2003 VW Jetta P0420, P0442, P2181, P0171 - System Too Lean Bank 1: What Components to Replace?

Model: 2003 VW Jetta Fault Code: P0171 Posted: 2018-02-23 17:21

I own a 2003 Volkswagen Jetta with 249,000 miles. The car runs smoothly overall, but I've noticed the coolant reservoir has been low twice in the past two months, triggering the warning light each time. I promptly refilled it and the engine has run fine since. However, I'm now seeing several diagnostic trouble codes: P0420, P0442, P2181, and P0170 (System Too Lean Bank 1). Can anyone clarify which components should be inspected or replaced? Specifically, should I replace the oxygen sensor (which one?), the catalytic converter, or the air filter? Any guidance on troubleshooting these codes would be greatly appreciated.