P0401 (EGR Flow Insufficient) – Vauxhall CDTi patterns
On CDTi engines, P0401 is rarely just “dirty EGR”. Prove command vs effect.
Why it clusters with DPF and boost codes
EGR flow is part of emissions control. When DPF loading is high or boost control is off, the ECU may reduce EGR and your measured flow won’t match expectations.
What to check first
- Check for intake restrictions and boost leaks (plausibility).
- Verify EGR command and MAF response — flow should change when EGR is commanded.
- Inspect the cooler/pipework for blockages where relevant.
Make it Vauxhall-specific
Start at the manufacturer hub to match the code to the engine family (EcoTEC petrol vs CDTi diesel) and the common platform patterns.
Open Vauxhall/Opel diagnostics hub →