enbgde
P0405 Generic (SAE)

Exhaust Gas Recirculation Sensor A Circuit Low

Updated 2026-10-02 · Auxiliary emission controls

Severity
Medium
Typical repair cost
60 – 550 EUR
System
Powertrain

What it means

Electric EGR valves carry a position sensor, usually a potentiometer or Hall sensor fed with 5 V, so the ECM can confirm the valve actually reaches the commanded opening. P0405 is set when that signal drops below the minimum plausible value, typically under 0.1-0.2 V, which indicates a short to ground, an open signal wire, a missing 5 V reference or a failed sensor track. The ECM then runs the valve open-loop or disables EGR entirely.

Advertisement728 × 90

Symptoms

  • Check engine light with no obvious driveability change
  • Slight knock or pinging under load on petrol engines (EGR disabled)
  • Higher NOx at emissions test, possible test failure
  • Rough idle or hesitation if the valve is actually stuck open and the ECM cannot see it
  • Reduced power or limp mode on some diesel engines

Common causes

  1. Worn potentiometer track inside the EGR valve position sensor
  2. Signal wire shorted to ground, chafed on the EGR cooler or bracket
  3. Open signal or 5 V reference wire, or corroded connector pins
  4. Loss of the shared 5 V reference (other sensors on the same supply set codes too)
  5. Carbon-jammed valve parking the sensor below its learned zero point
  6. Faulty EGR valve assembly after overheating

How to diagnose

  1. Read EGR position in live data with key on, engine off: a closed valve normally reads 0.5-1.2 V or 5-15 percent. A reading of 0 V or 0 percent points to the circuit.
  2. Check the 5 V reference at the sensor connector with key on (4.9-5.1 V) and the sensor ground (under 0.1 V to battery negative). No 5 V: inspect wiring or other sensors sharing the supply.
  3. Measure the sensor: with the valve unplugged, potentiometer total resistance typically 3-6 kohm between reference and ground; signal to ground should sweep smoothly as the valve is moved. Jumps or dropouts mean a worn track.
  4. Check the signal wire for short to ground: unplug sensor and ECM connector, measure signal wire to ground; should be infinite. Continuity ECM to sensor under 1 ohm.
  5. Command the valve with the scan tool 0-100 percent and compare commanded to actual position; it should track within 5 percent. No movement with a healthy sensor circuit means the valve is seized.
  6. Remove and inspect the valve for carbon if the sensor reads low only at the closed position; clean or replace, then perform the EGR position learn procedure where the manufacturer requires it.

Frequently asked questions

Can the position sensor be replaced separately?

On most modern valves no, the sensor is integrated and the whole valve is replaced. A few older designs have a bolt-on sensor.

P0405 appeared with P0122 and P0112 at the same time. Why?

Those sensors share a 5 V reference. A single short on one sensor can drag the reference down and set codes on all of them. Find the sensor that is shorted.

Is it dangerous to drive?

No. EGR affects emissions and knock control, not basic engine safety. Repair before the next emissions inspection.

Related codes

P0406P0404P0403P0401P0402

Nearby codes in this group