Fault code P0402 – a step-by-step guide to diagnosing and fixing it

Error code P0402 is displayed and the check engine light is on - what does this mean?

The OBD system detects an excessive flow in the exhaust gas recirculation system (EGR system). The DTC P0402 means "EGR Flow Excessive Detected" and indicates that more exhaust gas is being recirculated than expected by the engine control unit. This trouble code may have slightly different names for different manufacturers, but always refers to the EGR system.

What causes can this error code have?

• Defective EGR valve (stuck in open position)
• Dirty or blocked EGR valve
• Defective EGR position sensor
• Damaged vacuum hoses to the EGR valve
• Faulty EGR control in the engine control unit
• Defective EGR temperature sensors
• Leaking EGR seals
• Blocked EGR cooler
• Loose or corroded plug connections

What symptoms occur in parallel with fault code P0402?

• Check engine light: Lights up continuously or flashes
• Uneven idling: Engine runs unevenly at idle speed
• Loss of power: Reduced engine power during acceleration
• Increased fuel consumption: Poorer consumption values
• Knocking noises: Metallic noises from the engine compartment
• Starting problems: Difficult starting, especially when the engine is cold
• Black smoke: Dark exhaust fumes from the exhaust pipe

How to fix the problem of error code P0402?

• The repair requires a systematic diagnosis of the EGR system to identify the exact cause.
• Remove the EGR valve, clean thoroughly or replace completely if defective
• Check all vacuum hoses and connections to the EGR system and replace damaged parts
• Test the EGR position sensor and replace if the readings are incorrect
• Check electrical connections and plugs on the EGR valve for corrosion and clean
• Dismantle and clean the EGR cooler or replace if clogged
• Check engine control unit for software updates and reprogram if necessary
• Carry out a complete EGR system diagnosis with a professional diagnostic device