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Discussion Starter · #1 ·
I have a 2000 Corolla throwing these dreaded EVAP codes. I tested the VSV and it was bad, so I replaced the whole charcoal canister. I also replaced the gas cap and recently did a smoke test for leaks and found none. The purge valve at the front tests good as well. But I'm still getting the codes after all of this work.
Any ideas? I'm at a loss.

When I remove the hose from the inlet side of the purge valve in the engine compartment, I can blow air into the rear of the car. Should this be possible when the car isn't running, or does that mean there is a leak? I can't blow air into the valve itself (which makes sense).

I need to have it fixed for Connecticut emissions.

I'm also getting a P0420 but I assume since that indicates the catalytic converter it is a separate problem (perhaps caused by my EVAP leak creating a rich environment).

Any help would be appreciated.
 

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2005 Celica GT
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Did you reset the codes and did they come back?

I'd check to make sure everything on the canister is attached properly.
On 3 cars I've worked on with P0420, all of them had a bad downstream oxygen sensor. Do a voltage test on the sensor to make sure it's not acting up.
 

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Discussion Starter · #6 ·
Thanks for the advice! I did clear the codes and they all came back. This week I'm going to hook up the smoke machine again and see if there are any leaks. I suspect the fuel tank fill check valve. I've heard they crack sometimes.

I checked the P0420 by checking for decreased vacuum in the manifold while the engine ran (this would imply a blockage), and by checking the ECM voltage readings from both O2 sensors. No decrease in pressure, and the upstream sensor was fine. The downstream is harder to determine. I don't have an oscilloscope, so it's tough to see if it is keeping the line or not. It should be hovering around .5 volts, but if it isn't, how would I know if that is the sensor or the Catalytic Converter underperforming? I think I'll check the Cat temperature at inlet and outlet, but I suspect the cat has gone bad from the engine running rich from the EVAP problem. The check engine light bulb is burned out, which means that the EVAP problem could have been there for YEARS without them knowing about it.
 

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I usually tell that the downstream sensor is out by not seeing any voltage through an OBD2 reader. They usually just say "waiting for voltage". Obviously that's the easy fix, if yours is not performing properly I'm not sure how to check that.

An RX300 I fixed with all the codes as you ended up needing a downstream 02 sensor and a charcoal canister. Problem was that I needed to replace both before a single code would disappear.
 

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I had both of those codes over the summer and failed my emissions like 3 times. On the evap system codes P0440/P0442, I only bought a new OEM fuel cap from Toyota. Then on my P0420 code, I took the easy road and did a spark plug non fouler mod.
 
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