Exhaust leaks that can cause a P2187 code are typically found before the upstream oxygen sensor. Common locations include:
1. Exhaust manifold gaskets or cracks
2. Exhaust pipe flange gaskets
3. EGR tube connections
4. Turbocharger mounting gasket (if equipped).
Small leaks can be difficult to see or hear, so a mechanic may use a smoke machine or propane enrichment tool to pinpoint their exact location.