Exhaust Gas Recirculation Sensor A Circuit High
What does P0406 mean?
The P0406 code means the vehicle's onboard diagnostic system has detected: Exhaust Gas Recirculation Sensor A Circuit High. This is a moderate severity code.
Common Symptoms
- Check Engine Light illuminated
- Rough or unstable idle
- Engine stalling
- Reduced power and hesitation
- Failed emissions test
Probable Causes (Ranked by Likelihood)
- Faulty EGR position sensor reading high Very High
- Open ground wire to EGR sensor High
- Short to 5V reference in EGR sensor signal wire Moderate
- ECM internal pull-up fault on EGR circuit Low
Step-by-Step Diagnostic Procedure
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Check EGR position sensor voltage -- readings above 4.5V with valve closed indicate a fault
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Verify ground wire continuity from the sensor connector to the ECM
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Disconnect the sensor and measure voltage on the signal wire -- it should drop with sensor removed
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Check for chafed wiring where the signal wire may contact the 5V reference line
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Replace the EGR position sensor or EGR valve assembly if wiring checks out
Frequently Asked Questions
Can I drive with code P0406?
You can drive short distances. The ECM sees the EGR valve as fully open and may command it closed, or it may disable the EGR system entirely. This can cause rough idle and increased emissions.
What is the difference between P0405 and P0406?
P0405 indicates the EGR sensor voltage is below the expected range (too low), while P0406 indicates it is above the expected range (too high). Both point to the EGR position sensor or its circuit.
What causes the EGR sensor to read high?
A failed sensor, an open ground connection that lets the signal float high, or a signal wire shorted to the 5V reference are the most common causes of a high reading.