OBD II diagnostic codes...what do they mean?

Question

I have a '03 Lancer ES. I had my engine light on and had it checked. I was told it was my O2 sensor so I got a second opinion to be sure and was told the same. I ordered the sensor and my brother in law installed it on my car before i could even open the package to make sure it was the right one. So i had a mechanic check and clear the engine coding. About 3 hours later the light came back on. On my invoice from the mecahnic, he listed the codes. whcich are PO135, loosely tranlates to O2 heater Bank 1 sensor 1; the other code PO421, warm up cat efficiantcy low. I just when to Auto zone for them to run a diaignostic and the code for the 'cat?' came up. Please someone tell me what these are specifcally pertaining to. Also, prior to the engine light initially coming on, there was a recall on the catalytic converter..so that was replaced...the light coming on shortly after that? What's going on with my car? I don't wanna shell out more money but my little girls ride in it.

Answer 1

From your narrative, I assume that the only code now is the P0421.
This is the PCM's identification of a failure to to meet expectations programmed into the PCM.
The Catalytic converter is not a computer component. But the law required that the car be able to tell when it fails. SO--- there is a routine programmed into the PCM that helps it to know when the Catalytic Converter is failing. the car has up-stream O2 sensors, and a down-stream sensor. When the computer begins to see that the rear sensor is "mirroring" the front sensor, the logic indicates that the cat is no longer functioning at a reasonable level. It will illuminate the "Check Engine" light.
At this point, it is important that proper diagnostics be performed rather than merely throwing parts (pronounced MONEY) at the car.
There are tests that are performed to test the oxygen sensors and the cat. If you replace the rear O2, and clear the codes, the problem MAY go away. But maybe not. The CAT may be the issue.
At this point, you may be money, time, effort and frustration ahead to pony up and have a LICENSED reputable smog repair and test facility run the diagnostics for the code. He/they can test the cat, O2(s) both up-stream and down-stream, as well as test the rest of the powertrain control to be certain that the car is in full Fuel Control.

Good Luck and Merry Christmas

Answer 2

its a possibility there may either be damage to the O2 sensor behind the cat when they replaced your converter. those things are VERY sensitive. in most cases, if you get a reading dealing with the cat, its usually coming from the sensor behind it.

Answer 3

obd11 code is a code that your cars computer puts out to confuse the average joe into spending lots of money to have there car repaired,bank one sensor one is your o2 sensor on the drivers side,the one located on the exaust manifold,change this one and go back to autozone and have your codes cleared,this should od the trick....