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Discussion Starter #1 (Edited)
I have the infamous P0420 code on my 02 Camry I4 2.4L on and off for some time. I have bought wireless ODB II reader with Dash Command on iPhone/iPad to check AF/O2 sensor readings and fuel trim. I was able to get away with it after resetting the code. Now it's at 160K and the P0420 wouldshow after a mere 30 miles. :headbang: So I went ahead and replaced the AF sensor first. All other readings are good including Long Term Fuel Trim (-3%) and Short Term Fuel Trim (-7% to +10% jumping as it should).

So it's time to replace the cat.

1. Disconnect the negative battery cable. Important! and move it out of the way.

2. Unhook upstream AF/O2 sensor cable. Just press really hard on the back side of the harness and pull the O2 connector out.

3. Remove the serpentine belt and remove the alternator. One of the exhaust manifold nut is right next to it, so it has to be removed first. Use 19mm socket and a pipe to push down (clockwise) to create slack in the belt, then slide off water pump pulley. Alternator is secured by two mounting bolts. See photo below.

And a better view for the lower bolt.

4. Jack up the car and loosen the exhaust manifold outlet flange nuts. They are really tight but I have a good impact gun.

5. Now on the lower side of the exhaust/cat, there are 5 mounting bolts, 3 on the passenger side, 2 on the driver side. Loosen and remove them. They are tight too, so use my 18 inch breaker bar with suitable extension.

Driver side 2 bots

6. Now remove the heat shield on top. A black dog bone mounting bracket is in the way, so remove it too. Just two 14mm bolts to secure the mounting bracket.

7. Remove the upstream AF/O2 sensor. Be sure to use O2 sensor socket as I am reuse mine. It's just one month old Denso.

8. Now 5 nuts to the engine with a long extension.

Close look at them.

9. Now lift gently of the cat out of the car. Some view of the engine with exhaust manifold removed. You can see my valves have white residuals on them, but otherwise they look good. Clean up the gasket area carefully and outlet side gasket. The new cat comes with new gaskets and hardware.

10. Remove the OEM heat shields and install them on the new cat. The new cat is an Eastern Catalytic Direct Fit ECO III Convertor, but the fit is not very good. It took me a little wiggling to install the heat shields.

11. Loosely attacked the mounting brackets to the new cat and lift it back into the car. The direct fit doesn't really fit the mounting holes on the engine/trans at all. I can only tighten the trans side two bolts, but for the engine side 3 bolts, I can only use 2, with one tighten side way to the bracket. I guess that's how after market cats are manufactured cheaply.

12. Install the rest pieces... I also took the alternator apart while it's out and exam the bearing and alternator brush. They are still good after 160k. So they are going back as is.

13. Start your engine and check leaks. There is a sticker on the new cat box with big warnings on properly break in the new cat. Here are the steps. Start the engine, warming up the engine to normal temperature. Press down the gas pedal and hold RPM to 2500 for 2 minutes. Let it cool down and check leaks again. There was strong burnt smell from the cat and some smoke too. They were oil residuals on the metal, so don't be too alarmed with the smoke.

14. Reset the check engine light and give it a test spin.

Overall it took 3 hours; maybe another hour to check exhaust leaks and cleanup. My cat monitor was ready after only 15 miles and O2 readings are good now, so I am happy... Just wish the fit could be more precise.:lol:

Super Moderator
2005 Corolla CE
14,606 Posts

Great DIY and thanks a lot!

2003 Camry LE 2.4L
107 Posts
I want add to if I could. I was able to remove the catalytic converter without removing the Alternator. I used one 12 mm offset wrench to remove the bottom left hand nut. This nut is hard to reach with regular wrench socket.


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