2002 ES300 - 252k miles
Throwing engine codes:
P0420 - Catalyst Efficiency Bank 1
P0430 - Catalyst Efficiency Bank 2
P0440 - EVAP System Malfunction
P0446 - EVAP Vent Control Circuit Malfunction

There is a sizable exhaust leak in the flex pipe.

I suppose I could need 2 catalytic converters and a gas cap, but it seems strange to me that I would get codes for both banks (P0420 & P0430) at the same time. I know an exhaust leak can cause these codes IF the leak it located before the downstream sensor, but if I’m aware of all the O2 sensor locations, the flex pipe is past the last one.

Has anyone else experienced these codes being grouped together at the same time? Is there a chance, given the location of my flex pipe, that the leak is throwing off my readings?

Thanks in advance!

EDIT: In addition, would adding downstream o2 sensor “spacers” trick the CPU into clearing these cat codes even if the cats are in-fact bad?

 

An exhaust leak downstream could absolutely cause these codes. It’s introducing unaccounted oxygen to the exhaust gases that pass the downstream O2 sensor (B1S2). Get the exhaust leaks fixed and test again.

 

thanks for the quick reply!
I may be mistaken, but isn’t the flex pipe beyond all o2 sensors? I know there’s a 3rd cat in the straight pipe but I couldn’t locate any downstream sensors beyond the flex pipe.
thanks!

 

There is two main catalytic converters, one for each exhaust manifold right after the Upstream Air/Fuel sensor. Then there is a 3rd clean up cat after the flex pipe (see above), but before the downstream O2 sensor. If there is an issue with the efficiency of the catalytic converters, it will be detected downstream by the rear O2 sensor.

Now that I think about it, extra oxygen shouldn’t cause issues with the catalytic converters cuz it would actually help clean up the exhaust gases.

Usually the P0420 and P0430 means that the cat is not cleaning the exhaust gases and letting them through. The rear O2 sensor would then be bouncing between Lean and Rich signals way too fast which is what sets the code. In a normal condition, the rear sensor moves much slower between Lean and Rich than the upstream sensors which means the exhaust gases are clean.

If you have extra oxygen from an exhaust leak, then the rear sensor would be pegged at Lean (0 volts) and you may see a P0136 (O2 Sensor Circuit Bank 1 Sensor 2) fault code. That’s exactly what’s happening to my leaky exhaust system right now.

 

My car finally arrived. My original plan was flying there and drive back. Looks like I should be safe to use transportation company due to this issue. 400 miles, guess the chance of this happen to me is very high. : (

 

Feel bad for all the owners with the CEL issues

For what its worth I have not had any issues with my rear mufflers disconnected and they have been like this for over 1000km (600 miles).

 

...........

 

I had...HAVE....the 2 cat codes and had a leaking flex pipe. A shop welded in a new flex pipe, cat codes came back anyway.

The defoulers (spacers, etc.) do work in my case, so no codes.

 

SA Call this morning. It was exhaust leak and need to replace two gaskets. Waiting for the part now.

 

Good to know I am looking at used ES's for a friend.