Emissions

P0404 — EGR Circuit Range/Performance Problem

Severity: medium Drive with care, to a shop

What P0404 means

The engine control unit compares the commanded EGR valve position with the actual position reported by the position sensor, and also watches how the engine responds when the valve opens. Normally the EGR system routes some exhaust gas back into the intake to lower combustion temperature and reduce NOx emissions. P0404 sets when the valve sticks, does not open to the commanded amount, or the sensor signal does not match the command.

Symptoms

  • Check Engine light on
  • Rough or unstable idle
  • Hesitation and weak acceleration
  • Stalling or stumbling at idle
  • Worse fuel economy
  • Failed emissions test

Possible causes

  1. EGR valve stuck or worn (carbon, failed actuator)
  2. Faulty EGR valve position sensor
  3. Carbon buildup or clogged EGR passages
  4. Wiring or connector problems: open, short or corroded terminals
  5. Leaking or blocked vacuum hoses (vacuum-operated valves)
  6. Rarely, a PCM software fault or failed PCM

How to diagnose

  1. Scan all modules and record the freeze frame data
  2. Check battery and charging system voltage
  3. Inspect the EGR wiring and connector for damage, corrosion or oil
  4. Compare commanded and actual EGR position in live data
  5. Test the position sensor's power, ground and reference voltage
  6. Remove the valve and inspect it and the passages for carbon; check that the valve moves freely
  7. On vacuum-operated systems, check hoses, solenoid and vacuum supply
  8. Clear the code and road test to confirm the repair

Common fixes

  • Clean the EGR valve and passages
  • Replace the EGR valve or its position sensor
  • Repair EGR circuit wiring and connectors
  • Replace damaged vacuum hoses or the control solenoid
  • Update PCM software if the manufacturer offers a fix

Questions and answers

Can I drive with a P0404 code?

For a short time, if the engine runs smoothly. If you get surging, hesitation or stalling at idle, have it checked soon.

Will cleaning the EGR valve fix P0404?

Often, when carbon is the cause. If the code returns, check the position sensor, wiring and the valve actuator.

Can I block off the EGR to clear the code?

That violates emissions rules and can cause an inspection failure. It is better to find and fix the actual fault.

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.