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P0371 Code: Timing Reference High-Resolution Signal “A” Too Many Pulses

P0371 means the PCM counted excessive high-resolution timing pulses. Learn how to diagnose signal noise, sensor faults and encoder damage.

The P0371 OBD-II trouble code means the powertrain control module counted more pulses than expected from Timing Reference High-Resolution Signal “A.”

This signal provides precise engine-position information for fuel-injection and ignition timing. Depending on the vehicle, it may come from an optical sensor inside a diesel injection pump, a distributor pickup, a crankshaft or camshaft sensor, or another manufacturer-specific timing-reference device.

P0371 is not simply a failed crankshaft sensor code. It specifically means the PCM detected an excessive number of pulses, false waveform edges or an incorrect pulse pattern during a defined engine rotation.

Common causes include electrical interference, damaged signal shielding, a cracked encoder disc, an incorrect replacement sensor, connector problems or a failing high-resolution timing sensor.

P0371 Code Quick Reference

ItemDetails
CodeP0371
DefinitionTiming Reference High-Resolution Signal “A” Too Many Pulses
SystemEngine-position and timing reference
Fault typeExcessive pulse count
Common applicationsDiesel injection-pump and manufacturer-specific timing systems
Common symptomsHard starting, stalling, misfires and reduced power
Common causesSignal noise, encoder damage or defective sensor
Repair urgencyHigh
Safe to drive?Limited driving only if the engine operates normally

What Does the P0371 Code Mean?

The PCM relies on timing-reference signals to determine the exact rotational position and speed of the engine.

A high-resolution signal uses many electrical pulses per revolution. These closely spaced pulses allow the PCM to calculate precise timing for:

The PCM expects to receive a specific number of pulses during each engine or pump revolution.

P0371 is stored when it receives more pulses than the calibrated number.

The extra pulses may be caused by:

In plain language, the PCM counted timing events that should not exist.

What Is High-Resolution Signal “A”?

High-Resolution Signal A is a detailed position signal generated by a pulse-producing sensor and rotating target.

Possible signal sources include:

Signal A does not universally identify one physical sensor. The exact source depends on the vehicle manufacturer, engine and fuel system.

Use vehicle-specific service information to determine:

How Does a High-Resolution Timing Signal Work?

A high-resolution system uses a rotating encoder or trigger wheel divided into many small segments.

As each segment passes the sensor:

  1. The sensor changes its electrical output.
  2. The signal switches between high and low states.
  3. The PCM recognizes the transition as a pulse.
  4. The PCM counts the pulses.
  5. Pulse spacing is converted into speed and position.
  6. Fuel or ignition timing is adjusted accordingly.

The PCM may compare Signal A with:

The number and spacing of pulses must remain consistent.

If electrical noise inserts extra transitions, the PCM may count one real pulse as two or more events. A damaged encoder can also generate unexpected changes that resemble additional pulses.

How an Optical Timing Sensor Produces Pulses

Some diesel injection systems use an optical sensor and slotted encoder disc.

The system typically includes:

As the disc rotates, its slots repeatedly allow and block light. The optical receiver converts those changes into electrical pulses.

P0371 may occur when:

Do not disassemble an injection pump without the correct service procedure and calibration equipment.

What Does “Too Many Pulses” Mean?

The PCM has a programmed expectation for the number of pulses generated during a defined timing window.

For example, if the calibrated pattern contains a specific number of high-resolution slots per revolution, the PCM expects that exact count.

P0371 may be triggered when the PCM sees:

This is different from a basic high-voltage code. Signal voltage may stay within its normal range while the pulse count remains wrong.

Symptoms of P0371

Possible symptoms include:

Some PCMs can ignore the high-resolution signal and operate using a lower-resolution backup. Others may be unable to maintain accurate injection or ignition timing.

Common Causes of P0371

Possible causes include:

  1. Failed high-resolution timing sensor
  2. Defective optical timing sensor
  3. Incorrect replacement sensor
  4. Damaged optical encoder disc
  5. Cracked encoder slot
  6. Loose or wobbling encoder
  7. Damaged reluctor wheel
  8. Bent or duplicated trigger edge
  9. Excessive sensor air gap
  10. Sensor mounted incorrectly
  11. Metal debris on a magnetic sensor
  12. Electrical noise in the signal circuit
  13. Damaged signal shielding
  14. Signal wire routed near ignition wiring
  15. Signal wire routed near injector power circuits
  16. Signal wire routed near alternator output wiring
  17. Loose sensor connector
  18. Corroded connector terminals
  19. Bent or pushed-back pins
  20. Poor sensor ground
  21. Unstable sensor supply voltage
  22. Signal wire shorted to another pulsed circuit
  23. Incorrect wiring repair
  24. Damaged injection-pump harness
  25. Excessive shaft movement inside the injection pump
  26. Incorrect injection-pump installation
  27. Mechanical timing problem
  28. PCM input-circuit failure
  29. Incorrect PCM calibration
  30. Aftermarket electronics creating interference

How Serious Is the P0371 Code?

P0371 should be treated as a high-priority engine-timing fault.

False timing pulses can cause the PCM to calculate incorrect engine position. Depending on the vehicle, this may affect injection timing, ignition timing and engine synchronization.

Possible consequences include:

Stop driving if:

P0371 vs P0370

P0370 identifies a general High-Resolution Signal A malfunction.

P0371 is more specific.

CodeMeaning
P0370General high-resolution Signal A malfunction
P0371Signal A contains too many pulses

P0370 should retain the broad explanation of signal sources, circuit architecture and general waveform failures.

P0371 should focus on:

P0371 vs P0372

P0371 and P0372 identify opposite pulse-count conditions:

Extra pulses often point toward electrical noise, double-triggering or unexpected encoder edges.

Too few pulses more commonly suggest missing encoder slots, weak sensor output, excessive air gap or a signal that fails to switch.

P0371 vs P0373

P0373 indicates intermittent or erratic pulses from High-Resolution Signal A.

P0371 specifically means the PCM counted too many pulses.

A continuously noisy signal that produces extra edges may set P0371. A connector that briefly interrupts the pulse train may set P0373.

The codes can appear together if the waveform both drops out and produces false transitions.

P0371 vs P0374

P0374 means the PCM detects no High-Resolution Signal A pulses.

P0371 means the opposite problem: pulses exist, but the PCM receives more than expected.

A completely open circuit may set P0374. A signal wire picking up ignition noise may set P0371.

P0371 vs P0335

P0335 identifies a Crankshaft Position Sensor A circuit malfunction.

P0371 identifies an excessive high-resolution timing pulse count.

The High-Resolution Signal A source may be related to crankshaft position on some vehicles, but it may originate from a completely different component, including an optical sensor inside a diesel injection pump.

Replacing the crankshaft sensor without identifying the P0371 signal source is guessing with an invoice attached.

P0371 vs P0321

P0321 identifies an engine-speed input range or performance problem.

P0371 concerns the number of pulses in a specific high-resolution timing signal.

The PCM may display reasonable engine RPM while still detecting extra high-resolution timing pulses.

How to Diagnose the P0371 Code

Diagnosing P0371 may require:

1. Scan all control modules

Record stored, pending and permanent codes before clearing them.

Look for:

Save the freeze-frame data, including:

The conditions under which P0371 sets may reveal whether the excessive pulses appear during cranking, idle or higher engine speed.

2. Identify the Signal A source

Use factory information to determine:

Do not assume P0371 refers to a conventional crankshaft sensor.

3. Check battery and charging voltage

Verify:

Alternator ripple or unstable system voltage can introduce electrical noise into sensitive timing circuits.

4. Inspect the connector

With the ignition off, inspect:

Poor terminal contact can create rapid signal transitions that the PCM interprets as extra pulses.

5. Inspect the wiring harness

Follow the Signal A circuit from the sensor to the PCM.

Look for:

High-resolution timing signals are sensitive to electromagnetic interference. Routing and shielding matter.

6. Check sensor supply voltage

For a powered sensor, verify the correct supply voltage.

Depending on the system, this may be:

Monitor the supply with a graphing meter or oscilloscope.

Look for:

7. Test the sensor ground

Perform a voltage-drop test while the engine runs.

A poor ground may cause the signal reference point to move, producing false threshold crossings.

Inspect:

8. Inspect the waveform

Use an oscilloscope to view Signal A.

A healthy waveform should normally show:

A P0371 waveform may show:

A digital multimeter may display an average voltage that looks normal while completely hiding the extra pulses.

9. Count pulses during a known timing window

Use the oscilloscope’s pulse-count or measurement function when available.

Compare:

Determine whether the PCM is receiving:

10. Compare Signal A with the low-resolution reference

Some systems generate both high- and low-resolution signals.

Use a dual-channel oscilloscope to compare:

If the low-resolution reference remains normal while Signal A produces extra pulses, focus on the high-resolution sensor channel, encoder track and wiring.

11. Check for electrical interference

Test the waveform while operating:

Temporarily isolate nonessential aftermarket equipment according to safe procedures.

Look for noise caused by:

12. Perform a wiggle test

Monitor the waveform while gently moving:

If extra pulses appear during movement, inspect terminal tension and conductor integrity.

13. Test the sensor hot and cold

Monitor pulse count during:

A sensor may double-trigger only after its internal electronics become hot.

If power, ground and wiring remain stable while false pulses appear, sensor replacement may be justified.

14. Inspect sensor air gap

On magnetic and Hall-effect applications, verify the sensor air gap.

An incorrect or changing gap may cause:

Check for:

15. Inspect the encoder or reluctor

Where permitted, inspect for:

A cracked optical disc may produce additional light transitions as the damaged area passes the sensor.

Do not open a calibrated diesel injection pump unless the service procedure specifically allows it.

16. Confirm replacement-part compatibility

If P0371 appeared after repairs, confirm:

A component can physically fit while producing a pulse pattern the PCM does not recognize.

17. Verify mechanical timing

Inspect mechanical timing if P0371 appears with:

Possible faults include:

18. Evaluate the PCM last

Before replacing the PCM, verify:

A PCM input fault is possible, but sensor, encoder and wiring problems are more common.

Common P0371 Diagnostic Mistakes

Replacing the crankshaft sensor automatically

The high-resolution signal may come from an injection-pump optical sensor or distributor pickup.

Diagnosing P0371 with only a multimeter

A meter may show normal average voltage while an oscilloscope reveals dozens of false signal edges.

Replacing the injection pump without checking wiring noise

Damaged shielding or alternator interference can imitate an internal pump fault.

Ignoring the encoder

A new sensor cannot correct a cracked disc or incorrect trigger pattern.

Assuming more pulses mean the engine is turning faster

The PCM compares pulse count with other speed references. P0371 means the signal contains events the PCM considers invalid.

Overlooking recent repairs

An incorrect sensor, trigger wheel, pump or calibration may produce the wrong pulse count immediately after installation.

Ignoring aftermarket electronics

Poorly routed or grounded accessories can inject noise into sensitive timing circuits. The subwoofer may be innocent, but its wiring occasionally has ambitions.

How to Fix the P0371 Code

The correct repair depends on testing.

Possible repairs include:

Estimated P0371 Repair Costs

RepairEstimated cost
Diagnostic inspection$120–$325
Connector or terminal repair$100–$400
Signal-wire or shielding repair$150–$900
Crankshaft or camshaft sensor replacement$150–$650
Optical timing sensor replacement$300–$1,500
Alternator replacement$400–$1,200
Encoder or reluctor repair$500–$2,500+
Injection-pump repair or replacement$1,000–$4,500+
PCM programming or replacement$300–$2,500+

Actual costs depend on the vehicle and the source of High-Resolution Signal A.

Can You Drive with the P0371 Code?

Driving is not recommended if the engine stalls, misfires, smokes heavily or loses power.

A short trip may be possible when:

Stop driving if:

How to Verify the Repair

After completing the repair:

  1. Clear all trouble codes.
  2. Monitor Signal A status.
  3. Record the high-resolution waveform.
  4. Count pulses during the specified timing window.
  5. Compare Signal A with the low-resolution reference.
  6. Test with electrical accessories operating.
  7. Perform a cold start.
  8. Perform a hot restart.
  9. Road-test under the freeze-frame conditions.
  10. Rescan for pending P0370–P0374 codes.
  11. Complete any required relearn.
  12. Confirm readiness monitors complete.

Frequently Asked Questions

What does the P0371 code mean?

P0371 means the PCM detected more High-Resolution Signal A pulses than expected.

Does P0371 mean the crankshaft sensor is bad?

Not necessarily. Signal A may come from an optical injection-pump sensor, distributor pickup or another timing sensor.

What causes extra timing pulses?

Common causes include electrical noise, double-triggering, a damaged encoder, incorrect air gap or an incompatible sensor.

Can alternator problems cause P0371?

Yes. Excessive alternator ripple or poor grounding may introduce noise into the timing-signal circuit.

Can a cracked encoder disc cause P0371?

Yes. A cracked or wobbling optical encoder can create additional light transitions that appear as extra pulses.

Is P0371 commonly found on diesel engines?

It may appear on diesel systems using an optical injection-pump timing sensor, but the signal source is manufacturer-specific.

Can P0371 cause a no-start condition?

Yes. The PCM may be unable to calculate correct injection or ignition timing when the pulse count is invalid.

What is the difference between P0370 and P0371?

P0370 is a general high-resolution signal malfunction. P0371 specifically means too many pulses were detected.

Can an incorrect replacement sensor cause P0371?

Yes. A sensor or encoder with the wrong output pattern may generate more pulses than the PCM expects.

Do I need an oscilloscope to diagnose P0371?

An oscilloscope is strongly recommended because a multimeter cannot display false edges, pulse spacing or excessive pulse count.

Final Thoughts

P0371 means the PCM counted more High-Resolution Signal A pulses than the engine-management strategy allows.

Begin by identifying the Signal A source. Inspect its connector, wiring, power, ground and shielding. Then use an oscilloscope to determine whether the additional pulses come from electrical noise, sensor double-triggering or a damaged encoder.

Do not replace the injection pump or crankshaft sensor until the waveform identifies the guilty component. Extra pulses are evidence—and the scope is how you catch them lying.

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