Exhaust Gas Recirculation Sensor A Circuit High
The EGR (Exhaust Gas Recirculation) Sensor A circuit is reading a voltage level that is higher than the expected range, indicating the sensor signal is shorted to battery voltage or the 5V reference circuit. This causes the engine computer to detect an electrical fault in the EGR sensor circuit, triggering the check engine light.
What You Might Notice
- Check engine light (MIL) illumination
- Increased combustion temperatures and NOx emissions
- Engine surging or hesitation while driving
- Intermittent stalling or rough idle
- Possible decrease in fuel economy
Most Common Causes
- 1
EGR sensor signal circuit shorted to battery voltage
The wiring between the EGR sensor and engine control module has shorted to the positive battery voltage, causing the circuit voltage to exceed normal operating parameters.
- 2
EGR sensor signal circuit shorted to 5V reference
The sensor signal line is contacting the 5-volt reference circuit, causing an abnormally high voltage reading that the PCM interprets as a circuit fault.
- 3
Defective EGR sensor
The EGR sensor itself has failed internally and is producing an out-of-range high voltage signal, or the sensor connector pins are corroded causing poor contact.
- 4
Damaged wiring harness or loose connections
Corroded, damaged, or improperly seated connectors in the EGR sensor circuit can cause intermittent high voltage readings and circuit faults.
How to Diagnose It
- 1
Check EGR sensor signal circuit shorted to battery voltage — The wiring between the EGR sensor and engine control module has shorted to the positive battery voltage, causing the circuit voltage to exceed normal operating parameters.
- 2
Check EGR sensor signal circuit shorted to 5V reference — The sensor signal line is contacting the 5-volt reference circuit, causing an abnormally high voltage reading that the PCM interprets as a circuit fault.
- 3
Check Defective EGR sensor — The EGR sensor itself has failed internally and is producing an out-of-range high voltage signal, or the sensor connector pins are corroded causing poor contact.
- 4
Check Damaged wiring harness or loose connections — Corroded, damaged, or improperly seated connectors in the EGR sensor circuit can cause intermittent high voltage readings and circuit faults.
How to Fix It
- 1
Inspect and repair EGR sensor wiring
Visually inspect the EGR sensor wiring harness for damage, corrosion, or pinched wires. Check connector pins for corrosion and clean or replace as needed. Ensure all connections are fully seated and secure.
- 2
Test EGR sensor voltage with multimeter
Using a digital multimeter, measure the voltage at the EGR sensor signal line while the engine is running. Compare to manufacturer specifications; if reading is excessively high, proceed to sensor replacement.
- 3
Replace EGR sensor
If voltage testing confirms the sensor is faulty, remove the defective EGR sensor and install a new one. Ensure the connector is properly sealed to prevent moisture intrusion.
- 4
Clear code and perform verification drive
After repairs, use a diagnostic scanner to clear the P0406 code from the engine control module. Perform a test drive under various driving conditions to confirm the code does not return.
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