P0379

What Does Code P0379 Mean?

DTC P0379 indicates that the Engine Control Module (ECM), often referred to as the Powertrain Control Module (PCM), has detected an absence of pulses from the Timing Reference High Resolution Signal B. This specific code points to an issue with a secondary or high-resolution timing reference sensor, typically a crankshaft position (CKP) sensor or a camshaft position (CMP) sensor, that provides extremely precise rotational position data to the ECM/PCM. “High Resolution” signifies a sensor designed to deliver a high density of pulses per revolution, enabling the ECM/PCM to accurately determine engine speed, exact piston position (TDC, BDC), and precise angular velocity for critical functions such as ignition timing, fuel injection timing, variable valve timing (VVT) operation, and advanced misfire detection strategies. The “No Pulses” aspect means the ECM/PCM expects to see a signal waveform from this sensor during engine cranking or running conditions, but absolutely no signal or an inconsistent, uninterpretable signal is being received. When the ECM/PCM fails to detect the expected signal for a calibrated period or number of engine revolutions, it interprets this as a critical failure in timing reference acquisition and sets code P0379, illuminating the Malfunction Indicator Lamp (MIL).

Common Symptoms

• Engine cranking but no start.
• Extended crank times before engine starts.
• Engine stalls unexpectedly.
• Rough running or persistent misfires.
• Reduced engine performance and lack of power.
• Erratic idle speed or fluctuating RPMs.
• Illuminated Malfunction Indicator Lamp (MIL).

What Causes the Code P0379?

• Faulty Timing Reference Sensor: The primary cause is often a defective crankshaft position (CKP) sensor or camshaft position (CMP) sensor that corresponds to “Signal B.” This could be due to internal electrical failure, physical damage, or contamination.
• Damaged Wiring or Connectors: An open circuit, short to ground, or short to voltage in the sensor’s wiring harness can prevent the signal from reaching the ECM/PCM. Corroded, loose, or bent pins within the sensor or ECM/PCM connectors are also common culprits.
• Damaged Reluctor Wheel/Tone Ring: The reluctor wheel (also known as a tone ring or trigger wheel) on the crankshaft or camshaft provides the physical reference points for the sensor. Missing teeth, bent teeth, debris accumulation, or improper installation can disrupt the sensor’s ability to generate a consistent signal.
• Incorrect Sensor Installation or Air Gap: If the sensor is not correctly seated or if the air gap between the sensor and the reluctor wheel is outside manufacturer specifications, the signal strength or presence can be compromised.
• ECM/PCM Failure: While less common, an internal fault within the ECM/PCM’s input circuit for the timing reference signal can lead to P0379, even if the sensor and wiring are functional.

How to Diagnose and Troubleshoot

Diagnosing P0379 requires careful, systematic testing, ideally utilizing a professional scan tool and a digital multimeter (DMM), with an oscilloscope/lab scope being highly beneficial for signal verification.

1. Scan Tool Data and Freeze Frame: Connect an OBD-II scan tool and retrieve all stored DTCs and freeze frame data. Note any other related timing codes (e.g., P0335-P0339 for CKP, P0340-P0349 for CMP). Analyze live data streams for the CKP and CMP sensor readings while cranking or running the engine (if possible). A “no pulses” condition should be evident as 0 RPM or an erratic, non-existent signal from the relevant sensor.
2. Visual Inspection:
   • Locate the CKP and CMP sensors. Inspect the specific sensor associated with “Signal B” (consult service information for vehicle-specific identification).
   • Carefully inspect the sensor itself for physical damage, cracks, oil saturation, or metallic debris adhering to its tip.
   • Examine the entire wiring harness leading to the sensor and back to the ECM/PCM for signs of chafing, cuts, bare wires, or heat damage. Pay close attention to areas where the harness might rub against engine components.
   • Inspect the sensor and ECM/PCM connectors for corrosion, bent pins, pushed-back terminals, or loose connections.
   • If accessible, visually inspect the reluctor wheel (tone ring) for any missing teeth, physical damage, or excessive runout.
3. Circuit Testing (with DMM):
   • Power and Ground: Disconnect the sensor connector. With the ignition ON and engine OFF, use a DMM to check for the specified reference voltage (typically 5V or 12V) at the sensor’s power supply pin and a good chassis ground at the ground pin. A lack of voltage or poor ground indicates a wiring issue.
   • Signal Wire Continuity and Shorts: Turn the ignition OFF. Disconnect both the sensor connector and the ECM/PCM connector. Use the DMM to check for continuity between the sensor’s signal wire terminal and the corresponding terminal at the ECM/PCM. Look for an open circuit (OL reading) or resistance exceeding specifications. Also, check for shorts to ground and shorts to voltage on the signal wire.
4. Sensor Output Testing (Oscilloscope Recommended):
   • Inductive Sensors: For 2-wire inductive sensors, backprobe the sensor connector (or connect at the ECM/PCM) with an oscilloscope. Crank the engine and observe the AC voltage waveform. Expect a clean, consistent sine wave that increases in amplitude with engine speed. “No pulses” would show a flat line. A DMM set to AC voltage may show some fluctuating voltage during cranking, but an oscilloscope provides a definitive visual.
   • Hall Effect Sensors: For 3-wire Hall effect sensors, backprobe the signal wire with an oscilloscope. Crank the engine and observe the square wave signal. Expect a crisp, consistent on/off square wave corresponding to the rotational position. “No pulses” would indicate a constant high or low voltage.
5. Sensor Resistance Test (Inductive Sensors Only): Disconnect the inductive sensor and measure its internal resistance across its two terminals with a DMM. Compare the reading to manufacturer specifications. An open circuit (OL) or a reading significantly outside the specified range indicates a faulty sensor. Hall effect sensors cannot be tested this way.

Recommended Repairs and Solutions

Based on the diagnostic findings, the following repairs are typically recommended:

• Replace the Faulty Timing Reference Sensor: If testing confirms the CKP or CMP sensor identified as “Signal B” is defective (e.g., no output, incorrect resistance), replace it with a new, high-quality OEM or equivalent aftermarket part. Ensure the new sensor is properly seated and the air gap is correct according to service specifications.
• Repair or Replace Damaged Wiring/Connectors: Any identified open circuits, shorts, or corroded wiring in the sensor harness must be meticulously repaired or the entire sub-harness replaced. Use appropriate automotive-grade wire and connectors, ensuring waterproof connections. Clean any corroded terminals and ensure good pin tension.
• Repair or Replace Damaged Reluctor Wheel: If the reluctor wheel (tone ring) is found to be damaged, it must be repaired or replaced. This can be a labor-intensive job, often requiring significant engine disassembly (e.g., removing the crankshaft pulley, timing cover, or transmission for some CKP sensor reluctors).
• ECM/PCM Replacement (Last Resort): If all sensor, wiring, and reluctor components test within specifications, and a clear signal is reaching the ECM/PCM, but the module still reports “no pulses” or fails to operate correctly, then ECM/PCM replacement or reprogramming might be necessary. This should only be considered after exhaustive troubleshooting has ruled out all other possibilities.
• Post-Repair Verification: After any repair, clear the DTCs with a scan tool. Perform a comprehensive test drive under various engine loads and speeds to confirm the repair and ensure the P0379 code does not return. Monitor live data for consistent timing reference signals. Some vehicles may require a crankshaft position sensor relearn procedure after replacement; consult service information for specific requirements.