The exhaust gas recirculation system sends a controlled amount of exhaust gas back into the intake to reduce emissions. When the EGR valve sticks, becomes heavily contaminated or is affected by an electrical fault, the engine can develop a range of running problems.
Common EGR symptoms
Possible symptoms include hesitation, rough idle, loss of power, excessive smoke, poor fuel economy and an engine warning light. Some vehicles may enter a reduced-power mode when the ECU detects that commanded and actual EGR flow do not agree.
Carbon build-up
Diesel intake systems naturally collect a mixture of soot and oil vapour over time. This can restrict passages or prevent the EGR valve from moving freely. However, carbon deposits should not automatically be treated as the only cause of the fault.
Electrical and control faults
Many modern EGR valves contain position sensors and electric actuators. Wiring damage, poor connectors, sensor faults and ECU control issues can all produce EGR-related codes. Vacuum-operated systems can also suffer from leaking hoses or failed control solenoids.
Why live data is useful
Comparing commanded EGR position, actual position, air-flow readings and boost data can help establish whether the valve is responding correctly. An air-flow meter or boost leak can sometimes create symptoms that appear similar to an EGR fault.
Cleaning or replacement?
Whether cleaning is suitable depends on the condition and design of the valve. A mechanically damaged actuator or failed position sensor will not be repaired by cleaning. Diagnosis should come first so the repair matches the actual failure.
For diesel running faults, EGR-related warning lights and loss of power, see our diesel emissions diagnostics service or book your vehicle online.
Still not sure what is causing the problem?
Symptoms can overlap between several faults. A proper inspection and diagnostic process is usually cheaper than replacing parts based on guesswork.