How do downstream oxygen sensor readings affect catalytic converter monitoring and fuel control, and what issues can cause incorrect readings?

How do downstream oxygen sensor readings affect catalytic converter monitoring and fuel control, and what issues can cause incorrect readings?

• A. Downstream O2 sensor tracks catalytic converter efficiency to verify conversion; if sensors read incorrectly due to contamination or aging, ECU may adjust falsely; cause of incorrect readings: sensor contamination, poor wiring, exhaust leaks, excessive fuel or misfire.
• B. Upstream oxygen sensor readings track catalytic converter efficiency to verify conversion.
• C. Downstream O2 sensor controls fuel injection timing.
• D. O2 sensors do not affect ECU fuel control.

Answer: (A)