Check engine P0420
 

Hi,
I know it is cat converter,but I dont know which one front or rear?
What next should I check?
Thanks.
Jaromir
2004 4 cyl.

RE: Check engine P0420
 

Typically it is the large converter under the car.

The code is stating the A/F sensor output located after the CAT is not what it should be when compared to the A/F sensor output located before the CAT. The computer has no way of actually testing the CAT.

As such could be an A/F sensor, the CAT, etc.

The EPA mandates a warranty of 8 years or 80K miles for the CAT's. If your car is still under this warranty period and the CAT(s) is bad the dealer must replace it for free under federal law. Read the owners manual and whatever emissions warranty info came with it.

RE: Check engine P0420
 

No warranty any more.Car have 91K miles.
Thanks

RE: Check engine P0420
 

If a CAT issue, typically it is the main one under the car.

RE: Check engine P0420
 

Should I first replace a/f sensor after cat?
Thanks

RE: Check engine P0420
 

There are trouble codes for all A/F sensors included after the CAT but the issue may be a sluggish reponding sensor that may not trip a code. Typically the A/F sensor before the CAT fails first.

Without further diagnositics would be just guessing.

The Toyota dealer or someone with a scanner that can actually output A/F voltages in real time can compare the A/F sensor signals before and after the CAT and compare.

The proceedure is to check the performance of the A/F sensors before and after CAT and if OK to replace the CAT.

Any leaks in the exhaust system?

RE: Check engine P0420
 

I dont think I have any exhaust leaks.
What do you think about magnaflow cat,muffler is stock.
Thanks.
Jaromir

RE: Check engine P0420
 

People seem happy with the Magnaflow CAT's. Not sure you will get more HP if that is what you are after. You will still have the rest of the stock exhaust system.

If you do get A/F sensors suggest either Denso or Toyota OEM. Replacing with Bosch has resulted on occation with A/F sensor trouble codes.

RE: Check engine P0420
 

Do I need any gaskets?
Thanks