P0373 - Timing Reference High Resolution Signal A Intermittent/Erratic Pulses
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P0373 diagnostic trouble code (DTC) indicates that the Engine Control Unit (ECU) has detected erratic or intermittent pulses from the high-resolution timing reference signal 'A'. This signal is typically generated by an optical or Hall-effect sensor providing a high frequency of pulses per engine revolution to allow the ECU to precisely control fuel injection timing and ignition. When the ECU detects 'noise', missing pulses, or extra pulses that do not correlate with the base timing signal, P0373 is stored. This causes significant issues with engine synchronization.
Possible Causes
Faulty high-resolution sensor (optical unit or Hall-effect sensor)
Electrical interference (EMI) from ignition wires or alternator
Damaged reluctor wheel or accumulation of debris/metal shavings
Wiring issues (intermittent open/short or corroded connectors)
Symptoms
Recommended Solution
- Visual Inspection: Check wiring and connectors leading to the sensor for chafing, oil contamination, or corrosion.
- Electrical Test: Use a multimeter to verify reference voltage (typically 5V or 12V) and ground at the sensor connector.
- Advanced Diagnosis (Oscilloscope): Scope the signal output while the engine is running. Look for a clean, consistent square wave pattern. Inspect for 'noise' or dropouts in the signal. Check for excessive AC ripple from the alternator which can cause EMI.
- Component Replacement: If the signal is erratic despite good power and ground, replace the sensor. Ensure the reluctor wheel is clean and free of metal debris.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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