2004 Chevy Trailblazer O2 Sensor P1133 Fault: Downstream Sensor Replacement Not Resolving Code
I own a 2004 Chevrolet Trailblazer and recently had the spark plugs replaced. After that, my vehicle triggered an O2 sensor fault with code P1133. I purchased a new Bosch downstream oxygen sensor from O'Reilly and installed it, but the service engine light remains on. Despite the replacement, the issue persists. I'm unsure what to do next—any advice or troubleshooting steps would be greatly appreciated.
Please confirm which engine you have (e.g., 4.3L V6). Code P1133 typically refers to Bank 1 Sensor 1, which is an upstream oxygen sensor, not downstream. You may need to return the Bosch sensor and get a genuine OEM or dealer-approved unit. Also, ensure that AC Delco spark plugs were installed—there's a significant difference between brands, and incorrect plug types can affect engine performance and diagnostic readings.