P0370
Timing Reference High Resolution Signal A MalfunctionP0370 is a generic OBD-II powertrain diagnostic trouble code: Timing Reference High Resolution Signal A Malfunction. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0370 means
P0370 — "Timing Reference High Resolution Signal \"A\" Malfunction" — is set when the PCM detects a general, non-specific fault in the engine's high-resolution timing reference signal \"A\". Unlike the standard crankshaft position sensor (which generates a fixed number of pulses per revolution, often 58 or 60), the high-resolution timing reference system produces a much higher pulse density — dozens to hundreds of pulses per revolution — to give the PCM extremely precise crankshaft angle data. This is used for individual cylinder timing trim, knock window positioning, and on older optical-distributor systems, for fuel injection phasing.
The high-resolution signal \"A\" can originate from several sources depending on the platform: an optical sensor inside a distributor housing (Ford EEC-IV/V, older Honda DOHC, GM 6.5L diesel Stanadyne pump), a dedicated high-tooth-count reluctor ring on the crank snout, or a secondary Hall sensor reading a fine-pitch encoder wheel. The code fires when the PCM cannot obtain a valid signal at all, receives a signal that is completely absent when the engine is turning, or detects that the signal is arriving at times that are inconsistent with engine position — completely wrong rather than just offset.
The practical effect is usually significant: without the high-resolution reference, the PCM may be unable to calculate precise ignition advance, may disable individual cylinder timing corrections, or on distributor-based systems may lose injection synchronisation entirely. Hard starting, severe misfires, and very poor performance are common, and on some platforms the engine will not run at all without a valid high-resolution signal.
Common causes
Most-frequently reported root causes when P0370 is logged.
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1
Failed optical sensor (distributor CPS on Ford EEC-IV/V, older Honda, or GM 6.5L Stanadyne pump) — contamination or LED/phototransistor failure eliminates the signal entirely.
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2
Damaged high-resolution reluctor wheel or encoder disc — cracks, missing segments, or physical damage causing erratic or absent signal output.
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3
Open circuit or short to ground on the high-resolution signal wire between sensor and PCM.
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4
Corroded or loose connector at the sensor or inline harness connector, intermittently or permanently breaking the signal path.
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5
Oil or coolant contamination inside the optical sensor housing blocking the light beam.
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6
Faulty crankshaft or camshaft position sensor on platforms where the high-resolution signal is derived from a standard CKP/CMP with a high-tooth-count wheel.
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7
PCM input circuit fault rendering it unable to process the high-frequency pulse train (rare).
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8
Mechanical distributor fault (shaft wear, wobble) causing signal timing to be completely uncorrelated with true engine position.
Symptoms drivers notice
How to diagnose P0370
A typical diagnostic flow when this code is present.
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1
Connect an OBD-II scan tool and record all codes; note any crankshaft position (P0335–P0338), camshaft position, or misfire codes stored alongside P0370.
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2
Identify which physical sensor produces the high-resolution signal \"A\" on this specific vehicle — consult the OEM wiring diagram, as the sensor type (optical vs. magnetic) and location vary greatly between platforms.
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3
On optical-distributor systems: remove the distributor cap and inspect the optical disc and sensor for oil contamination, cracks in the disc, and LED or phototransistor condition; clean if contaminated and retest.
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4
Measure sensor supply voltage and ground at the connector; confirm the correct reference voltage is present according to the OEM specification.
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5
Monitor the high-resolution signal PID on a scan tool while cranking; a completely absent signal during cranking confirms sensor or circuit failure.
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6
Perform wiring continuity and short tests on the signal wire between the sensor connector and PCM pin.
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7
Inspect the reluctor ring or encoder disc for physical damage, ensuring all teeth or windows are intact and the mounting is secure without wobble.
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8
If sensor and wiring test clean, test the PCM input circuit by substituting a known-good PCM or performing a controlled signal injection test.
Related powertrain codes
Frequently asked questions
Which vehicles most commonly trigger P0370?
Ford vehicles equipped with EEC-IV and EEC-V engine management systems with optical distributor sensors are classic examples, as are older Honda DOHC engines and GM 6.5L diesel trucks using the Stanadyne optical injection pump. Modern engines with high-tooth-count CKP reluctor wheels also set this code if that wheel or its sensor fails, though modern vehicles are more likely to set P0335.
What is the difference between P0370 and P0335?
P0335 relates to the standard crankshaft position sensor circuit. P0370 is specific to the high-resolution timing reference system, which is a separate, higher-density signal used for precise angle-degree calculations rather than basic RPM sensing. On platforms with only one CKP sensor, the codes may overlap in symptom, but on systems with a separate high-resolution encoder the two codes are distinct.
Can dirty oil cause P0370?
On optical sensor systems, yes. Dirty or aerated oil that enters the optical housing can coat the lens and phototransistor, blocking the light beam and eliminating the signal. Regular oil changes and ensuring the distributor or sensor housing seals are intact will prevent this failure mode.
Is P0370 safe to drive with?
Not reliably. On platforms that depend heavily on the high-resolution signal for injection phasing or individual cylinder timing, the engine may run very poorly or refuse to run at all. Even where the engine remains running, the degraded timing precision can cause damaging knock events. The code should be addressed before continued use.
Disabling P0370 in software
RaceTune can permanently disable P0370 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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