By
Jeff726, February 22, 2012
The mechanic at my work used his code scanner and the PO420 code came up. I have also noticed a dropoff in gas mileage the last few weeks since I have replaced the spark plugs and PCV valve. What should I try before spending hundreds of dollars at a shop?
A lot of things can throw this code. It means: Catalyst system inefficient.
Anything from bank1 oxygen sensor, bank2 oxygen sensor, MAF sensor and catalytic converter. How long ago (miles and period of time) did you change oxygen sensors? Oxygen sensor voltages should be measured if you want to diagnose the problem instead of throwing parts at the car.
If catalytic converter is indeed going bad, you will notice drivability problems like sluggish acceleration. Does your car burn any oil? If yes, how much?
Haynes manual has a section called Emissions where they detail diagnosis of oxygen sensors and MAF sensors. For starters you should go ahead and clean up MAF sensor (sits on airbox after the filter) with throttle body cleaner. Also doesn't hurt to clean up throttle body while you are at it.
In the nutshell, it's not easy to diagnose the emission system, but you don't have to shell out hundreds of dollars at the shop to diagnose. Most of this stuff you can do yourself.
If you find that O2 sensors are indeed bad, you can buy original ACDELCO or DENSO brand sensors from rockauto. They currently have the best prices. I just did an estimate the other day and it came out to about $110 for both sensors, direct fit OEM.
Hope that helps.
Need a bit more info:
What mileage are you at on the 2000 Corolla?
What PCV did you use - was it OEM or aftermarket?
What replacement plugs did you use - how did the old ones look?
Have you tried resetting the ECM and see if the code comes right back?
Need a bit more info:
What mileage are you at on the 2000 Corolla?
What PCV did you use - was it OEM or aftermarket?
What replacement plugs did you use - how did the old ones look?
Have you tried resetting the ECM and see if the code comes right back?
Just over 156,000 miles
Aftermarket PCV
I used plugs bought from the Toyota dealership nearest me. The old ones were fried
Will try resetting the ECM
A lot of things can throw this code. It means: Catalyst system inefficient.
Anything from bank1 oxygen sensor, bank2 oxygen sensor, MAF sensor and catalytic converter. How long ago (miles and period of time) did you change oxygen sensors? Oxygen sensor voltages should be measured if you want to diagnose the problem instead of throwing parts at the car.
If catalytic converter is indeed going bad, you will notice drivability problems like sluggish acceleration. Does your car burn any oil? If yes, how much?
Haynes manual has a section called Emissions where they detail diagnosis of oxygen sensors and MAF sensors. For starters you should go ahead and clean up MAF sensor (sits on airbox after the filter) with throttle body cleaner. Also doesn't hurt to clean up throttle body while you are at it.
In the nutshell, it's not easy to diagnose the emission system, but you don't have to shell out hundreds of dollars at the shop to diagnose. Most of this stuff you can do yourself.
If you find that O2 sensors are indeed bad, you can buy original ACDELCO or DENSO brand sensors from rockauto. They currently have the best prices. I just did an estimate the other day and it came out to about $110 for both sensors, direct fit OEM.
Hope that helps.
I have not replaced the O2 sensors ever. The car does burn oil though I cannot pinpoint how much exactly. I do not have any tools so I will have to find a friend to help me.
Checking PCV valve is easy enough. All you need is a wrench to remove it from the engine. First disconnect the vacuum hose that attaches to the valve, then remove the valve. If you shake the valve, it should rattle. If it doesn't that means it's clogged. Then you should replace it.
Also, what do you mean by plugs were fried? Do you remember their color, condition, any oil residue on them?
