What could be the problem with my 01 Mazda Protege?

A

Alex

New member
I got a check engine light. When the an auto parts store the get a code pulled. I got PO421 code. According to a website from the internet it is 1 of 3 things. My cat converter which was replaced a couple 1000 miles ago. My spark plugs which are fine. And my front O2 sensor. I believe it is my O2 sensor. My car eats gas like crazy which is preventing me from driving it. Which further makes me believe its my O2 sensor. Any insight or advice would help. Thank you.
 
Sounds like you are on the right track with a bad o2 sensor. When they do go bad (their signal stops oscillating fast enough) the computer defaults to a "limp" mode. This is because the sensor is not providing accurate enough data for the computer to determine correct air/fuel mix. So, it defaults to a mode providing a rich enough gas mixture to accommodate most driving conditions, but this also provides too much gas for many driving conditions. The result is you are running rich, using too much gas, and are ruining you new cat. (it works overtime to try and burn all the unburned fuel due to the rich mixture) Get the o2 sensor swapped out asap.
 
I would say your 02 sensor because it tells the computer how much gas to feed your engine and if it is not giving the right info then the computer gives the gas the 02 sensor is asking for
 
Back
Top