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P codepowertrainMedium severity

P0371Timing Reference High Resolution Signal "A" Too Many Pulses

The PCM is counting more high-resolution timing pulses per crankshaft revolution than the system should produce.

Definition

The PCM counts the pulses on the high-resolution timing reference circuit and compares the total per revolution against the known design count (for example 360 pulses). P0371 sets when too many pulses are counted, which means extra transitions are appearing on the circuit — almost always electrical noise induced into the signal wiring or a damaged trigger disc creating false edges. Symptoms include intermittent stumble, surging, inaccurate spark timing, possible false misfire detection, and a MIL.

Common causes

  • Ignition noise induced into the signal circuit from faulty plug wires or coil arcing
  • Damaged shielding or drain wire on the high-resolution signal circuit
  • Cracked or contaminated optical trigger disc creating extra signal edges
  • Chafed harness intermittently shorting and generating false pulses
  • Failing sensor or optical pickup producing a noisy output
  • Poor engine or PCM ground allowing electrical noise on the reference

Common misdiagnoses

  • Sensor or distributor replaced when secondary ignition arcing is inducing the noise
  • PCM replaced for an interference problem
  • Fuel-system parts replaced for noise-induced surging
  • New signal sensor installed without repairing broken circuit shielding

Troubleshooting steps

  1. 1.Inspect the secondary ignition

    Check plug wires and coil boots in the dark for arcing to ground — leaking secondary voltage is the classic source of extra counted pulses.

  2. 2.Check signal wire routing and shielding

    Verify the high-resolution circuit is routed away from plug wires and that any shield drain wire is intact and grounded at one end only, per the service manual.

  3. 3.Scope the signal for noise

    Look for spikes or double transitions riding on the square wave at idle and while snapping the throttle; correlate noise bursts with ignition events.

  4. 4.Verify grounds

    Voltage-drop test the engine-to-body and PCM grounds (under 0.1 V while cranking); poor grounds raise the noise floor on signal circuits.

  5. 5.Inspect the trigger disc or reluctor

    On optical systems, examine the slotted disc for cracks, oil film, or debris that could create false edges.

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