P0378 Timing Reference High Resolution Signal B Intermittent/Erratic Pulses

P0378 points to intermittent or erratic pulses in Timing Reference High Resolution Signal B. The secondary high-resolution timing reference is unstable.

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 close P0378 based only on static resistance checks; intermittent timing signals need dynamic testing.

Symptoms of P0378

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 P0378

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

Review RPM instability, stall or surge complaints, freeze-frame data, signal B status, and whether the concern follows heat, vibration, or moisture.
Inspect connector tension, wiring flex points, shielding, sensor mounting, trigger wheel condition, grounds, and harness routing near high-current circuits.
Record the waveform during the failure condition to identify erratic spacing, dropout, or noise on the B signal.

Related OBD-II codes

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