2003 Corolla - P420 Help Please

[cparks3019]

Car chokes out when it warms up. This started about a month ago, the car was below a quarter of tank and i had slight power loss. Filled it up and it stopped. For the next week the car ran fine only having problems when it was low on gas. Now it will crank up and purr like a kitten until it gets warm then it spudders then chokes out and wont start again until it sits. i assumed fuel problems. checked gas tank and inspected fuel pump no issues there that i can see. i had been told the IAC was going out about a year ago and was getting a P505 code along with the P420. changed IAC and unplugged battery to reset ECM. no fix. noticed a decent amount of oil in my sspark plugs. cleaned out the chambers and replaced spark plugs along with the oem valve cover gasket. no fix... ive gotten rid of the P505 but not P420. ive heard everything from fuel inectors to clogged catalytic converter and even that there might be a recall on my ECM from the factory. Im already in the hole a good bit of money and if i dont fix this soon ill be losing more than just money without my car. I need help guys.

2003 toyota corolla ce 1.8L 1ZZFE 350k

 

[IFMJohn]

Here is the deal. To understand what you're diagnosing, you have to understand what the computer is seeing.

P0420 indicates that the computer is seeing that the cat is not cleaning the exhaust as well as it should be. There is an O2 sensor before and after the cat.

So, if the first O2 sensor is not working properly, that code appears because the computer is not seeing as much of a change in emissions across the cat that it expects to see. The same theory goes with the downstream (after CAT) o2 sensor.

Also, the cat could flat out be bad.

Toyota set their emissions perameters very tight in the computer (much tighter than required by the EPA). This causes issues once parts start to wear and get old as they no longer work as well as they once did (but they still work). To fix this, toyota did release an ECM calibration update that changes the range that the ECM expects to see from the o2 sensors.

Go into toyota and ask them to check for ECM updates. That may very well fix your issue. I couldn't see them charging more than an hour labor if an update is needed.

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