I have a 1999 LeSabre. I've just replaced both oxygen sensors and now I'm getting 2 codes; P0171 and P0134c. It gave me the P0134 twice, counting it as three codes? Where to go from here?

Hi! This is Bo with Car Genius at RepairPal! Well, that's frustrating! The P0171 and P0134 codes on your 1999 LeSabre suggest a lean fuel mixture and a fault with the oxygen sensor circuit on bank 1 sensor 1. You could check the wiring and connections on the B1S1 O2 sensor and then check for vacuum leaks, inspect the intake system for air leaks, and ensure the fuel pressure is within specifications. When I looked in tech forums at these two codes popping up together, a few of the fixes were the mass air flow sensor, the intake manifold plenum and the EGR just to name a few. You've got your work cut out for you. If the issue persists, further diagnostics by a mechanic may be necessary to pinpoint the exact cause. If you have any other questions feel free to call us at 877-913-1554! We'll be happy to find you a certified RepairPal shop in your area!