P0400 – Exhaust Gas Recirculation Flow Malfunction

Meaning:

When there’s either an insufficient or non-existent amount of exhaust gases entering the cylinders, the P0400 happens
The P0400 is triggered when there’s either an insufficient or non-existent amount of exhaust gases entering the cylinders

There’s either an insufficient or non-existent amount of exhaust gases entering the cylinders.

Main Symptoms:

  • Increased NOx emissions
  • Increased combustion temperatures

Possible Causes:

  • Exhaust gas recirculation (EGR) passage is plugged
  • EGR solenoid is faulty
  • Wiring or harness to EGR solenoid is faulty
  • EGR valve is faulty
  • Either vacuum lines are damaged or disconnected from EGR valve or EGR valve solenoid

Diagnostic Steps:

  • With a bidirectional scan tool, open and close EGR valve while the engine is running. If the engine stumbles then there’s a wiring problem
  • If the engine doesn’t stumble but it dies then the ports are plugged
  • After the above visually inspect all hoses, vacuum lines, solenoid and solenoid harnesses for damage
  • Using the scanner, check solenoid voltage to ensure its within normal range
  • If all the above check out replace EGR valve

Read More: OBD2 Codes List: Meaning, Fixes, and Free Download