Greetings all,

I've received the following codes which the manual describes as follows:

12 - Battery Disconnect - direct battery input to PCM was disconnected within the last 50 Key-on cycles. This makes sense since I disconnected the battery for working on my idler pulley and belt.

But the ones I am concerned with are:

21 - O2S Stays at Center or O2S Shorted to Voltage - Neither rich or lean condition detected from the oxygen sensor input OR Oxygen sensor input voltage maintained above the normal operating range.

51 - O2S Signal Stays Below Center (Lean) - Oxygen sensor signal input indicates lean/air fuel ratio condition during engine operation.

Seems as though 21 and 51 conflict with each other. I did double check to see if I was getting these codes.

Could this indicate the sensor is bad?

I'm going to be replacing the whole pipe soon (including cat and muffler - thank you rust) so while I was down there I figured I might as well do something about this sensor.

Thanks!
10th

 

Pretty likely the sensor is bad or the wiring to it is damaged. I believe 21 means the sensor isn't cycling the way it should, and 51 means it's staying on the lean side. You have just the one pre-cat sensor, or is this a CA model with more than one sensor?

 

Looks like there is only one pre-cat. I do have an official shop manual, and double checked there's only one on the pipe.