Damaged or contaminated timing reference wheel (missing teeth, debris, or corrosion); Faulty crankshaft or camshaft position sensor for signal 'B'; Wiring harness damage such as chafed wires, corroded connectors, or poor grounds; Excessive air gap between the sensor and the reluctor wheel; Mechanical timing chain or belt wear causing the signal to drift or skip; ECM internal fault or software issue (rare but possible)

DTC codes / P03xx · Ignition system and misfire / P0377

P0377Timing Reference High Resolution Signal 'B' Too Few Pulses

Q: What does code P0377 mean?

Timing Reference High Resolution Signal 'B' Too Few Pulses. P0377 means the engine control module (ECM) is receiving too few pulses from the high-resolution timing reference signal 'B', which is usually a fine-toothed crank or cam sensor wheel used for precise injection and ignition timing. The ECM compares expected pulse counts against what it actually sees and sets this code when the signal drops out or is intermittently missing.

P0377 means the engine control module (ECM) is receiving too few pulses from the high-resolution timing reference signal 'B', which is usually a fine-toothed crank or cam sensor wheel used for precise injection and ignition timing. The ECM compares expected pulse counts against what it actually sees and sets this code when the signal drops out or is intermittently missing.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaIgnition system and misfire

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Rough idle or misfire at low engine speeds
Hard starting or a crank-no-start condition in severe cases
Reduced engine power or limp-home mode
Poor fuel economy or increased emissions
Intermittent stalling when the signal drops out momentarily

Common causes, most likely first

Damaged or contaminated timing reference wheel (missing teeth, debris, or corrosion)
Faulty crankshaft or camshaft position sensor for signal 'B'
Wiring harness damage such as chafed wires, corroded connectors, or poor grounds
Excessive air gap between the sensor and the reluctor wheel
Mechanical timing chain or belt wear causing the signal to drift or skip
ECM internal fault or software issue (rare but possible)

How to diagnose and fix it

Scan all modules for stored and pending codes, then record freeze-frame data to see when the fault occurs
Inspect the sensor and reluctor wheel visually for damage, debris, or missing teeth
Check the sensor air gap with a feeler gauge and compare to specification
Perform a wiggle test on the sensor wiring and connectors while monitoring live pulse count data
Measure sensor resistance and compare to the manufacturer's specification
Use an oscilloscope to verify the signal waveform for missing or distorted pulses
If the signal is clean at the sensor but not at the ECM, repair the harness; if the signal is bad at the sensor, replace the sensor or reluctor wheel

What the pulse count really tells you

A dirty or magnetized reluctor wheel often mimics a failed sensor, so clean the wheel before condemning the sensor.
Intermittent faults frequently come from a loose connector or a wire rubbed through near a sharp bracket, not from the sensor itself.
Some engines use the same signal for both cam and crank reference, so a fault in one circuit can set codes for the other.
A stretched timing chain can cause the pulse count to drift without any sensor fault, so always verify mechanical timing.
The ECM may set P0377 only after a certain number of missed pulses, meaning the fault can be present but not yet stored as a hard code.

Can I keep driving with P0377?

You can usually drive short distances to a repair shop if the engine runs smoothly, but avoid heavy acceleration or long trips because a sudden loss of timing signal can cause stalling or a no-start. If the engine is misfiring or stalling, stop driving and have it towed.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.