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2001 Town & Country 2WD 3.8L - P0455 and P0420 Codes: Evap Leak and Catalytic Converter Issues

Model: 01 town n country 2wd 3.8 Fault Code: P0420 Posted: 2016-07-30 17:11

I've been experiencing the P0455 evaporative emission system leak code for nearly a month. I replaced the gas cap, but after the replacement, the purge valve light came back on. A smoke test revealed smoke escaping from either the EGR valve or the transducer — suggesting a possible purge line issue. However, today the check engine light returned with a P0420 catalytic converter efficiency code, while the evap-related code (P0455) no longer appears. This is confusing because I had my catalytic converter inspected previously and was told it was functioning properly. I'm now concerned: why does the P0455 code disappear after a month of recurring issues, only for a new P0420 to appear? Given that the vehicle has been in regular use and I have an inspection appointment tomorrow (last day otherwise), I need clarity on what might be causing this shift. Is it possible that the P0420 is triggered by a different underlying issue rather than a failing converter?

Related fault codes
P0420P0455
Comments (3)
Anonymous 2016-07-30 17:37

Can you confirm who performed the catalytic converter inspection and what tests were conducted? Smoke entering the intake manifold suggests that the purge valve may not be properly seated. If applicable, check the NVLP (Negative Valve Lift) component as well. As for the persistent P0455 code — it might take multiple successful test cycles to clear it. The issue could be intermittent; ensure all monitors are set to 'ready' or 'complete'. Also, please confirm: do you ever refill the fuel tank when the pump shuts off? This can affect evap system readings.

Anonymous 2016-07-30 17:44

That's exactly what I'm seeing — the P0455 code vanishes after a month of recurring issues, and now I have a P0420 code. The catalytic converter was supposedly fine during inspection, but this new code is causing real concern. My urgency stems from having an inspection appointment tomorrow — if it fails, I won't be able to drive the vehicle legally.

Anonymous 2016-07-31 08:44

I suspect your inspection is due in July. If the check engine light is on and P0420 is present, the catalytic converter monitor is likely not ready — this could result in a failure during inspection. Many dealerships issue a rejection sticker, extending the repair window by 10–15 days. You should have your technician investigate the P0420 code thoroughly or use an OBD2 scanner to review live data such as pre- and post-catalyst oxygen sensor voltages, freeze frame data, and monitor status. If you even have a sticker, check its details — it may provide insight into the inspection outcome.