The P0370 OBD-II trouble code means the powertrain control module has detected a malfunction in the Timing Reference High-Resolution Signal “A” circuit.
This high-resolution pulse signal helps the PCM determine precise engine position, speed and fuel-injection or ignition timing. Depending on the vehicle, Signal A may originate from an optical sensor inside a diesel injection pump, a distributor-mounted sensor, a crankshaft or camshaft pickup, or another manufacturer-specific engine-position sensor.
P0370 does not automatically identify a failed crankshaft position sensor. The signal’s source and circuit design must be confirmed through vehicle-specific service information before testing or replacing components.
P0370 Code Quick Reference
| Item | Details |
|---|---|
| Code | P0370 |
| Definition | Timing Reference High-Resolution Signal “A” Malfunction |
| System | Engine-position and timing reference |
| Fault type | General high-resolution signal malfunction |
| Common applications | Diesel and manufacturer-specific ignition systems |
| Common symptoms | Hard starting, stalling, misfires and reduced power |
| Common causes | Sensor failure, damaged wiring or defective encoder |
| Repair urgency | High |
| Safe to drive? | Limited driving only if the engine runs normally |
What Does the P0370 Code Mean?
The PCM needs accurate engine-position information to control fuel injection and ignition timing.
Basic engine-speed information tells the PCM how fast the crankshaft is rotating. A high-resolution timing signal provides a much more detailed pulse pattern that allows the PCM to identify precise rotational position.
The PCM may use this signal to control:
- Fuel-injection timing
- Injector sequencing
- Ignition timing
- Engine-speed calculation
- Cylinder identification
- Misfire detection
- Injection-pump operation
- Variable timing strategies
- Engine startup synchronization
P0370 is stored when the PCM detects a general malfunction in the High-Resolution Signal A circuit.
Depending on the manufacturer’s strategy, the PCM may recognize:
- An invalid pulse pattern
- Incorrect signal frequency
- Missing groups of pulses
- Distorted waveform
- Signal voltage outside the expected range
- Incorrect relationship to another timing reference
- Sensor circuit open or shorted
- A signal that does not match engine speed
- An internal sensor or encoder failure
P0370 is the broad malfunction code for this signal family. Related P0371–P0374 codes describe more specific pulse-count or signal-loss conditions.
What Is a High-Resolution Timing Signal?
A high-resolution timing signal is a rapid series of electrical pulses produced as an encoder wheel, reluctor, shutter wheel or optical disc rotates past a sensor.
More pulses per revolution provide the PCM with more precise position information.
A simplified system may work like this:
- The engine or injection pump rotates.
- An encoder wheel passes through or near a sensor.
- The sensor generates a series of electrical pulses.
- The PCM counts and measures those pulses.
- The PCM determines precise engine position and speed.
- Fuel injection or ignition events are commanded at the correct moment.
A low-resolution reference may tell the PCM when a major timing event occurs. The high-resolution signal fills in the smaller divisions between those events.
It is the difference between knowing which block you are on and knowing the exact driveway. Engines, being mildly demanding pieces of machinery, prefer the driveway.
What Does Signal “A” Mean?
Signal A identifies the first or primary high-resolution timing-reference circuit used by the vehicle.
It does not always mean:
- Crankshaft Position Sensor A
- Camshaft Position Sensor A
- Bank 1
- Intake camshaft
- The first sensor physically visible
The exact Signal A source varies by manufacturer and engine design.
Possible sources include:
- Optical sensor inside a diesel injection pump
- Fuel-pump timing sensor
- Distributor optical pickup
- Crankshaft position sensor
- Camshaft position sensor
- Dedicated engine timing sensor
- Encoder or pulse-generator assembly
Consult the wiring diagram and trouble-code diagnostic chart for the specific vehicle.
Where Is the P0370 Sensor Located?
There is no universal P0370 sensor location.
Depending on the application, the signal source may be found:
- Inside or on the fuel-injection pump
- Inside the distributor
- Near the crankshaft pulley
- Beside the flywheel or flexplate
- At the rear of the engine block
- Near a camshaft sprocket
- Inside a timing cover
- Integrated into another position-sensor assembly
Some diesel applications use an optical sensor that reads slots in a rotating encoder disc inside the injection pump. Contaminated fuel, internal pump debris or optical-sensor failure can interfere with the pulse pattern.
Other vehicles generate the timing reference through a crankshaft, camshaft or distributor-mounted pickup.
Identifying the exact system comes before diagnosis. Otherwise, P0370 can turn into a very expensive tour of every position sensor on the engine.
How an Optical Timing Sensor Works
Optical timing sensors commonly contain:
- Light-emitting source
- Light-sensitive receiver
- Rotating slotted encoder disc
- Power circuit
- Ground circuit
- High-resolution signal circuit
- Low-resolution or reference signal on some systems
As the encoder rotates, its slots alternately allow and block light. The receiver converts those changes into electrical pulses.
The PCM expects:
- A specific number of pulses per revolution
- Consistent pulse spacing
- Clean high-to-low transitions
- Stable signal voltage
- Correct synchronization with other timing inputs
Contamination, damaged encoder slots, internal pump wear or electrical failure can disturb the waveform and trigger P0370.
P0370 Symptoms
Possible symptoms include:
- Illuminated check engine light
- Extended cranking
- Hard starting
- Intermittent no-start
- Engine stalling
- Rough idle
- Engine misfires
- Hesitation
- Reduced acceleration
- Reduced engine power
- Poor fuel economy
- Excessive exhaust smoke on diesel applications
- Unstable injection timing
- Surging
- Engine cutting out
- Reduced-power or limp mode
- Engine running normally despite the stored code
Symptoms depend on whether the PCM can substitute another position signal.
Some vehicles may continue running with reduced timing precision. Others may stall or refuse to start because the PCM cannot determine when to operate the injectors or ignition system.
Common Causes of P0370
Possible causes include:
- Failed high-resolution timing sensor
- Failed optical sensor
- Defective injection-pump timing sensor
- Damaged crankshaft or camshaft position sensor
- Damaged distributor pickup
- Open signal circuit
- Signal wire shorted to ground
- Signal wire shorted to voltage
- Missing sensor supply voltage
- Poor sensor ground
- Loose sensor connector
- Corroded connector terminals
- Bent or pushed-back terminals
- Water or oil intrusion
- Fuel contamination affecting an optical sensor
- Damaged encoder disc
- Cracked or loose reluctor wheel
- Missing or damaged trigger teeth
- Excessive sensor air gap
- Metal debris attached to a magnetic sensor
- Harness damage near the injection pump
- Wiring routed near high-current circuits
- Damaged signal shielding
- Electrical interference
- Low cranking voltage
- Weak battery
- Poor engine or PCM grounds
- Mechanical timing problem
- Incorrect replacement sensor
- PCM input-circuit failure
- Outdated or incorrect PCM calibration
How Serious Is the P0370 Code?
P0370 should be treated as a high-priority code because the timing reference can directly affect starting, injection and ignition operation.
Possible consequences include:
- Unexpected engine stalling
- No-start condition
- Incorrect fuel-injection timing
- Engine misfires
- Reduced power
- Excessive diesel smoke
- Increased emissions
- Poor fuel economy
- Catalytic-converter or diesel aftertreatment damage
- Damage caused by incorrect injection timing
- Vehicle entering limp mode
Stop driving if:
- The engine stalls
- The engine is difficult to restart
- The check engine light flashes
- Heavy smoke develops
- Power drops suddenly
- The engine runs severely rough
- Injection-pump or timing-system damage is suspected
P0370 vs P0335
P0335 identifies a Crankshaft Position Sensor A circuit malfunction.
P0370 identifies a malfunction in the high-resolution Timing Reference Signal A.
| Code | Diagnostic focus |
| P0335 | Crankshaft Position Sensor A circuit |
| P0370 | High-resolution timing pulse signal |
On some vehicles, both signals may originate from related engine-position hardware. On others, P0370 comes from an optical sensor inside the injection pump and has little to do with the conventional crankshaft sensor.
Do not replace the crankshaft sensor solely because P0370 contains the words “timing reference.”
P0370 vs P0322
P0322 means the PCM detected no ignition or distributor engine-speed input signal.
P0370 concerns the high-resolution timing-reference pulse train.
The difference is:
- P0322: The PCM loses the general engine-speed input.
- P0370: The PCM detects a malfunction in the more detailed timing-reference signal.
The engine-speed input may remain present while the high-resolution pulse pattern is invalid.
P0370 vs P0323
P0323 identifies an intermittent ignition or distributor engine-speed input.
P0370 is not specifically an intermittent code. It is the general malfunction code for High-Resolution Signal A.
P0373 is the more specific intermittent or erratic high-resolution signal code in the P0370 family.
P0370 vs P0315
P0315 means the crankshaft-position variation value has not been learned.
P0370 indicates an actual timing-reference signal malfunction.
A relearn procedure will not repair:
- Broken wiring
- Failed optical sensor
- Damaged encoder disc
- Missing sensor power
- Poor sensor ground
- Defective injection-pump electronics
Perform a relearn only when the manufacturer requires it and the signal circuit is working correctly.
P0370 vs P0371, P0372, P0373 and P0374
These codes monitor the same high-resolution Timing Reference Signal A but identify different failure patterns.
| Code | Meaning |
| P0370 | General Signal A malfunction |
| P0371 | Too many pulses |
| P0372 | Too few pulses |
| P0373 | Intermittent or erratic pulses |
| P0374 | No pulses detected |
This distinction creates a clean diagnostic cluster:
- P0370 owns the general circuit and waveform malfunction.
- P0371 owns excessive pulse count.
- P0372 owns insufficient pulse count.
- P0373 owns intermittent pulse loss.
- P0374 owns complete absence of pulses.
How to Diagnose the P0370 Code
Diagnosing P0370 may require:
- Professional scan tool
- Digital multimeter
- Oscilloscope
- Vehicle-specific wiring diagram
- Back-probe leads
- Manufacturer service information
- Fuel-system equipment on diesel applications
Do not open or disassemble a high-pressure diesel injection pump unless the repair procedure specifically permits it. Internal service may require a clean environment, specialized calibration equipment and professional rebuilding.
1. Scan all control modules
Record every stored, pending and permanent code before clearing anything.
Look for:
- P0371–P0374
- P0335–P0339
- P0321–P0323
- Camshaft-position codes
- Injection-pump codes
- Fuel-pressure codes
- Low-voltage codes
- Module communication faults
Save the freeze-frame data, including:
- Engine speed
- Battery voltage
- Coolant temperature
- Vehicle speed
- Engine load
- Fuel pressure
- Injection timing
- Time since startup
Companion codes may reveal whether the problem affects one timing signal or the entire engine-management system.
2. Identify the High-Resolution Signal A source
Use factory service information to determine:
- Which sensor generates Signal A
- Where the sensor is located
- Whether the sensor is optical, Hall-effect or magnetic
- Whether it is integrated into the injection pump
- Which PCM terminal receives the signal
- Whether the circuit shares power or ground
- The expected pulse count and waveform
This is the most important step in diagnosing P0370.
P0370 does not guarantee that the vehicle uses the same sensor arrangement described by a generic scan-tool definition.
3. Inspect the battery and charging system
Verify:
- Battery state of charge
- Battery terminal condition
- Cranking voltage
- Charging voltage
- Engine ground straps
- PCM powers and grounds
Low cranking voltage may weaken a magnetic-sensor signal or interrupt operation of an optical sensor.
Correct electrical-system faults before evaluating the timing waveform.
4. Inspect the connector and harness
With the ignition off, inspect:
- Loose connector
- Broken locking tab
- Corroded terminals
- Bent or recessed pins
- Water intrusion
- Oil or fuel contamination
- Brittle insulation
- Wiring chafed against brackets
- Harness damage near the injection pump
- Wiring stretched during previous repairs
- Improper aftermarket splices
Injection-pump harnesses operate in a hot, vibration-heavy environment. Connector and wiring faults are common enough to deserve inspection before the pump receives a death sentence.
5. Identify the sensor circuit design
Determine whether the signal source uses:
- A powered Hall-effect sensor
- An optical sensor
- A two-wire magnetic pickup
- A distributor reference sensor
- An integrated pump-control module
- Another manufacturer-specific circuit
The test method and expected voltage depend on the design.
6. Check sensor supply voltage
For a powered sensor, verify supply voltage at the connector.
The expected value may be:
- Approximately 5 volts
- Battery voltage
- Another manufacturer-specified supply
If voltage is missing, inspect:
- Fuse
- Relay
- Shared sensor supply
- Open power wire
- Shorted sensor
- PCM supply circuit
A shorted sensor on a shared reference circuit can pull down power to several sensors.
7. Check the sensor ground
Perform a voltage-drop test between the sensor ground and battery negative while the circuit operates.
A continuity test may show an apparently good ground that fails under load.
Inspect:
- Sensor ground wire
- Ground splice
- PCM ground
- Engine ground straps
- Corrosion beneath ground fasteners
8. Test the Signal A circuit
Check the signal wire for:
- Open circuit
- Short to ground
- Short to voltage
- Excessive resistance
- Intermittent connection
- Cross-contact with another signal
- Damaged shielding
Disconnect the PCM and sensor when required before performing resistance tests.
Move the harness while monitoring the circuit to locate hidden conductor breaks.
9. Observe engine-speed and synchronization data
Use a scan tool while cranking.
Check whether the PCM displays:
- Engine RPM
- Camshaft synchronization
- Injection-pump timing
- High-resolution signal status
- Fuel-injection command
- Crank request or start authorization
If RPM remains at zero, a more general crankshaft or engine-speed input fault may be present.
If RPM is available but the high-resolution timing status fails, focus on the Signal A source and circuit.
10. Inspect the waveform
An oscilloscope is the preferred tool for P0370 diagnosis.
A healthy high-resolution waveform should generally show:
- Consistent pulse amplitude
- Even pulse spacing
- Clean transitions
- Correct pulse count
- No unexplained gaps
- Stable relationship to the low-resolution reference
Look for:
- Missing pulse groups
- Unequal pulse spacing
- Weak amplitude
- Rounded transitions
- Electrical noise
- Signal stuck high or low
- Incorrect frequency
- Waveform changing with temperature
- Pattern inconsistent with engine speed
Compare the signal with a known-good waveform for the exact engine.
11. Compare high- and low-resolution signals
Some systems produce both high- and low-resolution reference signals.
Use a dual-channel oscilloscope to compare:
- Signal timing
- Pulse alignment
- Missing sections
- Relative phase
- Encoder indexing
- Signal amplitude
A normal low-resolution reference with a corrupted high-resolution pattern may point toward:
- Damaged encoder track
- Optical contamination
- Failed high-resolution sensor channel
- Signal-wire problem
12. Perform a wiggle test
While monitoring the waveform, gently move:
- Sensor connector
- Injection-pump harness
- Harness bends
- Wiring near the engine
- PCM connector
If the signal changes, isolate the affected section.
Do not pull hard enough to create a new open circuit. The original problem has already volunteered.
13. Test the sensor hot and cold
Monitor the waveform during:
- Cold startup
- Warm idle
- Hot restart
- Heat soak
- Increased engine speed
An optical or Hall-effect sensor may fail only after internal electronics become hot.
If power and ground remain stable while the signal collapses, the sensor or integrated module becomes more suspect.
14. Inspect the encoder or trigger wheel
Where service procedures allow, inspect for:
- Cracked encoder disc
- Damaged slots
- Missing trigger teeth
- Loose reluctor wheel
- Contamination
- Metal debris
- Incorrect sensor air gap
- Excessive shaft movement
- Internal pump wear
Avoid opening a diesel injection pump outside a properly equipped environment. A contaminated injection system can quickly turn a diagnostic repair into an expensive fuel-system rebuild.
15. Check fuel condition on optical-pump systems
Some diesel optical-sensor systems may be affected by:
- Contaminated fuel
- Water in fuel
- Internal pump debris
- Incorrect fuel
- Aerated fuel
- Internal pump wear
Follow the manufacturer’s testing procedure before condemning the optical sensor or complete pump assembly.
16. Verify mechanical timing
Mechanical timing should be inspected when P0370 appears with:
- Crankshaft-to-camshaft correlation codes
- Injection-timing codes
- Abnormal engine noise
- Low compression
- Recent timing-system repairs
- Incorrect waveform alignment
Possible causes include:
- Jumped timing belt
- Stretched timing chain
- Loose timing gear
- Incorrect injection-pump timing
- Damaged drive components
17. Evaluate the PCM last
Before replacing the PCM, verify:
- Correct signal source
- Stable sensor power and ground
- Signal-wire integrity
- Correct waveform at the sensor
- Correct waveform at the PCM
- Proper encoder condition
- Mechanical timing
- PCM powers and grounds
- Applicable software updates
A PCM failure is possible, but wiring, sensor and encoder problems are considerably more common.
Common P0370 Diagnostic Mistakes
Replacing the crankshaft sensor automatically
P0370 may use a completely different signal source, particularly on diesel injection-pump systems.
Ignoring vehicle-specific service information
The generic code definition does not identify the sensor location or circuit design.
Replacing the injection pump without waveform testing
A damaged connector or signal wire can imitate an internal pump failure.
Performing only a resistance test
A sensor may pass a static resistance test and still produce a distorted or incomplete pulse pattern.
Skipping battery testing
Low cranking voltage can interfere with high-resolution timing signals.
Confusing P0370 with P0315
P0315 indicates that a variation value has not been learned. P0370 identifies an actual signal malfunction.
Opening a diesel injection pump unnecessarily
Internal pump service requires cleanliness, calibration equipment and application-specific training. Curiosity becomes expensive surprisingly quickly around high-pressure diesel components.
How to Fix the P0370 Code
The correct repair depends on the diagnosed cause.
Possible repairs include:
- Reconnecting the timing-sensor connector
- Repairing loose or damaged terminals
- Cleaning approved connector contamination
- Repairing damaged wiring
- Restoring sensor power
- Repairing the sensor ground
- Correcting a signal-wire short
- Restoring signal shielding
- Replacing the high-resolution timing sensor
- Replacing an optical sensor assembly
- Repairing a distributor pickup
- Replacing a damaged crankshaft or camshaft sensor
- Replacing a damaged encoder disc or reluctor
- Correcting sensor air gap
- Repairing injection-pump wiring
- Professionally rebuilding or replacing the injection pump
- Correcting mechanical timing
- Replacing a weak battery
- Repairing engine or PCM grounds
- Updating PCM software
- Repairing or replacing the PCM after complete testing
Estimated P0370 Repair Costs
| Repair | Estimated cost |
| Diagnostic inspection | $120–$300 |
| Connector or terminal repair | $100–$400 |
| Wiring-harness repair | $150–$800 |
| Crankshaft or camshaft sensor replacement | $150–$650 |
| Distributor pickup replacement | $200–$800 |
| Optical timing sensor repair | $300–$1,500 |
| Injection-pump repair or replacement | $1,000–$4,500+ |
| Timing-belt or timing-chain repair | $800–$4,000+ |
| PCM replacement and programming | $800–$2,500+ |
Costs vary substantially because the Signal A source differs between vehicles.
Can You Drive with the P0370 Code?
Driving with P0370 is not recommended if the engine stalls, misfires, smokes excessively or becomes difficult to start.
A short trip may be possible when:
- The engine runs smoothly
- The check engine light remains steady
- No stalling has occurred
- Power remains predictable
- No excessive smoke is present
Stop driving if:
- The engine stalls
- The vehicle enters limp mode
- The check engine light flashes
- Injection timing becomes unstable
- Heavy smoke develops
- The engine will not restart reliably
How to Verify the Repair
After completing the repair:
- Clear all diagnostic codes.
- Monitor engine RPM during cranking.
- Verify timing synchronization.
- Observe the high-resolution waveform.
- Compare high- and low-resolution signals when applicable.
- Perform a cold start.
- Allow the engine to reach operating temperature.
- Perform a hot restart.
- Road-test under the freeze-frame conditions.
- Rescan for pending P0370–P0374 codes.
- Complete any required relearn procedure.
- Confirm readiness monitors complete.
Frequently Asked Questions
What does the P0370 code mean?
P0370 means the PCM detected a malfunction in the Timing Reference High-Resolution Signal A circuit.
Is P0370 a crankshaft sensor code?
Not necessarily. The signal may originate from an optical injection-pump sensor, distributor pickup or another engine-position sensor.
Is P0370 commonly associated with diesel engines?
It can appear on diesel applications using injection-pump timing or optical sensors, but the exact system is manufacturer-specific.
Can P0370 cause a no-start condition?
Yes. The PCM may be unable to determine precise injection or ignition timing without the high-resolution signal.
Can a weak battery cause P0370?
Low cranking voltage can weaken sensor output or interrupt powered sensor operation.
Can contaminated diesel fuel cause P0370?
On systems using an optical sensor inside the injection pump, fuel contamination or internal pump debris may interfere with sensor operation.
What is the difference between P0370 and P0374?
P0370 is a general high-resolution signal malfunction. P0374 means the PCM detects no pulses from Signal A.
Can clearing P0370 fix the problem?
No. Clearing the code only removes the warning until the signal malfunction occurs again.
Does P0370 mean the injection pump is bad?
Not automatically. Wiring, connectors, sensor power, grounds and external signal circuits must be tested first.
Do I need an oscilloscope to diagnose P0370?
Not always, but an oscilloscope is the best tool for evaluating pulse count, spacing, amplitude and waveform integrity.
Final Thoughts
P0370 means the PCM cannot rely on Timing Reference High-Resolution Signal A.
The first diagnostic step is identifying where that signal originates on the specific vehicle. It may come from an injection-pump optical sensor, distributor pickup, crankshaft sensor, camshaft sensor or dedicated timing reference.
Once the source is confirmed, inspect its connector and wiring, verify power and ground, and examine the waveform before replacing expensive components.
The code says “high-resolution timing signal,” not “buy every position sensor listed by the parts store.” The wiring diagram remains cheaper and considerably less judgmental.
