Category: Powertrain → EGR System
What it means (plain English)
The ECM/PCM sees a voltage signal lower than expected from the EGR position sensor (often <0.35V). It thinks the EGR valve is closed or the circuit is shorted to ground. (obd-codes.com)
Symptoms you’ll notice
- MIL on (repairpal.com)
- Rough idle, hesitation, or stalling
- Increased NOx emissions (failed emissions test)
- Poor fuel economy
- In diesels: derate mode, poor throttle response
Priority level
Medium–High. Incorrect sensor signals can mislead the ECM, affecting drivability and emissions.
Common causes
- Failed EGR position sensor (shorted internally) (yourmechanic.com)
- Short to ground in signal wire
- Broken wiring / corroded connectors
- Faulty EGR valve (integrated sensors on many modern designs)
- Rare: ECM input fault
How pros diagnose it
- Scan tool: confirm voltage at EGR position PID (should sweep ~0.5–4.5V).
- Back-probe sensor: check reference 5V, ground, and signal return.
- Wiggle harness: look for voltage dropouts.
- Bench test valve movement: confirm sensor voltage tracks smoothly.
- Check wiring continuity/shorts to ground.
Likely fixes
- Replace EGR position sensor or valve
- Repair/replace damaged wiring/connectors
- Clear codes and retest under varying loads
Related / companion codes
- P0404 (Range/Performance)
- P0406 (Sensor Circuit High)
- P0401/P0402 (Flow insufficient/excessive)
Tech notes
Ford/Chrysler products often set P0405 when the feedback circuit drops out due to wiring corrosion at the connector.