OBD-II Code P0371 — What It Means & How to Fix It

What Does This Error Mean?

P0371 means the PCM is receiving more timing pulses from the high-resolution reference signal A than it expects in one crankshaft revolution. Extra pulses confuse the PCM's calculation of engine position, leading to inaccurate fuel and ignition timing. Expect rough running, misfires, reduced power, and potentially difficult starting.

Affected Models

Older GM vehicles — late 1990s and early 2000s trucks and cars with the high-resolution timing system
Common in GM Vortec V8 trucks from 1996-2007
Common in some GM V6 engines with the secondary timing reference
Less common on foreign-make and modern vehicles
Most frequently seen on high-mileage older trucks that have had distributor or timing work done

Common Causes

Damaged or cracked tone wheel with a chipped tooth creating a false extra pulse
Metal debris or ferrous material on the tone wheel creating additional magnetic disturbances
Incorrect tone wheel installed during a previous repair — wrong tooth count
Sensor mounted too close to the tone wheel, picking up reflected or bounce pulses
Electrical interference from nearby wiring causing extra pulses on the signal wire

How to Fix It

Locate the high-resolution timing sensor A and remove it. Inspect the tone wheel (reluctor ring) it reads from. Look carefully for a chipped, cracked, or partially broken tooth. Even a small chip can generate an extra pulse on every revolution.

Use a bright light and look at every tooth systematically. A damaged tooth is not always obvious at a glance. Run your finger around the wheel to feel for any irregularity.
Check for metal debris on the tone wheel. Ferrous particles attracted to the magnetic sensor or stuck between teeth can mimic an extra tooth. Carefully clean the tone wheel with a rag and inspect again after cleaning.

Do not use a wire brush directly on the tone wheel as it can scratch the surface and create new irregularities. Use a clean cloth and brake cleaner or a gentle solvent.
Verify the sensor air gap is within specification. A sensor mounted too close to the tone wheel can pick up the return magnetic field from a tooth that has already passed, creating a double-pulse effect. Measure the gap with a feeler gauge and adjust if needed.

The air gap spec is usually 0.5 to 1.5 mm. Consult your service manual for the exact specification for your engine. A gap that is too small is as problematic as one that is too large.
Check for wiring that runs parallel and close to the sensor signal wire for long distances. Electrical interference from spark plug wires or ignition components can induce phantom pulses on an unshielded signal wire. Reroute any suspected interfering wires away from the sensor circuit.

This type of interference was more common on older ignition systems with conventional spark plug wires. If you have recently changed plug wires, verify they are routed away from the timing sensor harness.
If the tone wheel has visible damage, the wheel must be replaced. This may require removing a harmonic balancer, flywheel, or distributor depending on where the tone wheel is located on your specific engine. After repair, clear codes and verify normal sensor operation with a scanner.

On some GM engines, the high-resolution reluctor ring is part of the crankshaft or camshaft assembly. Consult your service manual for the correct replacement procedure before beginning disassembly.

When to Call a Professional

Too-many-pulses codes usually indicate a physical tone wheel or sensor gap problem. A technician with a lab scope can view the actual signal pattern and quickly identify whether a tooth is damaged or whether noise in the circuit is causing phantom pulses. Diagnosis runs $80-$150. Tone wheel replacement can be involved on some engines and may require significant disassembly.

Frequently Asked Questions

How does the PCM know there are too many pulses?

The PCM knows exactly how many pulses it should receive from the high-resolution sensor for each full crankshaft revolution based on the tooth count on the tone wheel. If it counts more pulses than expected before the crankshaft completes one revolution, it sets P0371. This count mismatch tells the PCM that either the sensor is receiving phantom signals or the physical tone wheel is damaged.

Can P0371 be caused by a previous repair?

Yes — and this is actually common. If someone replaced the distributor, crankshaft, or timing components with an incorrect part, the new tone wheel may have a different tooth count than expected. A wrong-tooth-count reluctor ring will consistently produce too many or too few pulses and cause these codes every time the engine runs.

Is driving with P0371 safe?

Short distances are okay, but the fuel and ignition timing is being calculated from incorrect data. This means the engine is not running efficiently and could produce more emissions than normal. Extended driving with incorrect timing data can stress engine components and reduce fuel economy significantly. Get it diagnosed and repaired within a few days.