P0405: EGR Sensor A Circuit Low Voltage
The P0405 code indicates that the Engine Control Module (ECM) has detected a low voltage signal from the Exhaust Gas Recirculation (EGR) position sensor 'A'. This sensor monitors the position of the EGR valve to ensure proper exhaust gas recirculation. A low voltage reading typically means the sensor is reading a fully closed position or there is an electrical fault. Common causes include a faulty EGR position sensor, a stuck closed EGR valve, wiring issues (shorted or open circuit), or a poor electrical connection. This can lead to increased NOx emissions, rough idle, and reduced fuel economy.
01. Most Common Causes
- Faulty EGR position sensor
- Stuck closed EGR valve
- Shorted or open wiring in sensor circuit
- Poor electrical connection at sensor or ECM
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Rough idle or engine hesitation
- Increased emissions (failed smog test)
- Reduced fuel economy
03. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm code P0405 and check for additional codes.
Step 2: Visually inspect the EGR valve and sensor wiring for damage, corrosion, or loose connections.
Step 3: Test the EGR position sensor voltage with a multimeter; compare to manufacturer specifications.
Step 4: Check the EGR valve operation by applying vacuum or using a scan tool to command it open/closed.
Step 5: If sensor voltage is low and wiring is good, replace the EGR position sensor or EGR valve assembly.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
You can drive short distances, but it may cause rough idle, reduced fuel economy, and increased emissions. Prolonged driving could damage the catalytic converter or cause other issues.
How much does it cost to fix?▼
Typically $50-$150 for parts (EGR sensor or valve) plus labor if done by a shop. DIY replacement can save on labor costs.