P0378: Timing Reference High Resolution Signal B Intermittent/Erratic Pulses

Some diesel systems give the injection control a finely divided angle signal in addition to the normal reference signal – the high resolution signal – for precise injection timing and metering. P0378 means a second high resolution signal, B, delivers pulses with erratic spacing or occasional dropouts; it is checked in the same way as signal A (P0370 ff). No manufacturer with a separate signal B was found – GM's diesels with a high resolution signal (6.5-litre, Duramax LB7) only have signal A, and Ford and GM 2014–2019 do not use the codes. The description therefore follows the J2012 name, the analogy to signal A and CARB's monitoring requirement for crank angle sensors. Typically the engine loses power and runs roughly.

Medium severity. Can I keep driving?Drive as little as possible. If you feel jerking or the light flashes, stop: a misfire can damage the catalytic converter.

Symptoms

Check engine light on
Loss of power (limp-home fuelling)
Rough running, hard starting, smoke

Most likely causes

Sensor faulty or dirty
Loose contact or interference in the signal wire
Sensor disc or tone wheel damaged
Engine module

What to check, in order

Start with the simplest. You can tick off each step.

Check the connector and wiring of the coil indicated
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
Check the condition of the spark plug
Swap the coil with another cylinder and see if the code changes
Measure the power supply and control signal using the manufacturer's wiring diagram

Good to know

Repair difficulty: hard
It can trigger limp mode.
It affects emissions.

What each character of P0378 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
3: Ignition and misfires
78: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0378?

Drive as little as possible. If you feel jerking or the light flashes, stop: a misfire can damage the catalytic converter.

What causes code P0378?

The most common causes are: sensor faulty or dirty; loose contact or interference in the signal wire; sensor disc or tone wheel damaged.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.