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P0377 — Timing Reference High Resolution Signal B Too Few Pulses

Generic OBD-II · all makesPowertrain (engine & transmission)

The code indicates the engine control module is receiving too few high‑resolution pulses from the camshaft position sensor circuit, which is used to determine engine timing. Insufficient pulses can cause timing errors and affect engine operation.

Symptoms

What causes it — most likely first

1. Camshaft position sensor failure

The sensor may be defective or its signal weak, causing the control module to detect insufficient pulses.

2. Damaged wiring or connector

Corroded, broken, or loose wiring/connector to the sensor can interrupt the high‑resolution signal.

3. Timing belt or chain problems

A stretched, slipped, or worn timing belt/chain can misalign the camshaft, reducing pulse count.

4. Faulty engine control module

A malfunctioning PCM can misinterpret the sensor signal, but this is uncommon and typically only after other causes are ruled out.

How it's diagnosed

  1. Inspect the camshaft position sensor wiring and connectors for damage or corrosion.
  2. Measure sensor resistance and signal voltage with a multimeter or oscilloscope while the engine runs.
  3. Check the timing belt or chain condition and tension to ensure proper camshaft alignment.
  4. Verify that the sensor signal meets manufacturer specifications using a scan tool data stream.
  5. If the sensor and wiring are good, test the PCM input circuit for proper voltage and ground.
  6. Replace the camshaft position sensor if it fails the signal test, then clear the code and retest.

Code facts & related codes

SystemPowertrain (engine & transmission)
StandardizationSAE generic — identical on every make
Related codesP0370 — Timing Reference High Resolution SignaP0371 — Timing Reference High Resolution SignaP0372 — Timing Reference High Resolution SignaP0373 — Timing Reference High Resolution SignaP0374 — Timing Reference High Resolution SignaP0375 — Timing Reference High Resolution Signa

Frequently asked

Can a faulty camshaft position sensor cause P0377?

Yes, a defective sensor or poor signal is the most common cause of this code.

Is the PCM usually the cause of P0377?

No, the PCM rarely fails; most issues are due to the sensor, wiring, or timing components.

Do I need to replace the timing belt to fix this code?

Only if the belt is stretched, damaged, or out of service interval; otherwise the belt is not the primary cause.

Will clearing the code fix the problem?

Clearing the code without repairing the underlying fault will cause it to return once the issue persists.