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P0379Timing Reference High Resolution Signal "B" No Pulses

The engine computer is receiving no pulses at all from the secondary (Signal B) high-resolution timing reference signal.

Definition

The PCM monitors the Signal "B" high-resolution timing channel whenever the engine is rotating and sets P0379 when the channel is completely silent while the low-resolution reference signal shows the crankshaft turning. A total loss of the high-resolution signal usually means an open circuit, a dead sensor, or loss of sensor power. Depending on the application the engine may crank but not start, start and run in a degraded default-timing mode with noticeably reduced power, or stall and restart; the MIL illuminates in all cases.

Common causes

  • Failed position sensor with no output (open coil or dead Hall element)
  • Open circuit in the signal wire between sensor and PCM
  • Loss of sensor supply voltage or ground (blown fuse, open feed)
  • Unplugged or badly corroded connector
  • Sheared or missing reluctor/trigger wheel key
  • Faulty PCM input circuit (rare)

Common misdiagnoses

  • Fuel delivery components replaced for a no-start caused by the missing timing signal
  • Injection pump condemned when the sensor feed circuit was open
  • Starter or battery blamed for a crank/no-start
  • PCM replaced before checking sensor power and ground

Troubleshooting steps

  1. 1.Confirm the failure while cranking

    Scope Signal B during cranking; zero activity while the low-resolution reference signal toggles confirms the B channel alone is dead.

  2. 2.Check sensor power and ground

    With the key on, verify the specified supply voltage (5V or battery voltage per the diagram) at the sensor connector and a good ground with under 0.1V drop.

  3. 3.Test circuit continuity

    With both ends disconnected, ohm the signal wire from sensor connector to PCM pin; expect less than 1 ohm and no continuity to ground or power.

  4. 4.Bench-test or substitute the sensor

    Measure a magnetic sensor's coil resistance against spec, or substitute a known-good sensor, and re-scope for output.

  5. 5.Verify the trigger wheel turns

    Confirm the reluctor is present, keyed, and actually rotating with the shaft — a sheared key leaves a good sensor with nothing to read.

  6. 6.Check the PCM pin

    If wiring and sensor test good, backprobe the signal at the PCM connector; a signal present at the pin with the code still setting indicates a PCM input fault.

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