P0371 Timing Reference High Resolution Signal "A" Too Many Pulses

The P0371 diagnostic trouble code means that the engine control module (ECM/PCM) has detected more pulses than expected from the Timing Reference High Resolution Signal “A” circuit.

This is a timing-reference problem involving the high-resolution signal used by the engine computer to determine precise engine speed and rotational position.

The ECM expects a specific pulse pattern as the engine rotates. When it detects additional pulses that should not be there, the timing information may no longer match the expected pattern.

P0371 does not automatically mean the timing sensor is defective. The cause can be the sensor, wiring, connector, electrical interference, incorrect sensor installation, a damaged or incorrect trigger target, or a mechanical timing problem.

What Is a High-Resolution Timing Reference Signal?

The ECM needs extremely precise information about engine rotation.

Timing reference sensors generate a sequence of electrical pulses as a crankshaft, camshaft, or another timing target rotates. The ECM analyzes these pulses to determine engine position and speed.

This information can be used to control:

• Ignition timing

• Fuel injection timing

• Engine speed

• Crankshaft position

• Camshaft synchronization

• Variable valve timing

• Misfire detection

• Fuel and ignition calculations

The term “High Resolution” refers to a timing signal containing many position references during engine rotation. This allows the ECM to determine rotational position much more precisely.

The exact source of Signal “A” is manufacturer-specific. It may come from a crankshaft-related sensor, camshaft-related sensor, dedicated timing pickup, or another timing-reference system.

What Does “Too Many Pulses” Mean?

The ECM expects a particular number and pattern of pulses from Signal A.

If additional pulses are detected, the ECM may determine that the timing signal does not correspond to the expected pattern and store P0371.

The additional pulses can be caused by:

• Electrical noise

• A distorted sensor signal

• A faulty sensor

• Incorrect sensor installation

• An incorrect sensor air gap

• A damaged trigger wheel

• A damaged reluctor

• Wiring problems

• Poor grounding

• Signal interference

• Incorrect timing components

• Mechanical timing problems

The important distinction is that “too many pulses” describes the signal received by the ECM. It does not necessarily mean that the engine is physically rotating too quickly.

Why Would Extra Pulses Be a Problem?

The ECM uses the timing pulses as positional references.

If the control module interprets electrical noise or an abnormal waveform as additional timing events, it may calculate engine position incorrectly.

That can affect:

• Spark timing

• Fuel injection timing

• Camshaft synchronization

• VVT control

• Engine speed calculation

• Misfire detection

The severity depends on how many extra pulses are detected and how the particular engine uses Signal A.

Some vehicles may continue running with only a Check Engine Light, while others can experience noticeable drivability problems.

Symptoms of P0371

Possible symptoms include:

• Check Engine Light

• Difficult starting

• Extended cranking

• Intermittent no-start

• Rough idle

• Hesitation

• Poor acceleration

• Reduced engine power

• Unstable RPM

• Engine stalling

• Misfire

• Poor fuel economy

• Incorrect ignition timing

• Incorrect fuel injection timing

• Variable valve timing problems

• Limp-home mode

In mild cases, the driver may notice very little.

If the timing information becomes sufficiently inaccurate, however, the engine can run poorly or even stall.

Can P0371 Cause a No-Start?

Yes, it can.

If Signal A is critical for engine synchronization, an incorrect pulse pattern may prevent the ECM from establishing reliable engine position.

The engine may crank normally but fail to start because the ECM cannot determine when ignition or fuel injection should occur.

However, this behavior is not universal. Some engine-management systems have alternative timing references and can continue operating despite a Signal A problem.

Common Causes of P0371

Faulty timing reference sensor

An internal sensor fault can produce an abnormal waveform containing extra transitions that the ECM interprets as additional pulses.

Electrical interference

This is particularly important with a “Too Many Pulses” code.

Electrical noise can create additional signal transitions that resemble legitimate timing pulses.

Possible sources include:

• Ignition components

• Alternator problems

• Poor grounds

• Damaged wiring

• Improperly routed harnesses

• Aftermarket electrical equipment

Damaged wiring

A signal wire with damaged insulation may intermittently contact another electrical circuit and introduce unwanted transitions into the timing signal.

Poor connector contact

Loose or corroded terminals can distort the signal and cause the ECM to interpret the waveform incorrectly.

Poor sensor ground

A poor ground can alter signal quality and make a normally functioning sensor produce an abnormal waveform.

Incorrect sensor installation

An improperly positioned sensor can produce an unstable or distorted signal.

The correct sensor-to-target distance is important on many timing systems.

Damaged reluctor or trigger wheel

A timing target with damaged, bent, cracked, loose, or contaminated teeth can create an incorrect pulse pattern.

Incorrect timing component

If the wrong trigger wheel, reluctor, or timing component has been installed, the ECM may receive a pulse pattern that does not match its calibration.

Mechanical timing problem

A timing chain or belt problem can alter the relationship between the timing components and the sensor.

ECM/PCM problem

The control module itself can potentially misinterpret a correct signal, but this should be considered only after the sensor, wiring, waveform, trigger mechanism, and mechanical timing have been properly tested.

P0371 Does Not Automatically Mean a Bad Sensor

This is one of the most important aspects of diagnosing this code.

P0371 describes what the ECM sees, not necessarily which component has failed.

For example, a perfectly functional timing sensor could generate P0371 if the signal wire is picking up electrical interference.

Likewise, the sensor may be working correctly while a damaged reluctor creates an abnormal pulse pattern.

Simply replacing the sensor without checking the signal can therefore result in an unnecessary repair.

How to Diagnose P0371

A systematic approach is recommended.

1. Scan all modules

Check for stored, pending, and manufacturer-specific codes.

Pay particular attention to codes related to:

• Crankshaft position

• Camshaft position

• Engine synchronization

• VVT

• Misfire

• Engine speed

• Ignition

• Fuel injection

• Communication

Additional codes can help determine whether P0371 is an isolated signal problem.

2. Review freeze-frame data

Look at the conditions under which P0371 was recorded.

Useful information includes:

• Engine RPM

• Engine temperature

• Battery voltage

• Engine load

• Vehicle speed

• Starting or running condition

If the code appears only at high RPM, for example, the signal may become distorted as engine speed increases.

3. Identify Signal A

The meaning of Signal “A” is not universal.

Use the manufacturer's wiring diagram and service information to determine:

• Which sensor produces Signal A

• Sensor technology

• Connector pinout

• Power supply

• Ground

• Signal wire

• Trigger mechanism

• Expected waveform

Do not assume that Signal A always refers to a particular crankshaft or camshaft sensor.

4. Inspect the sensor and connector

Check for:

• Bent pins

• Corrosion

• Loose terminals

• Oil contamination

• Water intrusion

• Damaged connector locks

• Physical sensor damage

• Incorrect mounting

Also inspect the sensor's position relative to its timing target.

5. Inspect the wiring

Follow the harness from the sensor toward the ECM.

Look for:

• Chafing

• Broken insulation

• Heat damage

• Pinched wires

• Poor previous repairs

• Aftermarket splices

• Contact with ignition wiring

• Contact with moving components

Signal wiring should be routed according to the manufacturer's design because timing signals can be sensitive to electrical interference.

Check for Electrical Noise

Because P0371 specifically indicates too many pulses, electrical interference deserves particular attention.

An oscilloscope can show whether the signal contains unwanted transitions.

For example, a normal signal might contain clean transitions between its high and low states.

If electrical noise creates additional transitions, the ECM could interpret some of them as additional timing pulses.

A basic multimeter may completely miss this behavior because it cannot display the detailed waveform.

Oscilloscope Testing

An oscilloscope is one of the most useful tools for diagnosing a high-resolution timing fault.

The technician can examine:

• Pulse frequency

• Pulse spacing

• Signal amplitude

• Signal shape

• Electrical noise

• Additional transitions

• Missing pulses

• Signal dropouts

• Changes at different RPM

The signal should also be compared with the manufacturer's known-good waveform where available.

A waveform that looks correct at idle but develops additional transitions at higher RPM can provide a very strong clue.

Check Power and Ground

If the sensor requires external power, verify the supply according to the manufacturer's specifications.

The ground should also be checked under operating conditions.

A poor ground can introduce instability into a timing signal.

Voltage-drop testing can be useful for identifying high-resistance connections that may appear normal during a basic voltage measurement.

There is no universal voltage specification for P0371 because sensor designs differ between vehicles.

Inspect the Trigger or Reluctor

If the electrical circuit is healthy, inspect the physical timing target.

Depending on the engine, this could be:

• Reluctor wheel

• Trigger wheel

• Tone wheel

• Crankshaft target

• Camshaft target

• Timing gear

• Manufacturer-specific timing component

Look for:

• Damaged teeth

• Bent components

• Cracks

• Loose mounting

• Excessive contamination

• Incorrect installation

• Incorrect target configuration

A trigger wheel that does not match the engine's calibration can produce a signal that appears electrically plausible but contains the wrong number of timing events.

Can a Timing Chain Cause P0371?

A mechanical timing problem can contribute to timing-reference faults, although the exact relationship depends on the engine.

Potential problems include:

• Stretched timing chain

• Incorrect timing-chain installation

• Damaged timing sprocket

• Loose timing component

• Incorrect camshaft timing

• Damaged reluctor

• VVT malfunction

If P0371 occurs with camshaft/crankshaft correlation codes, abnormal timing-chain noise, difficult starting, or sudden stalling, mechanical timing should be investigated.

Hall-Effect vs Variable-Reluctance Sensors

Timing sensors use different technologies.

A Hall-effect sensor generally requires an electrical supply and produces a digital switching signal.

A variable-reluctance sensor generates an alternating electrical signal as the magnetic field changes when the timing target passes the sensor.

The correct diagnostic procedure depends on the sensor type.

For this reason, there is no universal resistance, voltage, or waveform value that can be applied to every vehicle with P0371.

Always use the specifications for the particular vehicle and engine.

Could Low Battery Voltage Cause P0371?

Low voltage can sometimes contribute indirectly to timing signal problems.

If system voltage becomes unstable, sensor operation and signal processing can be affected.

However, low battery voltage is not a typical reason to assume that the ECM is simply receiving “too many pulses.”

If there are voltage-related symptoms, check:

• Battery condition

• Cranking voltage

• Battery terminals

• Engine grounds

• Starter operation

• Charging-system voltage

P0371 vs Other Timing Reference “A” Codes

The related codes describe different abnormalities in Signal A.

P0370 – Timing Reference High Resolution Signal “A” Malfunction

A general malfunction is detected in Signal A.

P0371 – Timing Reference High Resolution Signal “A” Too Many Pulses

The ECM detects more pulses than expected.

P0372 – Timing Reference High Resolution Signal “A” Too Few Pulses

The ECM detects fewer pulses than expected.

P0373 – Timing Reference High Resolution Signal “A” Intermittent

The Signal A timing reference becomes intermittent or erratic.

P0374 – Timing Reference High Resolution Signal “A” No Pulses

The expected Signal A pulses are not detected.

This distinction can help direct the diagnostic process. With P0371, particular attention should be paid to signal quality, electrical interference, incorrect trigger configuration, and extra signal transitions.

Can P0371 Be Intermittent?

Yes.

The code describes the ECM detecting too many pulses, but the underlying problem can occur only under certain conditions.

For example, extra pulses may appear:

• At high engine RPM

• During acceleration

• When the engine becomes hot

• During heavy electrical loads

• When the wiring vibrates

• When the engine moves under load

• When an electrical component switches on

This is why freeze-frame data and testing under the conditions that triggered the code are valuable.

Is It Safe to Drive With P0371?

If the engine starts easily, runs smoothly, and the Check Engine Light remains steady, a short drive to a repair facility may be possible.

However, a timing-reference fault should not be ignored.

If the signal becomes increasingly inaccurate, the vehicle may develop:

• Stalling

• Hard starting

• Misfires

• Loss of power

• No-start conditions

Driving should be avoided if the engine is already stalling, severely misfiring, or experiencing major power loss.

A Practical Diagnostic Sequence

A useful diagnostic path for P0371 is:

P0371 → scan all codes → review freeze-frame → identify Signal A → inspect sensor → inspect connector → inspect wiring → verify power and ground → check for electrical interference → observe the waveform → inspect the trigger/reluctor → check synchronization → investigate mechanical timing if necessary → repair → clear codes → road test → verify the signal remains correct.

This sequence is particularly important because replacing a timing sensor without checking the waveform can easily miss an electrical interference or trigger-wheel problem.

Final Thoughts

P0371 – Timing Reference High Resolution Signal “A” Too Many Pulses means that the ECM/PCM is detecting more timing pulses than it expects from the monitored high-resolution Signal A circuit.

The cause can be a faulty sensor, but it may also be a wiring problem, poor ground, connector issue, electrical interference, incorrect sensor installation, damaged reluctor, incorrect timing component, or mechanical timing problem.

Because the defining symptom is extra pulses, signal-quality testing is especially valuable. An oscilloscope can reveal additional electrical transitions and noise that a conventional scan tool or multimeter may not show.

The correct diagnosis should therefore focus on what the Signal A waveform actually looks like, why the ECM is interpreting additional pulses, and whether the physical timing mechanism matches the manufacturer's specifications.