P0405 code is a generic diagnostic trouble code (DTC) related to the powertrain, applicable to vehicles equipped with OBD-II. Although generic, repair steps vary by make and model. This code indicates a malfunction in the exhaust gas recirculation (EGR) system, specifically an EGR valve feedback circuit with abnormally low voltage.
2. EGR System Operation
Role of the EGR
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Reduces NOx (nitrogen oxides) emissions by lowering combustion temperatures.
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Injects inert exhaust gases into the cylinders, limiting the amount of available oxygen.
EGR Activation
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Not activated: During cold start or at idle.
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Activated: During partial acceleration, deceleration, or depending on engine load and temperature.
Types of EGR Systems
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Electrical systems:
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Controlled directly by the PCM (powertrain control module).
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Components: 1-2 grounds, 12V power supply, 5V reference circuit, feedback circuit.
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Vacuum systems:
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Use a vacuum solenoid controlled by the PCM.
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Include an electrical connector for feedback.
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3. Symptoms of Code P0405
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Illumination of the malfunction indicator lamp (MIL).
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Unstable idle or loss of power.
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Increased pollutant emissions.
4. Possible Causes
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Electrical problems:
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Short to ground or voltage in EGR circuits.
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Damaged wires, loose terminals.
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Mechanical failures:
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EGR valve stuck (carbon, debris).
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Faulty PCM (often accompanied by other codes).
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5. Diagnostic Procedures
Step 1: EGR Valve Test
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Use a scan tool to command the valve.
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If feedback is normal → Intermittent problem (e.g., freezing or dirt).
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If no response → Check wiring and power supply.
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Step 2: Electrical Circuit Check
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5V reference circuit:
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Measure voltage with a voltmeter (KOEO: Key On, Engine Off).
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No 5V: Look for short circuits or open circuits.
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EGR signal circuit:
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Connect the 5V to the signal circuit.
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If the scan tool does not indicate 100%, check for short circuits to ground.
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Step 3: Replacement or Repair
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If wiring is intact → Replace the EGR valve.
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If PCM is suspected → Check for other codes.
6. Related EGR Codes
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P0400: Insufficient EGR flow.
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P0401/P0402: EGR flow too low/high.
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P0403/P0404: Control circuit problem.
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P0406-P0409: Circuit or position anomalies.
7. Conclusion
P0405 code indicates an EGR valve feedback problem, often related to electrical faults or clogging. A methodical check of the circuit and valve allows quick identification of the malfunction source. If in doubt, consulting a professional is recommended.