Hey everyone, today has been a crazy day for my SC. I had terrible misfire issues for the past 2 months, and a code 21 popping up. Now, today my buddy and I wired in a denso universal o2 sensor up front right behind the front wheel. I was told code 21 means left bank main o2 sensor. AKA driver side main o2. So we replace that, and I still have awful misfire and the code. Redphoenix told me to get coil packs. I did. Misfire GONE!

BUT THEN, code 21 STILL comes on....its not instant either it takes a few minutes sometimes up to about 15 minutes to come on. Most importantly there is no more misfire. I still have no idea why my CEL will not go off...can anyone please chime in here.

 

check to make sure that all the wires on the o2 sensor are all intact, i have a frayed wire on my car and it's throwing a code 21 as well.