P0379
Timing Reference High Resolution Signal B No PulsesP0379 is a generic OBD-II powertrain diagnostic trouble code: Timing Reference High Resolution Signal B No Pulses. 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 P0379 means
P0379 is stored when the PCM receives absolutely no pulses from the high-resolution timing reference signal on channel "B". This is the most severe variant in the P037x channel "B" series, representing a complete loss of signal rather than degraded or intermittent performance. Channel "B" is the secondary high-resolution timing input, counterpart to channel "A" (P0374). Without any pulses, the PCM has no engine position data from this input and cannot accurately manage ignition timing, fuel injection timing, or misfire detection.
Whether P0379 causes a no-start condition depends on the engine architecture. On engines that rely solely on channel "B" for high-resolution position sensing — or that cannot operate without both channels — the engine will crank but not start. On engines where channel "A" provides sufficient fallback timing data, the engine may run in a degraded mode with reduced performance and possible misfires. In either case, the PCM will log the fault and typically illuminate the MIL.
The most common causes are a completely failed sensor, a severed or shorted signal wire, or a severely damaged reluctor wheel. Diagnosis should establish whether the sensor has power and ground, then verify signal output with an oscilloscope or scan tool live data at cranking speed.
Common causes
Most-frequently reported root causes when P0379 is logged.
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1
Complete failure of the channel "B" engine position sensor with no output signal.
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2
Severed, shorted-to-ground, or shorted-to-voltage signal wire eliminating the pulse signal at the PCM.
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3
Severely damaged reluctor wheel with missing or destroyed teeth across the entire sensing area.
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4
Total loss of sensor supply voltage or ground reference preventing sensor operation.
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5
PCM input circuit failure for the channel "B" timing line.
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6
Sensor connector fully disconnected or corroded to the point of open circuit on all pins.
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7
Timing belt or chain failure displacing the reluctor wheel out of sensor range on some applications.
Symptoms drivers notice
How to diagnose P0379
A typical diagnostic flow when this code is present.
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1
Connect a scan tool and record all codes; verify channel "B" sensor PID shows no signal or zero pulses during cranking.
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2
Confirm whether the engine starts — if it does not, note whether the channel "B" signal is the sole source of high-resolution timing.
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3
Inspect the sensor connector and wiring for complete disconnection, broken wires, melted insulation, or short circuits.
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4
Measure sensor supply voltage and ground at the connector; if power and ground are absent, trace the circuit fuse and feed wiring.
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5
Use an oscilloscope at the PCM harness connector to confirm whether any signal is present at cranking speed, ruling out a PCM input fault.
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6
Inspect the reluctor wheel for catastrophic damage or complete absence of teeth in the sensing window.
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7
Replace the sensor if power, ground, and wiring are confirmed good but no output signal is produced.
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8
If a new sensor does not resolve the code, inspect the PCM channel "B" input circuit for internal damage.
Related powertrain codes
Frequently asked questions
Will P0379 always cause a no-start?
Not always. On engines that use both channel A and channel B for timing, loss of channel B alone may allow the engine to run in a degraded mode using channel A as fallback. However, on engines that depend on channel B as the primary or sole high-resolution timing source, a complete loss of signal will prevent starting. Check the vehicle-specific wiring diagram to determine how critical channel B is for your application.
Is P0379 worse than P0377 or P0378?
Yes. P0377 (too few pulses) and P0378 (erratic pulses) describe a degraded signal that may still allow limited operation. P0379 means the signal is completely absent, representing the worst-case failure state in the channel B timing series. It has the highest probability of causing a no-start or severe misfire condition.
Can P0379 be caused by a timing belt failure?
Potentially, if the timing belt or chain drives the shaft carrying the channel B reluctor wheel (e.g., a camshaft tone ring). A jumped or broken timing belt can shift the reluctor wheel position relative to the sensor, resulting in no pulses being detected at the expected crank angle window.
How do I confirm the sensor is completely failed vs. a wiring issue?
Measure supply voltage and ground at the sensor connector with the ignition on. If supply and ground are correct but there is still no signal output during cranking, the sensor itself has failed. If either supply or ground is absent, the wiring or a blown fuse is the root cause, not the sensor.
Disabling P0379 in software
RaceTune can permanently disable P0379 — 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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