Emission controls · Powertrain · generic (SAE-defined)
P0405: Exhaust Gas Recirculation Sensor "A" Circuit Low
P0405 means the voltage signal from the exhaust gas recirculation (EGR) position or feedback sensor is lower than the normal range.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0405 sets
The powertrain control module (PCM) supplies a reference voltage to the EGR sensor and reads its signal. If the signal stays below the minimum expected value for a set time, such as from a short to ground or an open reference, the PCM sets P0405. Voltage limits vary by manufacturer.
Common causes of P0405
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Failed EGR position or differential pressure feedback sensor
- Signal wire shorted to ground
- Open or shorted 5-volt reference circuit
- Corroded or damaged sensor connector
- Disconnected or damaged sensor hoses on pressure-type sensors
P0405 symptoms
- Check engine light on
- Possible pinging or spark knock
- Often no drivability symptoms
How P0405 is diagnosed
- Check for other sensor reference voltage codes; a shared 5-volt reference fault can set several codes at once
- Inspect the sensor connector and harness for damage
- With key on, verify reference voltage and ground at the sensor connector
- Read the sensor signal in live data and compare to specification
- Check the signal wire for a short to ground
- On pressure-type sensors, inspect the hoses for cracks or blockage
Typical fixes for P0405
- Replace the EGR position or feedback sensor
- Repair shorted or open wiring
- Clean or replace the connector
- Replace cracked sensor hoses
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Manufacturer notes
Commonly associated with Ford DPFE sensors and GM integrated EGR valves. Definitions can vary by manufacturer; check factory service information.
Related codes & warning lights
P0405 FAQ
What does code P0405 mean?
P0405 means the voltage signal from the exhaust gas recirculation (EGR) position or feedback sensor is lower than the normal range. The standard definition is "Exhaust Gas Recirculation Sensor "A" Circuit Low."
Can I drive with a P0405 code?
Generally yes. The engine often runs normally, though the computer may disable EGR, which can lead to pinging under load. Have the sensor circuit checked soon.
What is the difference between P0405 and P0406?
P0405 indicates the sensor signal is reading too low, while P0406 means it is reading too high. Both point to the sensor or its wiring rather than EGR flow itself.
Do I need to replace the whole EGR valve for P0405?
On some engines the position sensor is built into the valve, so the assembly is replaced. On others the sensor is separate, such as a differential pressure sensor mounted nearby.
Keep researching
More emission controls codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.