FixItFor.Us
P codepowertrainHigh severity

P0375Timing Reference High Resolution Signal "B" Malfunction

The engine computer has detected a general fault in the secondary (Signal B) high-resolution timing reference signal it uses for precise ignition or injection timing.

Definition

The PCM times spark or fuel injection using high-resolution pulse trains generated by the crankshaft or camshaft position sensing system; Signal "B" is the secondary high-resolution channel, used on applications with dual timing signals (including some GM diesels where the signal originates inside the injection pump). P0375 sets when the pulses on this channel are missing, distorted, or inconsistent with the low-resolution reference signal. Symptoms include hard starting, stalling, rough running, hesitation, and reduced power, and the MIL illuminates; the PCM may fall back to a default timing strategy or the engine may not run at all if the signal is unusable.

Common causes

  • Failed high-resolution crankshaft or camshaft position sensor (on GM 6.5L diesels, the optical sensor inside the injection pump)
  • Chafed, open, or shorted wiring in the sensor circuit
  • Corroded or loose connector terminals at the sensor or PCM
  • Damaged or contaminated reluctor/trigger wheel
  • Electrical interference from ignition components or poor grounds
  • Faulty PCM (rare)

Common misdiagnoses

  • Injection pump replaced when the fault was in the harness or connector
  • Crankshaft position sensor A replaced when the B-channel circuit was at fault
  • Battery or charging system blamed for stalling symptoms
  • PCM replaced without scoping the actual signal

Troubleshooting steps

  1. 1.Record freeze frame and check for companion codes

    Note RPM and temperature when the code set, and whether Signal A codes (P0370-P0374) or CKP/CMP codes are also present, which points to a shared cause.

  2. 2.Scope the Signal B circuit

    Backprobe the high-resolution signal wire with a lab scope while cranking and running; you should see a clean, evenly spaced square-wave or AC pulse train with no dropouts.

  3. 3.Inspect wiring and connectors

    Check the harness from the sensor to the PCM for chafing against brackets, and look for green corrosion or spread terminals at both connectors.

  4. 4.Test sensor supply and ground

    Verify the sensor receives its specified reference voltage (typically 5V or battery voltage per the wiring diagram) and has less than 0.1V of drop on its ground circuit.

  5. 5.Inspect the trigger wheel or optical disc

    Look for bent, missing, or debris-packed teeth on the reluctor, or oil contamination of an optical sensor, and confirm the sensor air gap is within spec.

  6. 6.Wiggle-test while monitoring live data

    Flex the harness and tap the sensor with the engine running while watching the scope or scan data for dropouts that reproduce the fault.

Related codes