine speed exceeds 2000 RPM, at which time the crankshaft reference signal (circuit 430) is used. When conditions for setting DTC 47 exist, the crankshaft reference signal is used by the PCM to control EST. This condition will cause bypass mode to be used for ignition timing below 400 RPM and EST ignition timing to be degraded below 2000 RPM.
DTC 47 will set if:
The engine is running.
The PCM detects 240 (80 crank revolutions) crankshaft reference pulses, and no 18X signal pulses.
The engine RPM is below 1200.
DTC 47 does not illuminate the "Check Powertrain" lamp.
Test Description: Number(s) below refer to step number(s) on the diagnostic chart.
4. If a window on the harmonic balancer is interfering with the 18X Hall-Effect switch, the ignition module will earth the 18X signal. Starter may have to be bumped several times to obtain a voltage reading.
5. Voltage reading should be lower than that obtained with engine not running, indicating a pulsed reference signal.
8. Verifies that circuit 647 is not shorted to earth or open in the harness.
An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation.
Backed out connector terminals or broken down insulation in circuit 647.
If connections and harness check OK, try monitoring voltage on circuit 647 with DVM while moving the related wiring harness and connectors with the engine idling. This may help to isolate the location of the malfunction.