Exhaust Gas Recirculation Sensor A Circuit Low
What does P0405 mean?
The P0405 code means the vehicle's onboard diagnostic system has detected: Exhaust Gas Recirculation Sensor A Circuit Low. This is a moderate severity code.
Common Symptoms
- Check Engine Light illuminated
- Rough idle
- Engine pinging or knocking
- Poor acceleration
- Failed emissions test
Probable Causes (Ranked by Likelihood)
- Faulty EGR position sensor Very High
- Short to ground in EGR sensor signal wire High
- Corroded EGR sensor connector Moderate
- ECM internal fault on EGR sensor input Low
Step-by-Step Diagnostic Procedure
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Check EGR position sensor voltage on a scan tool -- should read 0.5-1.0V with valve closed
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Inspect the EGR sensor connector for corrosion or water intrusion
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Disconnect the sensor and check if voltage rises -- if it stays low, check wiring for short to ground
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Verify 5V reference voltage is present at the sensor connector
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Replace the EGR valve assembly if the sensor is integrated and tests faulty
Frequently Asked Questions
Can I drive with code P0405?
You can drive short distances. The ECM cannot properly control EGR flow without accurate sensor feedback, which may cause rough running. Avoid heavy acceleration where engine knock could cause damage.
Can I replace just the EGR sensor?
On some vehicles the position sensor is a separate component that can be replaced individually. On many modern vehicles, the sensor is integrated into the EGR valve and the entire assembly must be replaced.
What voltage should the EGR sensor read?
With the EGR valve fully closed, the sensor typically reads 0.5-1.0V. Fully open, it should read 4.0-4.5V. P0405 sets when the ECM sees voltage below the expected minimum.