P0371
Timing Reference High Resolution Signal A Too Many Pulses
When a vehicle powertrain module registers the fault code P0371, it points directly to an internal system malfunction identified as "Timing Reference High Resolution Signal A Too Many Pulses". Operating your engine under this condition may degrade long-term fuel maps.
Driver's Summary
P0371 is triggered when the PCM detects an abnormal condition associated with timing reference high resolution signal a too many pulses. The most common signs are engine surging, erratic tachometer, stalling. Stop driving as soon as it is safe to do so. This fault can lead to expensive secondary damage if left unaddressed.
Symptoms
Engine surging, erratic tachometer, stalling
Common Causes
- Electrical interference from bad spark plug wires
- Faulty optical sensor
- Debris inside the distributor
- Failing alternator causing AC ripple
How to Fix
- 1 Reroute or replace spark plug wires
- 2 Replace optical sensor
- 3 Clean or rebuild distributor
- 4 Test alternator AC ripple
Technical Explanation
P0371 is stored after the control module confirms the fault over multiple ignition cycles, ruling out transient electrical noise as the cause. For injector-specific codes, the ECM monitors the injector control circuit voltage drop during each pulse; a shorted or open injector presents a characteristic resistance signature that differs measurably from a healthy unit. Once confirmed, the code is stored as a permanent DTC and the MIL is activated. The freeze frame snapshot — recording RPM, load, coolant temperature, and fuel trim at fault detection — is also saved and is critical for accurate diagnosis.
Is It Safe to Drive?
With P0371 active, your engine or transmission is not operating within design parameters. Short-term driving may seem fine, but internal damage is accumulating — particularly to electrical interference from bad spark plug wires.
Mechanic's Pro Tip
The most common mistake with P0371 is replacing the sensor without verifying the reference voltage and ground integrity first. Use a scan tool to monitor the sensor's live output; a truly failed sensor shows a stuck, flatlined reading — a sensor that fluctuates but reads slightly off usually indicates a wiring or vacuum issue, not a dead sensor. Always spray electrical contact cleaner on the connector pins before condemning the sensor.
Plug wires: 50 - 150; Sensor/Distributor: 200 - 400