P0406
UniversalExhaust Gas Recirculation Sensor A Circuit High
Medium SeverityThis code indicates that the vehicle's engine control module (ECM) has detected a higher-than-expected voltage signal from the Exhaust Gas Recirculation (EGR) sensor. This can lead to the EGR system not functioning correctly, potentially causing issues with engine performance and increased emissions.
⚠️ Before You Begin (Safety First)
Always ensure the engine is off and cool before working on any engine components. Disconnect the battery's negative terminal to prevent electrical shorts and accidental starting. Use appropriate personal protective equipment, such as gloves and eye protection.
Common Symptoms
- Check Engine Light illuminated
- Rough idle
- Engine hesitation or stumble during acceleration
- Poor fuel economy
- Engine knocking or pinging
- Failed emissions test
Common Causes
- Faulty EGR sensor
- Damaged or corroded wiring in the EGR sensor circuit
- Poor electrical connection at the EGR sensor or PCM
- Blocked or clogged EGR passages (less common for high circuit, but can indirectly affect sensor readings)
- Faulty Powertrain Control Module (PCM) - rare
Frequently reported on: General/Universal
Diagnostic Steps
- Visually inspect the EGR sensor and its wiring harness for any signs of damage, corrosion, or loose connections. Ensure all connectors are securely seated.
- Using a multimeter, test the voltage at the EGR sensor connector with the ignition on (engine off) to verify proper reference voltage and ground. Compare readings to service manual specifications.
- Test the resistance of the EGR sensor itself (if applicable) and its signal wire for continuity. A 'high circuit' typically indicates an open circuit or a short to voltage.
- If the sensor or wiring is found to be faulty, replace the EGR sensor or repair the damaged wiring.
- Clear the P0406 code from the ECM and test drive the vehicle to confirm the repair.
👨🔧 When to Call a Professional
If you have replaced the EGR sensor and/or valve and performed basic wiring checks, but the code persists, it's time to consult a professional. Complex electrical diagnosis or potential powertrain control module (PCM) issues may require specialized tools and expertise.
Commonly Asked Questions
What does 'EGR Sensor A Circuit High' mean?
It means the vehicle's computer detected an unusually high voltage signal from the EGR sensor, suggesting an electrical problem within the sensor or its circuit.
Can I drive my car with a P0406 code?
While it's generally safe to drive for a short period, it's best to address it promptly. Prolonged driving with an active P0406 can lead to reduced engine performance, increased emissions, and potentially other engine problems.
What tools do I need to fix P0406?
You'll typically need a basic wrench set, a socket set, a multimeter for electrical testing, and potentially a diagnostic scan tool to clear the code.
How can I test the EGR sensor?
You can test the EGR sensor's voltage output and resistance using a multimeter. Consult your vehicle's service manual for specific voltage and resistance values for your make and model.
Is replacing the EGR sensor difficult for a DIYer?
The difficulty varies by vehicle. On some cars, the EGR sensor is easily accessible, making it a medium-level DIY task. On others, it may be harder to reach, requiring more advanced skills.