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P0376Timing Reference High Resolution Signal "B" Too Many Pulses

The engine computer is counting more pulses on the secondary (Signal B) high-resolution timing reference than it expects per engine revolution.

Definition

The PCM compares the number of high-resolution timing pulses received between low-resolution reference marks; Signal "B" is the secondary high-resolution channel. P0376 sets when extra pulses are counted, which usually indicates electrical noise being induced onto the circuit or a damaged trigger wheel creating false edges. The engine may run rough, buck, or set incorrect timing because the PCM cannot reliably locate crankshaft position, and the MIL illuminates with possible fallback to a default timing mode.

Common causes

  • Electrical noise/EMI induced into the signal wiring from ignition wires or alternator
  • Chafed harness insulation allowing intermittent contact with another circuit
  • Damaged trigger wheel with burrs or debris creating false pulse edges
  • Failing position sensor producing ragged, noisy output
  • Poor sensor shield or engine ground connections
  • Faulty PCM input circuit (rare)

Common misdiagnoses

  • Position sensor replaced when the real cause was ignition-noise pickup from failing plug wires
  • Injection pump or distributor replaced for what was a routing/shielding problem
  • PCM replaced without checking grounds and shield drains
  • Trigger wheel replaced when the harness was inducing the extra pulses

Troubleshooting steps

  1. 1.Check harness routing

    Confirm the sensor wiring is not bundled with or routed within an inch of spark plug wires, coil drivers, or alternator output cables.

  2. 2.Scope the signal for noise

    Watch the pulse train on a lab scope at idle and under load; extra narrow spikes riding between legitimate pulses confirm induced noise rather than a mechanical fault.

  3. 3.Verify shield and ground integrity

    Check that any drain/shield wire is grounded at one end only per the diagram, and measure less than 0.1V drop on sensor and PCM grounds.

  4. 4.Inspect secondary ignition components

    On gasoline engines, look for carbon-tracked coils or leaking plug wires, since arcing secondary voltage is a classic source of false timing pulses.

  5. 5.Inspect the trigger wheel

    Look for burrs, dents, or metallic debris stuck to the reluctor teeth that could create extra sensor edges.

  6. 6.Substitute a known-good sensor

    If noise persists on the scope with clean wiring and grounds, replace the sensor and re-scope to confirm a clean pulse count.

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