2008 Buick LaCrosse P0420 and P0025 Check Engine Light Issue - Cold Start Only

Model: Buick LaCrosse Fault Code: P0025 Posted: 2019-08-29 23:32

I own a 2008 Buick LaCrosse Super with recurring check engine light issues. After replacing both upstream and downstream oxygen sensors, the P0420 code (related to catalytic converter efficiency) appeared frequently on Bank 1 but has since disappeared. Currently, I'm experiencing intermittent activation of the P0025 code, which triggers the check engine light only when starting the vehicle during a cold morning start. No noticeable performance symptoms or drivability issues are present as reported by the OBD2 scanner. The issue consistently occurs on first-starts in the morning and does not appear after the car has warmed up. I'm seeking advice on potential causes and troubleshooting steps for this specific P0025 fault, especially related to cold engine conditions.