The computer sees too little EGR flow when it commands the valve open. The driver may notice engine knock under load or only the engine light.
Causes vary by car. Test before you order a part.
Likely causes, most common first
- Carbon blocking the EGR passages
- Sticking or faulty EGR valve
- Vacuum hose or control solenoid fault
- Faulty EGR sensor
Parts usually involved
- EGR valve Find at suppliers
- EGR passages Find at suppliers
- Vacuum hose Find at suppliers
Test before you replace
Inspect the valve and passages for carbon, then command the valve and watch the engine reaction.
General guidance for generic OBD2 codes. Always follow the maker's procedure for the car in front of you.