Understand how the ECU verifies flow
Depending on the engine, EGR flow may be inferred from air-mass change, manifold pressure, temperature, position feedback or a combination of models. The diagnostic strategy must be understood before interpreting one sensor value.
Record related boost, MAF, throttle, pressure and temperature codes. A problem elsewhere in the air path can prevent the expected response even when the EGR valve moves.
Compare command, movement and system response
Use a controlled actuator test where supported. Compare commanded position with feedback and observe whether air mass or manifold pressure changes in the expected direction.
If command changes but position does not, inspect actuation, wiring, vacuum supply and mechanical seizure. If position changes without the expected flow response, investigate blocked passages, intake deposits and sensor plausibility.
Inspect the complete air path
Check intake and charge-air leaks, throttle operation, manifold deposits and exhaust restrictions. On vacuum systems, verify supply, solenoid control and hose integrity under load rather than only at idle.
Electrical diagnosis should include reference voltage, ground quality, signal range and connector condition. Avoid replacing the valve from the code description alone.
Repair, validate and document
After repair, repeat the enabling conditions and confirm commanded and actual values. Clearing a code without reproducing the monitor is not a completed diagnosis.
Emission-control changes must comply with applicable law. The EGR service page explains the declared-use workflow for applications where calibration work is permitted.