Comprehensive diagnostic guide for P0379 - Timing reference pulse B not detected

Overview

• What the code indicates: P0379 is a timing reference pulse fault on channel B. In open-source code definitions, it is described as "Ausência de pulsos do sincronismo de referencia - sinal B" (absence of timing reference pulses - signal B). In practice, this means the PCM/ECU did not detect the expected reference timing pulses on the B channel.
  • Source note: This interpretation comes from the OBD2 code definition listing. It aligns with the general OBD-II concept that timing-reference pulse inputs are monitored and a loss or corruption of those pulses sets a DTC in the timing-reference family.
• Where it fits in OBD-II: P0379 is a powertrain code within the timing-reference pulse family. Wikipedia's OBD-II references confirm that powertrain codes are used to monitor various engine-control parameters, and timing-reference pulse signals are among those monitored parameters.

Symptoms

• Transmission: MIL (Check Engine Light) illuminated or pending codes.
• Engine performance: Engine may fail to start, run poorly, stall, or run intermittently due to loss of a critical timing reference signal.
• Driveability: Possible rough idle, misfire symptoms, or surges in RPM as the ECU cannot synchronize ignition/fuel timing reliably.
• Scant data indicators: Live data may show loss of a stable timing reference signal on channel B or time-based pulses missing in the timing-reference waveform.
  Note: Symptoms are typical of a lost/invalid timing-reference input; exact symptoms can vary by vehicle and the function tied to the B reference channel.

Probable Causes

• Sensor/signal source issues (highest probability, ~40-60%)
  • Faulty timing reference sensor or channel B sensor (or its sensing element) producing no valid pulses.
  • Sensor wiring issues on the B channel (damaged conductors, open circuit, or degraded signal integrity).
• Wiring/connector problems (~20-30%)
  • Loose, corroded, damaged, or moisture-affected connectors to the timing reference sensor B, or harness damage.
  • Improper shielding or EMI affecting the B-channel signal.
• PCM/ECU related (~5-15%)
  • ECU input fault, misconfiguration, or firmware/calibration issue affecting B-channel interpretation.
  • Internal PCM fault causing failure to detect/interpret the B reference input.
• Mechanical or secondary timing issues (lower probability, ~5-15%)
  • Severe mechanical timing issues could disrupt reference pulses, though this is less common than a sensor/harness fault for a "reference pulse not detected" condition.

Diagnostic Approach

1) Confirm the fault and context

• Retrieve P0379 (and any related timing-reference codes such as P0370-P0378 if present) and freeze-frame data.
• Note any other DTCs that may point to related sensor/wiring or ECU issues (e.g., P0335 crank, P0340 cam, or power/ground faults).
• Verify the vehicle is current with the scan tool's readiness and that no other fault codes mask the symptom.
• Source reference: DTC collection and diagnostic approach are described in general terms by Wikipedia's OBD-II sections (Diagnostic Trouble Codes; Powertrain Codes).

2) Inspect power, ground, and harness integrity

• Check power supply and ground to the timing reference circuit (as specified by the vehicle's service information for the B-channel input). Look for corroded grounds, high resistance, or shared ground paths that could affect the signal.

• Inspect wiring harness for chafing, pin damage, or moisture intrusion, especially around connectors and near heat sources.

• Inspect connectors for bent pins, corrosion, or debris; reseat and apply dielectric with attention to locking tabs.

• Reference: The general concept of DTCs and their causes includes emphasis on sensor connectivity and wiring as part of troubleshooting.

3) Verify the B-channel signal physically

• If possible, back-probe the timing reference B circuit and observe the waveform with an oscilloscope or a suitable data-logging tool.
• Look for the presence/absence of pulses, correct amplitude, and clean edges. Compare with known-good waveform data for the specific vehicle and sensor type if available.
• Confirm sensor power (e.g., 5V reference) and ground are stable during operation.
• If waveform is missing or severely degraded, the fault is most likely in the sensor/signal circuit (sensor or wiring) rather than the PCM.

4) Cross-check related timing signals

• Check the related timing-reference channels (A and/or C if applicable) to determine if the issue is isolated to channel B or part of a broader timing-reference subsystem.
• Determine if other timing-related codes appear (e.g., P0370-P0378). A multi-channel issue can indicate a PCM problem or a common wiring harness problem.

5) Sensor replacement/repair options

• If the B-channel sensor is confirmed faulty or its waveform is not within specification, replace the sensor (or the entire B-channel sensor assembly as recommended by the vehicle's service information).
• Repair or replace damaged wiring or connectors in the B-channel circuit; ensure proper pin-to-pin alignment and secure locking.
• After repair, recheck to ensure the B-channel pulses are now present and within spec.
• Relearn/initialize procedures: Some systems may require a trunk of relearn or alignment procedures after sensor replacement per factory service information.

6) ECU/PCM considerations

• If sensor and wiring verify good and the PCM still fails to detect pulses, consider PCM software/firmware issues or internal fault.
• In some cases, a software update or reflash from the OEM may resolve detection logic errors.
• If available, perform data-logging of the timing-reference inputs to confirm a consistent failure pattern.

7) Final verification and tests

• Clear codes and perform a road test to verify the fault is resolved; monitor for reoccurrence of P0379 and observe any accompanying DTCs.
• Verify all related readiness monitors after repair.
• Confirm that the vehicle starts reliably and runs smoothly, with normal timing and ignition control.

Recommended test tools and procedures

• Basic scan tool to read P0379 and related codes; view live data for timing reference signals if supported.
• Oscilloscope or high-quality data logger to capture timing reference pulses (channel B) and verify waveform shape, frequency, amplitude, and stability.
• Multimeter/DVOM to check power and ground continuity on the B-channel circuit.
• Service information for the vehicle to identify exact pinout, expected voltages (reference voltage, sensor supply), and channel B behavior.
• General caution: When probing wiring, back-probe carefully to avoid damaging connectors and ensure safety if the engine is running.

Safety Considerations

• Work safely around the engine bay; avoid shorts or backfeeds when probing sensor circuits.

• Disconnect the battery when performing major wiring repairs where there is a risk of short circuits or accidental airbag/ECU faults; follow OEM procedures.

• Ensure the vehicle is secured and cannot shift during bench tests or while under test.

• If you have access to vehicle-specific service information, follow the OEM wiring diagrams and test procedures for the timing reference B circuit, as the exact sensor type and channel mapping vary by manufacturer.

Summary

• P0379 indicates absence of timing reference pulses on channel B, a sensor/wiring/ECU issue related to the timing-reference input. Begin with a thorough electrical check of the B-channel circuit, inspect wiring/connectors, verify sensor operation with live data and waveform testing, and consider ECU-related faults if the sensor and wiring test good. Use service data for exact pinouts and procedures, and re-test the vehicle after any repair to confirm the condition is resolved.

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

---