Fuel Delivery

Gold ChapterATLAS-FUELDELI-0244Template 2.2

P0370

Timing Reference High Resolution Signal A Malfunction

P0370 — Timing Reference High Resolution Signal A Malfunction — applies to Engine Timing Reference Sensing and identifies circuit malfunction. The monitored item is Timing Reference High Resolution Signal A circuit. The code wording describes the failed monitor and does not automatically…

SeverityMedium to high
DriveabilityLimit driving if there is hard starting, stalling, loss of synchronization, or sudden power loss. An intermittent timing-reference fault can stop the engine.
Diagnostic Time1.0-3.0 hours
Typical Cost$50-$3,500+ depending on proven cause and vehicle
Atlas StatusGold Chapter
Reviewed2026-08

Diagnostic Snapshot

Most Common Cause: reference-sensor connector/harness faultEngine Damage Risk: Low directly, but a related mechanical timing or reluctor fault can carry significant engine-damage risk on some engines.Safe to Drive: Limit driving if there is hard starting, stalling, loss of synchronization, or sudden power loss. An intermittent timing-reference fault can stop the engine.Professional Scan Tool: Recommended; strongly recommended for Gold-tier waveform, EVAP monitor, and range/performance diagnosisMechanical Test Recommended: Yes when scan/circuit results indicate ignition secondary, timing reference, glow load, EVAP sealing/flow, or sender/float concernsDIY Difficulty: Advanced DIY / Professional preferred

Atlas Academy

Learn the System

Before diagnosing this code, it helps to understand the system behind it.

Read Understanding Fuel Delivery Systems

Technical Summary

P0370 — Timing Reference High Resolution Signal A Malfunction — is a Gold-tier chapter covering Timing Reference High Resolution Signal A circuit. The exact monitored fault is circuit malfunction.

The PCM evaluates the high-resolution timing reference Signal A for valid pulse count, frequency, continuity, and synchronization needed for precise engine position calculation. Freeze-frame matters because the test may depend on system voltage, temperature, fuel level, run time, load, and related sensor validity.

Start with proof: Identify what the manufacturer calls high resolution signal a and scope it together with the related crank/cam/reference signal. Then use the correct wiring diagram, graphing data, and an independent waveform/current, smoke/leak, or physical test.

Do not invent universal voltage, resistance, current, pressure, leak-rate, or waveform specifications. Circuit architecture and monitor thresholds vary; manufacturer service data takes priority.

Safety/driveability: Limit driving if there is hard starting, stalling, loss of synchronization, or sudden power loss. An intermittent timing-reference fault can stop the engine. Risk if ignored: Low directly, but a related mechanical timing or reluctor fault can carry significant engine-damage risk on some engines.

What You'll Learn

  • Exact meaning of P0370
  • Monitor/enabling-condition logic
  • Freeze-frame and live-data clues
  • Electrical versus physical test direction
  • Repair/monitor verification

Think Like a Technician

Treat P0370 as evidence, not a parts order. The PCM is evaluating the high-resolution timing reference Signal A for valid pulse count, frequency, continuity, and synchronization needed for precise engine position calculation.

Prove command/input first, then circuit integrity, then physical action, then feedback. The first broken link is the diagnostic target.

What This Code Means

P0370 — Timing Reference High Resolution Signal A Malfunction — applies to Engine Timing Reference Sensing and identifies circuit malfunction. The monitored item is Timing Reference High Resolution Signal A circuit. The code wording describes the failed monitor and does not automatically condemn the named part.

The PCM evaluates the high-resolution timing reference Signal A for valid pulse count, frequency, continuity, and synchronization needed for precise engine position calculation. Enabling conditions vary and can depend on voltage, temperature, fuel level, engine run time, load, related-sensor validity, and whether prerequisite monitors have completed.

Start with proof: Identify what the manufacturer calls high resolution signal a and scope it together with the related crank/cam/reference signal. Then use the exact circuit design plus waveform/current, smoke/leak, or physical-system testing appropriate to the fault.

Gold-level diagnosis emphasizes monitor behavior and system relationships: compare command to electrical response, electrical response to physical action, and physical action to the feedback the PCM uses to decide whether the test passed.

System Overview

Engine Timing Reference Sensing provides electrical commands or feedback used by the PCM to control combustion, starting, emissions, and fuel information. Diagnose command/input, circuit integrity, physical response, and feedback as separate links.

Why This Code Sets

The monitor for P0370 runs only when the PCM has enough valid information to judge Timing Reference High Resolution Signal A circuit or the related system response.

Once enabled, the PCM evaluates the high-resolution timing reference Signal A for valid pulse count, frequency, continuity, and synchronization needed for precise engine position calculation. P0370 is stored when the result remains outside the calibrated expectation through the required samples or test interval.

The wording—circuit malfunction—determines test priority. High/low/circuit faults favor electrical testing; range/performance and leak faults require proving whether the feedback is wrong or the physical system truly failed its target.

Common Symptoms

  • Check Engine Light
  • Possible emissions-test failure
  • Hard start or no-start
  • Intermittent stall
  • Extended cranking
  • Possible loss of power

Most Likely Causes

  • 1. reference-sensor connector/harness fault
  • 2. sensor power/ground problem where applicable
  • 3. damaged optical/reluctor/tone pattern
  • 4. sensor internal failure
  • 5. incorrect air gap/alignment
  • 6. timing drive or distributor/injection-pump issue where applicable
  • 7. module input fault

Common Vehicles

Generic OBD-II code used across many makes; exact applications, component naming, circuit strategy, EVAP architecture, sender design, and monitor thresholds vary. Verify the specific VIN.

Freeze Frame Clues

  • System/cranking voltage
  • RPM/load/vehicle speed
  • ECT/IAT and time since start
  • Fuel level and recent refueling when relevant
  • Key Engine Timing Reference Sensing command/feedback PIDs
  • Misfire or synchronization data where relevant
  • Ambient/hot-soak/cold-start context

Live Data Expectations

Monitor RPM, synchronization/reference status, injection/ignition timing data, and any manufacturer-specific high-resolution signal PID while scoping the reference waveform. Missing or irregular high-resolution pulses with a stable low-resolution reference strongly localize the fault.

Typical Verification Tests

  • Confirm P0370 absent from current/pending memory
  • Recreate freeze-frame operating condition
  • Graph/scope affected signal or command
  • Repeat heat/wiggle/cold-soak/refueling test if intermittent
  • Perform smoke/current/flow test where appropriate
  • Perform required relearn
  • Complete applicable readiness monitor
  • Confirm original complaint is resolved

Before You Condemn

  • Confirm VIN-specific definition/component identity
  • Save freeze-frame/pending/related codes
  • Verify system voltage and grounds
  • Inspect connector/terminal fit
  • Compare scan data with waveform/current/leak/physical test
  • Run OEM circuit/functional test
  • Rule out mechanical/flow/sealing causes
  • Document the failed test

Before Replacing Parts

Save freeze-frame and verify the exact component/system. Identify what the manufacturer calls high resolution signal a and scope it together with the related crank/cam/reference signal. Replace parts only after a failed circuit, waveform/current, leak, flow, sender, or OEM functional test is documented.

Diagnostic Workflow

  1. Confirm P0370 and save current, pending, and history DTCs before clearing anything.
  2. Save freeze-frame and related codes. Record RPM/load, ECT/IAT, system voltage, fuel level, misfire data, and system-specific command/feedback PIDs.
  3. Verify the VIN-specific code definition, component assignment, circuit design, monitor prerequisites, and service precautions.
  4. Inspect Timing Reference High Resolution Signal A circuit connector/harness for corrosion, terminal tension, heat damage, fluid intrusion, chafing, and previous repairs.
  5. Verify battery and charging-system voltage are stable; weak voltage can distort coil, sensor, glow, EVAP, and sender diagnostics.
  6. Identify what the manufacturer calls high resolution signal a and scope it together with the related crank/cam/reference signal.
  7. Identify sensor/reference technology and required supply/ground or magnetic pickup test method.
  8. Scope the affected signal during crank and idle; inspect amplitude, frequency/duty, missing pulses, noise, and dropout.
  9. Scope the related crank/cam/reference signal simultaneously to evaluate synchronization and phase.
  10. Test sensor power, ground, and signal circuits under operating conditions; load-test wiring where appropriate.
  11. Wiggle the harness near engine movement/heat points while monitoring waveform and sync status.
  12. Inspect sensor mounting, air gap, reluctor/tone/optical pattern, and mechanical indexing where serviceable.
  13. If waveform is clean but phase/reference is wrong, verify mechanical timing, VVT parked position, distributor/injection-pump indexing, or reluctor location as applicable.
  14. Repair the proven sensor, wiring, reluctor/reference source, or mechanical timing cause and perform required relearn.
  15. Verify hot/cold starting, stable synchronization, and no current/pending P0370.

Labor & Inspection Checklist

  • Verify VIN/engine/service information
  • Scan all modules/save freeze-frame
  • Inspect component/connector/harness
  • Check ignition/timing/glow/EVAP/fuel-sender basics
  • Perform circuit test
  • Compare live data with independent physical test
  • Repair/relearn
  • Complete monitor verification

Common Repairs

  • Repair proven connector/wiring/power/ground fault
  • Replace Timing Reference High Resolution Signal A circuit only after test failure is proven
  • Correct verified ignition/timing/glow/EVAP/fuel-sender mechanical cause
  • Perform required relearn or monitor procedure
  • Verify no current or pending DTC

Common Parts

  • Connector pigtail
  • Harness repair materials
  • Sensor/coil/solenoid only if proven
  • Seals/hoses/sender/control parts only after diagnosis

Shop Notes

Monitor logic for P0370: verify the enabling conditions were satisfied before interpreting the DTC. Voltage, temperature, fuel level, engine state, and prerequisite sensor validity can determine whether the test runs.

Electrical proof for P0370: inspect terminal fit and test the circuit in its loaded operating state. Continuity or unplugged voltage alone can miss high resistance, a weak terminal, or a driver that fails only under current.

Physical proof for P0370: if the electrical path is credible, verify the physical result—spark energy, timing-reference integrity, glow current, valve flow/sealing, EVAP leak rate, or sender/float movement.

Intermittent strategy for P0370: reproduce heat, vibration, cold soak, refueling, tank movement, or engine load while recording the relevant signal. Save the trace for direct pre/post-repair comparison.

Related-code strategy for P0370: misfire, crank/cam, system-voltage, EVAP pressure, purge/vent, or fuel-level codes can expose a common cause. Use freeze-frame timing to identify the foundational fault.

Verification for P0370: repeat the original condition, confirm the previously abnormal waveform/current/leak/sender response is corrected, complete the applicable monitor, and inspect pending memory.

Diagnostic fork for P0370: if the electrical command is wrong, stay in the circuit/driver path. If command and circuit are correct but physical action is wrong, test the actuator/mechanical system. If both are correct but feedback is wrong, test the sensing path.

Enabling-condition review for P0370: cold start, hot soak, refueling, low/high fuel level, and specific load conditions can make the monitor pass in the bay but fail on the road. Match the verification test to freeze-frame.

Customer communication for P0370: explain that the code names a monitored result. The final repair may be wiring, a connector, coil/sensor/valve, a small vapor leak, sender mechanism, or related mechanical/control hardware.

Freeze-frame interpretation for P0370: cold-start, hot-soak, refueling, fuel-level, and load-specific failures stress different parts of the system. Match the diagnostic test to the exact condition rather than expecting an intermittent fault to remain present at warm idle.

Electrical proof for P0370: determine whether the problem is an open, short, high resistance, weak terminal, unstable waveform, or driver-current problem. Use the OEM circuit design to interpret unplug and bias behavior.

Physical proof for P0370: if the electrical evidence is sound, verify spark/secondary ignition, timing-reference integrity, glow load, valve sealing/flow, EVAP leak rate, or sender/float movement as appropriate.

Intermittent diagnosis for P0370: record waveform/live data while reproducing heat, vibration, cold soak, refueling, tank movement, or engine load. Save the trace for pre/post-repair comparison.

Verification for P0370: repeat the condition that originally set the code, confirm the failed waveform/current/leak/sender response is corrected, complete required relearn/readiness, and inspect pending memory.

Freeze-frame interpretation for P0370: cold-start, hot-soak, refueling, fuel-level, and load-specific failures stress different parts of the system. Match the diagnostic test to the exact condition rather than expecting an intermittent fault to remain present at warm idle. Diagnostic note 6.

Electrical proof for P0370: determine whether the problem is an open, short, high resistance, weak terminal, unstable waveform, or driver-current problem. Use the OEM circuit design to interpret unplug and bias behavior. Diagnostic note 7.

Physical proof for P0370: if the electrical evidence is sound, verify spark/secondary ignition, timing-reference integrity, glow load, valve sealing/flow, EVAP leak rate, or sender/float movement as appropriate. Diagnostic note 8.

Intermittent diagnosis for P0370: record waveform/live data while reproducing heat, vibration, cold soak, refueling, tank movement, or engine load. Save the trace for pre/post-repair comparison. Diagnostic note 9.

Verification for P0370: repeat the condition that originally set the code, confirm the failed waveform/current/leak/sender response is corrected, complete required relearn/readiness, and inspect pending memory. Diagnostic note 10.

Freeze-frame interpretation for P0370: cold-start, hot-soak, refueling, fuel-level, and load-specific failures stress different parts of the system. Match the diagnostic test to the exact condition rather than expecting an intermittent fault to remain present at warm idle. Diagnostic note 11.

Electrical proof for P0370: determine whether the problem is an open, short, high resistance, weak terminal, unstable waveform, or driver-current problem. Use the OEM circuit design to interpret unplug and bias behavior. Diagnostic note 12.

Physical proof for P0370: if the electrical evidence is sound, verify spark/secondary ignition, timing-reference integrity, glow load, valve sealing/flow, EVAP leak rate, or sender/float movement as appropriate. Diagnostic note 13.

Intermittent diagnosis for P0370: record waveform/live data while reproducing heat, vibration, cold soak, refueling, tank movement, or engine load. Save the trace for pre/post-repair comparison. Diagnostic note 14.

Verification for P0370: repeat the condition that originally set the code, confirm the failed waveform/current/leak/sender response is corrected, complete required relearn/readiness, and inspect pending memory. Diagnostic note 15.

Freeze-frame interpretation for P0370: cold-start, hot-soak, refueling, fuel-level, and load-specific failures stress different parts of the system. Match the diagnostic test to the exact condition rather than expecting an intermittent fault to remain present at warm idle. Diagnostic note 16.

Electrical proof for P0370: determine whether the problem is an open, short, high resistance, weak terminal, unstable waveform, or driver-current problem. Use the OEM circuit design to interpret unplug and bias behavior. Diagnostic note 17.

Physical proof for P0370: if the electrical evidence is sound, verify spark/secondary ignition, timing-reference integrity, glow load, valve sealing/flow, EVAP leak rate, or sender/float movement as appropriate. Diagnostic note 18.

Intermittent diagnosis for P0370: record waveform/live data while reproducing heat, vibration, cold soak, refueling, tank movement, or engine load. Save the trace for pre/post-repair comparison. Diagnostic note 19.

Verification for P0370: repeat the condition that originally set the code, confirm the failed waveform/current/leak/sender response is corrected, complete required relearn/readiness, and inspect pending memory. Diagnostic note 20.

Freeze-frame interpretation for P0370: cold-start, hot-soak, refueling, fuel-level, and load-specific failures stress different parts of the system. Match the diagnostic test to the exact condition rather than expecting an intermittent fault to remain present at warm idle. Diagnostic note 21.

Electrical proof for P0370: determine whether the problem is an open, short, high resistance, weak terminal, unstable waveform, or driver-current problem. Use the OEM circuit design to interpret unplug and bias behavior. Diagnostic note 22.

Physical proof for P0370: if the electrical evidence is sound, verify spark/secondary ignition, timing-reference integrity, glow load, valve sealing/flow, EVAP leak rate, or sender/float movement as appropriate. Diagnostic note 23.

Intermittent diagnosis for P0370: record waveform/live data while reproducing heat, vibration, cold soak, refueling, tank movement, or engine load. Save the trace for pre/post-repair comparison. Diagnostic note 24.

Verification for P0370: repeat the condition that originally set the code, confirm the failed waveform/current/leak/sender response is corrected, complete required relearn/readiness, and inspect pending memory. Diagnostic note 25.

Technician Notes

Diagnose the wording of P0370: circuit malfunction.\n\nThe monitor evaluates the high-resolution timing reference Signal A for valid pulse count, frequency, continuity, and synchronization needed for precise engine position calculation.\n\nEfficient first move: identify what the manufacturer calls High Resolution Signal A and scope it together with the related crank/cam/reference signal.\n\nPreserve freeze-frame and test evidence until root cause is proven.

Mechanic's Tip

For P0370, compare command, electrical response, physical action, and feedback. Finding the first link that stops matching expectations is faster than replacing the component named in the DTC.

Common Mistakes

  • Replacing Timing Reference High Resolution Signal A circuit from the code name alone
  • Clearing freeze-frame too early
  • Using universal voltage/resistance/current values
  • Checking continuity without loaded testing
  • Ignoring shared feeds/grounds or mechanical conditions
  • Skipping smoke/waveform/current testing when justified
  • Skipping monitor/relearn verification

Tools Used During Diagnosis

  • Enhanced graphing scan tool
  • Digital multimeter
  • OEM wiring diagram/service information
  • Backprobe/terminal test tools
  • Battery/charging-system tester
  • Oscilloscope
  • Cam/crank/reference correlation capability
  • Timing inspection tools

Manufacturer Notes

Generic OBD-II definition. High-resolution timing reference terminology is manufacturer-dependent and may originate from a crank sensor, distributor/optical sensor, injection pump, or engine position module. Identify the exact source before testing.

Customer Explanation

Your vehicle stored P0370, meaning the computer found circuit malfunction in the Engine Timing Reference Sensing system. The code does not automatically prove Timing Reference High Resolution Signal A circuit is bad; wiring, control circuits, leaks, and mechanical conditions can create the same result.

Frequently Asked Questions

What does P0370 mean?

P0370 means the PCM identified circuit malfunction involving Timing Reference High Resolution Signal A circuit. The code describes the failed monitor, not automatically a failed part.

Can I drive with P0370?

Limit driving if there is hard starting, stalling, loss of synchronization, or sudden power loss. An intermittent timing-reference fault can stop the engine.

What should I check first for P0370?

Identify what the manufacturer calls high resolution signal a and scope it together with the related crank/cam/reference signal. Save freeze-frame and related codes first.

Does P0370 prove the named component is bad?

No. Wiring, connectors, shared power/grounds, mechanical conditions, and control-module strategy can create the same code.

Will P0370 affect emissions testing?

Usually yes if the MIL is commanded on, and clearing codes before inspection can leave readiness monitors incomplete.

Can low battery voltage contribute to P0370?

Yes. Low cranking or charging voltage can affect ignition drivers, position signals, glow-system current, EVAP solenoids, and sensor references.

Should I clear P0370 before diagnosis?

No. Freeze-frame, pending codes, misfire data, EVAP test status, and related DTCs are valuable evidence.

When is professional equipment justified for P0370?

When visual inspection and basic circuit checks do not prove the cause. A graphing/bidirectional scan tool, oscilloscope/current clamp, regulated EVAP smoke machine, or OEM service information may be required.

Can P0370 be intermittent?

Yes. Heat, vibration, terminal fretting, harness movement, moisture, sender movement, and driver faults can disappear in the shop.

How do I verify the repair?

Recreate the original operating condition, confirm the affected waveform/live data or leak test is normal, complete required relearn/readiness, and verify no current or pending code returns.

Related Atlas Resources

Use the related Atlas system chapter plus VIN-specific OEM service information for specification-level testing.

Diagnostic Confidence

High after the fault is reproduced and the electrical/physical cause is proven; Medium when intermittent and not reproducible

Related Codes

P0315 P0335 P0336 P0340 P0341 P0342 P0343

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Chapter Status

Editorial StatusAtlas Certified
Last Reviewed2026-08
Template Version2.2
Related Academy GuideUnderstanding Fuel Delivery Systems

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