Emissions

P0405 — EGR Sensor A Circuit Low Voltage

Severity: medium Safe to drive

What P0405 means

The engine control module (ECM) is reading a voltage from the EGR valve position sensor (sensor A) that is lower than expected. The EGR valve normally routes some exhaust gas back into the intake to lower combustion temperatures and NOx emissions, and the sensor tells the ECM how far the valve is open. With a low signal, the ECM cannot control recirculation accurately and turns on the check engine light.

Symptoms

  • Check engine light on
  • Rough idle
  • Sluggish acceleration or hesitation
  • Slightly worse fuel economy
  • Failed emissions test

Possible causes

  1. Faulty EGR valve position sensor
  2. Damaged or corroded wiring or connectors in the sensor circuit
  3. Signal wire shorted to ground
  4. EGR valve sticking or not opening fully
  5. Carbon buildup in the valve and EGR passages
  6. ECM input circuit fault (rare)

How to diagnose

  1. Scan all modules and record the freeze frame data
  2. Check battery voltage and the 5 V reference supply at the sensor connector
  3. Inspect the EGR harness and connector for corrosion, chafing and bent pins
  4. Test the signal wire for a short to ground or an open circuit with a multimeter
  5. Compare commanded and actual EGR position in live data
  6. Remove the valve and inspect it and the passages for carbon, and check that it moves freely
  7. Where fitted, check vacuum lines and the control solenoid
  8. If the wiring is good, test the sensor against the manufacturer's specification

Common fixes

  • Repair the wiring or replace a damaged connector
  • Clean the EGR valve and passages
  • Replace the position sensor if serviced separately, or the whole EGR valve
  • Clear the code and confirm it does not return on a test drive

Questions and answers

Can I drive with a P0405 code?

Usually yes, for a short time. The engine may run roughly and emissions will be higher, so have it diagnosed soon.

Will cleaning the EGR valve fix P0405?

Only if carbon is making the valve stick. The code points to a low signal in the sensor circuit, so check the wiring and sensor supply first.

What most often causes P0405?

A failed EGR valve position sensor or damaged wiring and connectors are the most common causes. The valve itself or the ECM are less likely.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.