Exhaust Gas Recirculation Sensor A Circuit Low
The Powertrain Control Module (PCM) detected that the voltage signal from the Exhaust Gas Recirculation (EGR) position sensor 'A' is lower than the manufacturer's specified minimum threshold. This typically indicates a short to ground or a faulty sensor, preventing the PCM from accurately monitoring the EGR valve's position.
While not immediately dangerous, driving with this code can lead to increased emissions, reduced fuel economy, and potential engine pinging (detonation). It should be diagnosed and repaired soon to prevent long-term engine or catalytic converter issues.
Common symptoms
- Illuminated Check Engine Light
- Engine pinging or knocking on acceleration
- Rough idle or stalling
- Decreased fuel efficiency
- Failed emissions test
Likely causes
- Faulty EGR valve position sensor
- Short to ground in the EGR sensor signal circuit
- Damaged or corroded EGR sensor connector
- Carbon buildup preventing the EGR valve from moving
- Faulty Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Scan for codes and monitor EGR position sensor live data.
Look for: Check if the EGR position sensor voltage reads near 0 volts or stays fixed below the minimum threshold (usually around 0.5V) when the valve is commanded open.
Visually inspect the EGR sensor wiring harness and connector.
Look for: Look for chafed wires, melted insulation, or corroded pins that could cause a short to ground or an open circuit.
Test the 5-volt reference and ground circuits at the EGR sensor connector.
Look for: With the key on and engine off, verify there is a steady 5V reference and a good ground. Missing voltage indicates a wiring or PCM issue.
Test the EGR sensor signal wire for a short to ground.
Look for: Disconnect the sensor and PCM, then measure resistance between the signal wire and ground. Continuity indicates a short to ground in the wiring harness.
Remove and inspect the EGR valve for carbon buildup.
Look for: Look for heavy carbon deposits that might be physically jamming the valve closed, preventing the pintle from moving and altering the sensor reading.
This page explains the generic P0405 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
Gear guide: Best OBD2 ScannersRead this code yourself next time — from $20 Bluetooth dongles to bidirectional scan tools.Rather have a pro handle it? Find a vetted local mechanic.