P0377 Timing Reference High Resolution Signal B Too Few Pulses

P0377 indicates too few pulses in Timing Reference High Resolution Signal B. The B channel is losing expected timing events.

Code details

Generic OBD-II · P0

System: Ignition / Misfire
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not chase fuel delivery or ignition output first if the timing reference B signal is missing pulses.

Symptoms of P0377

Rough idle, shaking, or a stumble under acceleration.
A flashing check-engine light during an active misfire.
Power loss and higher fuel consumption.

Common causes of P0377

Worn spark plugs, ignition coils, or plug wires.
Fuel-delivery problems — injectors, pressure, or a lean/rich mixture.
Vacuum leaks, low compression, or a mechanical fault in that cylinder.

Useful checks before replacing parts

Compare signal B pulse count against signal A, crank and cam sync, freeze-frame RPM, no-start history, and intermittent stall symptoms.
Inspect weak sensor output, excessive air gap, damaged trigger wheel sections, open signal wiring, loose terminals, and poor sensor power or ground.
Capture signal B during cranking, heat soak, and road-load conditions to determine when pulses are missing.

Related OBD-II codes

These nearby ignition / misfire entries can help compare wording and pin down the fault area.