o2 sensor swap

[slo_k20]

I have a CEL for a bad primary o2 sensor. I want to know if both of the sensors are the same, and if I could just put the secondary sensor in place of the first temporarily to make the car run right, because it's running lean now. It won't affect the performance if there's a bad secondary sensor right?

[AUTiger]

definitely not the same, the primary sensor is an a/f sensor. And with a bad primary, you would be running rich and not lean.

[4angrybadgers]

AUTiger is correct, the sensors are different. If the ECU can't get a good measurement from the primary, it defaults to a certain set of fuel maps that are pig-rich (it's safer for the motor to run rich instead of lean if the ECU can't monitor the A/F ratio).

A malfunctioning/missing secondary will not affect performance or gas mileage, you'll just have a constant CEL.

[slo_k20]

definitely not the same, the primary sensor is an a/f sensor. And with a bad primary, you would be running rich and not lean.

So why am I getting one CEL for a bad primary sensor and another for Fuel System Too Lean?