P1221, P1271, P1635 Fault Codes on 2002 Chevrolet Trailblazer - What Do They Mean?
Hello everyone, I recently replaced the fuel pump on my 2002 Chevrolet Trailblazer due to severe corrosion in the sending and return lines. Later that evening, the service light illuminated, so I connected a OBD-II scanner and retrieved three diagnostic trouble codes: P1221 (Manufacturer Control Fuel Air Metering), P1271 (same issue as P1221 but with different code identifier), and P1635 (Manufacturer Auxiliary Input/Output). I'm trying to understand what these specific fault codes mean in the context of my vehicle. Is there a direct connection between the fuel pump replacement and these codes? Could the corrosion or installation process have triggered them? Any clarification on these codes would be greatly appreciated. Thank you for your help!
P1221 refers to a fault in the fuel air metering control circuit, typically related to fuel delivery or sensor feedback. P1271 is often linked to an issue with the accelerator pedal position (APP) sensor 1-2 correlation, suggesting potential misalignment or signal inconsistency between sensors. P1635 indicates a problem with the 5-volt reference circuit for auxiliary inputs/outputs, which may affect various electronic systems. These codes could be related to wiring or grounding issues post-fuel pump replacement.