By iCarsoft Official Store Technical Team, Automotive Diagnostics Editors · Updated September 1, 2026 · OEM technical references checked
Quick Answer
The P0370 code means the controller detected an unacceptable result in the timing reference high-resolution signal A monitor. It does not prove the crankshaft sensor, injection pump or timing chain is automatically defective. Save the complete scan and operating conditions, identify the exact architecture, and test accessible mechanical and electrical paths before selecting a repair.
What Does the P0370 Code Mean?
P0370 is standardized as Timing Reference High Resolution Signal A. The description names a monitored result, not a guaranteed failed part. The reporting controller, suffix, current/pending/permanent status and related faults decide which test branch is relevant.
Depending on the engine, the reference may be produced by an optical encoder, injection-pump sensor, crank/cam sensing arrangement or another timing device. Signal A does not establish the connector, waveform, tooth count or physical source without service information.
Graph supported engine-speed, synchronization and timing-reference status while comparing scan data with the actual waveform when the OEM procedure permits it. A displayed value comes from the controller and may be substituted, filtered or unavailable. Confirm units and signal source before comparing it with a physical measurement.
GM Bulletin 00064H cross-references P0370 on specified diesel EFI applications with a diesel injection diagnostic worksheet. It shows one architecture, not proof that every P0370 vehicle has the same pump or sensor.
Separate P0370 from adjacent fault families
| Code | General description | Key distinction |
|---|---|---|
| P0370 | Timing reference high resolution signal A | Base monitor for signal A; read the OEM suffix and status. |
| P0371 | Signal A too many pulses | A pulse-count branch, not the same base result. |
| P0372 | Signal A too few pulses | Requires its own pulse-count and mechanical checks. |
| P0373/P0374 | Signal A intermittent/no pulses | Distinguishes dropout from complete absence in supported definitions. |
Record the complete P0370 description. Manufacturer suffixes, the module that stored it and companion faults can materially change the diagnostic path.
P0370 Symptoms and Likely Causes
P0370 symptoms depend on whether the fault is active and on the vehicle’s fallback strategy. Record what the driver and modules actually reported. A symptom list is not a parts list, and the absence of a symptom does not make the stored evidence irrelevant.
Some engines cannot establish timing when the high-resolution reference is absent.
A heat- or vibration-related dropout can stop combustion and later disappear.
The controller may use fallback information; the exact behavior is application-specific.
Crank, cam, pump or supply codes can establish the failure order.
Practical cause-checking order
- Accessible connection: connector, shield, terminal or harness damage near a hot or moving engine component.
- Circuit or shared path: unstable sensor or module supply and ground circuits.
- Supporting system: contamination, air gap, encoder or signal-source trouble identified by the OEM design.
- Named component: mechanical timing, drive or injection-pump condition that changes the expected relationship.
- Controller or software: controller input or calibration trouble only after waveform and mechanical checks pass.
Did P0370 appear after recent work? Recheck every disturbed connector, ground, bracket, fluid, adjustment, part number and setup step related to the high-resolution engine timing reference. Record battery disconnection, jump starting and software history. A post-repair code does not prove that the newly installed component is defective.
How Serious Is P0370, and Can You Drive?
Arrange diagnosis promptly. When the warning is steady, operation remains normal and the owner’s manual permits it, a short light-load trip to a repair facility may be reasonable. Avoid demanding use until the high-resolution engine timing reference is understood. P0370 does not provide a universally safe distance.
Tell the repairer exactly when the symptom occurred, including temperature, load, speed, start state and recent service. Do not deliberately reproduce a severe symptom on public roads merely to collect data. Stop sooner when another warning or a safety-related change appears.
Stop and arrange a tow if the engine stalls repeatedly, will not restart in a hazardous location, misfires severely, loses power unsafely, overheats, or develops new knocking, scraping, fuel leakage, or smoke
Rotating timing parts, belts, fans, high-pressure diesel fuel and hot exhaust are serious hazards. Do not loosen injection fittings or probe a running engine near moving components without the specified procedure.
How to Diagnose P0370 in the Right Order
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Save the complete fault record
Scan all accessible modules before clearing anything. Save P0370 wording, suffix, reporting module, status, freeze frame and companion codes. Record supply voltage and the relevant available data for the high-resolution engine timing reference. Note the failure order, recent repairs and whether a restart changes the behavior. Keep the original report for later comparison.
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Identify the VIN-specific monitor and architecture
Use the VIN, engine, transmission and equipment codes to obtain the current wiring diagram, connector views, monitor description and bulletins.
Depending on the engine, the reference may be produced by an optical encoder, injection-pump sensor, crank/cam sensing arrangement or another timing device. Signal A does not establish the connector, waveform, tooth count or physical source without service information. Confirm software identifiers and service-action eligibility directly; a bulletin for one application does not establish coverage for another.
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Inspect the accessible physical path
Follow the safety procedure, then inspect the connectors, locks, seals, terminals, clips and harness routing for the high-resolution engine timing reference. Look for heat, abrasion, fluid entry, corrosion, tension and unsuitable prior repairs. Check the supporting mechanical or fluid path named in the service information. Photograph evidence before correcting it.
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Prove circuits and physical conditions
Use a lab scope, high-impedance multimeter, appropriate breakout leads, and mechanical timing tools specified for the engine as the procedure requires. Prove feeds and grounds under the specified load, then test signal or control integrity at the correct states. Isolate components before resistance tests. Never bridge a controller pin to battery or ground, and do not substitute a continuity beep for a load or waveform test.
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Compare supported command and response
Graph supported engine-speed, synchronization and timing-reference status while comparing scan data with the actual waveform when the OEM procedure permits it. Compare scan evidence with the external measurement and companion faults. A command does not prove physical movement, pressure, current or torque. A missing PID or active test is a coverage limitation, not evidence that the vehicle component failed. Stop any test if operation becomes unsafe.
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Choose the supported repair and setup
Repair the path that failed its test, then correct the reason for damage and restore routing or adjustment. Confirm part application, required fluid or fasteners, programming authority and any relearn before replacement. Treat a controller as a late branch after its powers, grounds, inputs, outputs and current service information have passed.
Specifications are vehicle-specific. There is no universal voltage, resistance, current, pressure, waveform, timing, temperature, percentage or drive cycle for P0370. Test state, connector location and system design change what a valid value means. Use only specifications for the exact VIN and do not transfer the OEM example in this article to another application.
P0370 Repairs and Typical Costs
The correct P0370 repair follows the failed test. A terminal repair, restored supply, corrected fluid/mechanical condition, proven component replacement, software action or controller work are different outcomes. Replace neither the named part nor a large assembly from the generic code alone.
After installation, recheck connector seating, harness clearance and every setup step. If an OEM bulletin appears relevant, document the vehicle eligibility, installed calibration and prescribed action. The existence of the bulletin in the references does not promise warranty, free repair or a software cure for other vehicles.
| Possible path | Current US estimate |
|---|---|
| Initial diagnosis and evidence capture | VIN-specific quote |
| Confirmed connector, wiring, supply or ground repair | VIN-specific quote |
| Proven sensor, switch, actuator or mechanical repair | VIN-specific quote |
| Applicable software, setup or controller work | VIN-specific quote |
There is no single national P0370 repair price because these rows are alternative outcomes. Ask for an itemized estimate showing diagnostic time, parts, labor, fluids, programming access and verification. Location, taxes, related damage and warranty eligibility change the total. Do not add the rows together or authorize an assembly without the supporting failed test.
Using iCarsoft CR Eagle P for P0370
On a supported vehicle, iCarsoft CR Eagle P can retrieve accessible module faults, save available freeze frame, display ECU-provided live data and create a diagnostic report. For P0370, preserve the original evidence and compare related modules before clearing an erasable record.
Preserve the high-resolution engine timing reference evidence
iCarsoft CR Eagle P
Review supported codes and relevant live data together. Confirm the exact VIN, controller access, PIDs and any requested active test with iCarsoft before purchase; generic product capabilities do not guarantee a P0370-specific function.
Check current CR Eagle P price and availabilityCheck CR Eagle P compatibility by VINThe official product page describes full-system diagnosis and bidirectional functions, but the exact high-resolution engine timing reference data or output test depends on vehicle, ECU and software. Follow OEM prerequisites and stop for abnormal operation. A coding or J2534 feature does not itself supply the manufacturer file, subscription, authorization or procedure for an OEM bulletin.
Know the measurement boundary. The scanner reports information supplied by the vehicle. It does not directly prove terminal tension, circuit load capacity or the physical condition of the high-resolution engine timing reference. It also cannot replace a lab scope, high-impedance multimeter, appropriate breakout leads, and mechanical timing tools specified for the engine when the OEM procedure requires them. Interpret commanded and reported values alongside measured evidence.
Verify the P0370 Repair
After repair, verify connector locks, terminal seating, harness clearance, fluid or mechanical setup, and stable controller supply. Save post-repair findings, then clear only erasable records through the approved procedure after retaining the original evidence. Battery disconnection is not a substitute for correcting P0370.
Run the manufacturer’s applicable verification conditions in a safe workshop or route. Compare the original operating state with current data for the high-resolution engine timing reference, and check current and pending faults in related modules. One clean start or idle period does not prove that every conditional monitor has completed.
If P0370 returns, compare its suffix, status, failure order and operating conditions with the saved baseline before replacing another part. Revisit the failed branch and inspect anything disturbed. Keep mechanical repair, monitor completion, readiness and local inspection eligibility as separate outcomes.
A permanent P0370 can remain immediately after a successful repair. If the vehicle stores it as a permanent DTC, a scan tool or battery disconnect cannot erase it. Once current and pending faults are absent, the OBD system removes the permanent record only after the applicable monitor reruns and passes.
Related Timing Reference High Resolution Signal A Code Guides
P0370 Frequently Asked Questions
Does P0370 mean the high-resolution engine timing reference component is bad?
No. P0370 describes an unacceptable result in the timing reference high-resolution signal A monitor, not a confirmed part. Test accessible wiring, supplies, grounds and supporting mechanical conditions, then follow the exact monitor tree. Replace a component only when its branch fails or an applicable OEM action specifically supports it.
What should I check first for P0370?
Save every module’s codes and freeze frame before clearing. Confirm the full definition, suffix and VIN architecture. Then inspect recent work, connectors and shared supplies. Those low-cost facts determine whether the next test needs a lab scope, high-impedance multimeter, appropriate breakout leads, and mechanical timing tools specified for the engine or a manufacturer-specific functional procedure.
Can I drive with the P0370 code?
Only consider a short light-load trip when operation is normal and the owner’s manual permits it. Stop if the engine stalls repeatedly, will not restart in a hazardous location, misfires severely, loses power unsafely, overheats, or develops new knocking, scraping, fuel leakage, or smoke. The code number cannot establish a safe mileage allowance, and another warning can make the situation more urgent.
Why did P0370 return after a part was replaced?
The original circuit or supporting-system fault may remain, the part or setup may be wrong, or the first diagnosis may have confused a monitored result with a failed component. Compare the new failure conditions with the saved record and recheck every disturbed connection before buying another part.
How much does a P0370 repair cost?
A VIN-specific estimate is required because diagnosis may lead to wiring, a supporting mechanical repair, a verified component, software or a controller. Ask which failed test supports the quote and whether diagnosis, taxes, setup and post-repair verification are included.
Can CR Eagle P diagnose and clear P0370?
On a supported vehicle, CR Eagle P can organize available faults, freeze frame, live data and reports, and can clear erasable records after repair. Confirm exact ECU coverage. It cannot force-clear a permanent DTC or replace physical circuit and high-resolution engine timing reference measurements.
The iCarsoft Official Store Technical Team maintains the store's fault-code library. This guide organizes published manufacturer evidence and verified product information; it does not document a hands-on test of a particular vehicle or claim an individual engineer's review.
Technical and cost references
- Snap-on Diagnostic Trouble Codes (DTC) List. Current generic terminology cross-check for P0370; OEM suffix and service information take priority.
- GM Bulletin 00064H, Diesel EFI Diagnostic Worksheet, July 2014. Cross-references legacy DTC 17 to P0370 timing reference high resolution on specified GM diesel applications. Older OEM or legacy labels may append malfunction; the current standardized title used here does not.
- California Bureau of Automotive Repair — On-Board Diagnostic Test Reference. Permanent DTCs are removed by the vehicle after applicable verification, not by a scan-tool erase command.
Product information: Official iCarsoft CR Eagle P page.
Editorial note: This educational guide supports diagnostic planning and does not replace the current service manual, safety instructions, or professional diagnosis for your VIN. Source information was checked September 1, 2026. Apply only the procedures and specifications for the exact vehicle; product functions depend on vehicle, ECU, software, and access requirements.
