According to Au7o's research across NHTSA recalls, manufacturer TSBs, and owner forum reports, the 1997 Pontiac Bonneville has 9 documented known issues, with 3 rated critical. The most serious are Plastic Upper Intake Manifold (Plenum) Degradation and Coolant Ingestion (3800 Series II) ($400-$1,100 repair), Bonneville 3800 V6 Lower Intake Manifold (LIM) Gasket Failure ($400-$1,200 repair) and Crankshaft Position Sensor / Ignition Control Module Failure Causing Stalling and No-Start ($150-$500 repair). Across all issues with published estimates, repair costs range from $30 to $3,200. DIY maintenance guides at au7o.io.