P0370 Code: High-Resolution Timing Signal A
P0370: Identify the Timing Reference Source
Keep the full starting, stalling and timing-code record before replacing any sensor.
DIAGNOSTIC FOCUS
- FAULT TYPE
- High-resolution timing-reference A integrity
- FIRST CHECKS
- Engine architecture, signal path and companion timing
High resolution does not mean high voltage or excessively advanced timing.
P0370 means Timing Reference High Resolution Signal A. High resolution does not mean high voltage or excessively advanced timing. Identify the vehicle-specific monitored system and test the relevant branch before replacing parts.
Preserve the original scan and freeze frame. Identify the actual circuit or monitored system before selecting a repair; the named component is not automatically defective.
What Does the P0370 Code Mean?
Timing Reference High Resolution Signal A identifies a monitored concern, not a guaranteed failed component. Preserve the reporting module, complete suffix and current/history status before selecting the OEM procedure.
The manufacturer examples below explain the relevant system and diagnostic distinctions. Their applicability and test limits remain vehicle-specific.
No universal voltage, resistance, current, pressure, waveform or drive cycle follows from this code. The exact VIN procedure controls the measurements.
P0370 concerns the designated high-resolution timing-reference A signal. The cited GM 6.5L electronic diesel example uses an injection-system timing-reference diagnostic path; identify the actual source on other engines before selecting a sensor or test.
High resolution does not mean high voltage or excessively advanced timing.
The code does not establish these conclusions: Timing chain has stretched; Crank sensor must be replaced; Injection pump must be replaced; The signal has too many, too few or zero pulses solely from P0370. These are questions to resolve with evidence, not reasons to skip the named circuit.
P0370 Symptoms, Severity, and Driving Safety
Hard starting, stalling, uneven running or limited performance are possible if the timing reference is disturbed. Code identity does not establish a mechanical timing error.
Record when this actually occurs and whether the warning appears at the same time.
This possibility is not a diagnosis; distinguish it from companion faults.
Preserve the exact message and operating state before clearing anything.
Compare normal and failing conditions without deliberately repeating a hazardous event.
Check companion records and their timing before assuming a shared cause.
Hard starting, stalling, uneven running or limited performance are possible if the timing reference is disturbed. Code identity does not establish a mechanical timing error. Follow the owner's manual and assess the actual symptoms. No universal safe mileage follows from this code. Arrange professional transport when safe response or reliable engagement cannot be established.
P0370 Causes and the Evidence That Separates Them
These are six possibilities to distinguish, not a frequency ranking. Use the recorded conditions to select a test that separates one branch from another.
Signal connector fault
Poor contact can interrupt the high-resolution reference.
How to prove it: Inspect the actual source connector and compare signal continuity through the event.
Check firstSupply or ground disturbance
A valid sensor or signal generator cannot operate correctly without its required support circuits.
How to prove it: Check its own power and ground under the prescribed operating conditions.
Check firstCorrupted signal wiring
Noise, damage or poor shielding may corrupt pulses while a scan tool still reports average RPM.
How to prove it: Use the correct waveform and routing checks rather than relying only on displayed RPM.
Verify directlySignal generator problem
The physical reference generator may fail to provide the required information.
How to prove it: Identify the source first; it is not universally a crankshaft or camshaft sensor.
Verify directlyOptical or mechanical target concern
Some injection-system architectures use an internal sensing or target path.
How to prove it: Investigate that branch only when the engine actually uses it and external circuit tests support it.
Verify directlyReceiver interpretation fault
The controller may fail to process otherwise valid reference information.
How to prove it: Prove the input, supplies and applicable software before controller diagnosis.
Final branchConfirm each finding with a controlled retest before replacing parts.
Using MA900 During P0370 Diagnosis
The iCARZONE MA900 OBD2 Scanner and Battery Tester supports accessible generic engine codes, freeze frame, live data and readiness, plus 12V/24V battery tests.
MA900 does not guarantee full-system access. Dedicated modules, enhanced records, active tests, coding and relearns require separately confirmed equipment coverage.
Battery tests support a relevant supply-voltage branch. They do not prove sensor waveforms, actuator response, hydraulic pressure or controller failure. Use the independent OEM-required equipment.
iCARZONE MA900 2-in-1 OBD2 Diagnostic Scanner & 12V/24V Battery Tester
Save accessible engine evidence for P0370; use an OEM-capable tool when the relevant module or function is not supported.
Checked September 7, 2026: $69.99 USD, compared with $99.99 on the official page. Stock was not confirmed; recheck price, availability and required vehicle/function coverage.
How to Diagnose P0370 in 6 Steps
Use these six steps with the exact manufacturer procedure. Confirm equipment coverage and safe test conditions before using any active command; a visible menu item does not establish applicability.
P0370 Quick Diagnostic Path
-
1
Save timing and starting evidence
- Save starting/stalling context, complete timing/injection codes and freeze frame.
- Retain original codes and conditions before disconnections or erasure.
-
2
Identify the signal A generator
- Identify the physical generator of high-resolution signal A from exact engine information rather than assuming a generic cam/crank sensor.
- Match the VIN, connector view and required test state.
-
3
Inspect its connector and supplies
- Inspect its connector, power/ground and wiring path, including contamination or prior-service disturbance.
- Document findings, then make one controlled correction at a time.
-
4
Compare timing-reference waveforms
- Compare high-resolution timing-reference evidence with the companion timing reference using the OEM waveform/pulse procedure; scan RPM alone may hide missing or corrupt pulses.
- Unavailable scan data is not a zero reading.
-
5
Test the applicable sensing target
- Investigate signal target, optical/mechanical sensing path or internal pump components only on architectures that actually use them and after circuit checks.
- Use approved isolation and equipment; never power an unknown circuit.
-
6
Verify stable starting and timing
- Verify repeatable start/run and stable timing evidence after repair; follow GM's warning against replacing the PCM or pump before service-manual diagnosis.
- Confirm the relevant monitor ran after the proven repair.
How to Fix P0370 and Verify the Repair
Signal connector fault repair
Inspect the actual source connector and compare signal continuity through the event. Repair only the proven fault and retain the after-repair test result.
Supply or ground disturbance repair
Check its own power and ground under the prescribed operating conditions. Repair only the proven fault and retain the after-repair test result.
Corrupted signal wiring repair
Use the correct waveform and routing checks rather than relying only on displayed RPM. Repair only the proven fault and retain the after-repair test result.
Signal generator problem repair
Identify the source first; it is not universally a crankshaft or camshaft sensor. Repair only the proven fault and retain the after-repair test result.
Diagnostic time
VIN-specific quoteRequest safe fault reproduction and the correct tests, not merely a generic code read.
Wiring or supporting-system work
VIN-specific quoteItemize connector, harness, ground or prerequisite work with the measurement supporting it.
Proven component or assembly
VIN-specific quoteConfirm the VIN-specific part, labor, taxes and warranty in a current local quote.
Setup and verification
VIN-specific quoteInclude only required learning, calibration and verification. These are alternative paths, not four mandatory repairs.
Get a current VIN-specific estimate showing the failed test, proposed repair and verification. A code alone does not justify an assembly replacement.
Verify repeatable start/run and stable timing evidence after repair; follow GM's warning against replacing the PCM or pump before service-manual diagnosis. If the event returns, investigate the unresolved branch rather than repeating a clear-and-drive cycle.
P0370 OEM Differences and DIY Limits
GM Bulletin 00064H includes a diagnostic worksheet for listed 6.5L electronic diesel applications. It cross-references the older code 17 to P0370 and separates pump, crankshaft and timing-control concerns. It warns against pump or PCM replacement before service-information diagnosis.
High resolution does not mean high voltage or excessively advanced timing.
Match the VIN, equipment, code suffix and failure conditions before applying a bulletin. A similar symptom is insufficient.
MA900 supports accessible generic engine information and battery testing. Dedicated modules, waveforms, active tests and programming require separately confirmed equipment.
Confirm current VIN, equipment, calibration and suffix applicability. A historical bulletin is not a warranty promise or a procedure for another application.
- Save codes and freeze frame before erasing.
- Record VIN, symptoms and recent repair history.
- Inspect only safely accessible, de-energized areas.
- Request the documented failed test and estimate.
- Never bypass safety interlocks or bridge unknown circuits.
- Do not guess pinouts or transfer another engine’s limits.
- Do not reproduce unsafe symptoms on the road.
- Leave invasive testing and programming to equipped professionals.
Frequently Asked Questions About P0370
What does P0370 mean?
Does high resolution mean high voltage?
What should I check first for P0370?
Can I keep driving with P0370?
Why can P0370 return after a part was replaced?
Can MA900 complete the entire P0370 diagnosis?
Will clearing P0370 prove that it is fixed?
What should a P0370 repair estimate include?
Sources and Technical Review Notes
- GM Bulletin 00064H: Electronic Diesel-Fuel Injection Pump Failure — Repair/Replace, including Diesel EFI Diagnostic Worksheet — Application-specific manufacturer evidence discussed above. Verify current VIN applicability before using its tests or remedies.
- Snap-on Diagnostic Trouble Codes (DTC) List — Current diagnostic-equipment manufacturer terminology cross-check; vehicle-specific testing still requires OEM service information.
- California Bureau of Automotive Repair — On-Board Diagnostic Test Reference — Explains emissions readiness and permanent-DTC verification; applicable emissions rules and vehicle behavior must be considered.
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