P0371: Timing Reference High Resolution Signal A Too Many 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. P0371 means signal A delivers more pulses than expected within the reference window – for example more high resolution pulses per reference pulse than the nominal ratio, which on GM's 6.5-litre diesel is 64 ± 4 per cam pulse; the usual cause is interference pulses. No manufacturer document available to us uses P0371: GM's 6.5-litre diesel (optical sensor in the injection pump) reports all faults of its high resolution track under P0370 and the Duramax LB7 uses only P0370 and P0374. The description therefore follows the J2012 name, GM's description of the signal 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 P0371 means

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

Frequently asked questions

Can I keep driving with code P0371?

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

What causes code P0371?

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.