Just got the ses light

[Silver2000V6]

I went to autozone and had the code scanned and it was:

DTC P0420 Catalyst System Low Efficiency

I had a 3" Catco installed a few months back. Does this mean I need to get O2 simms?

[12secondv6]

I get the same thing, actually code 0421
I dunno what the hell it is but I just plug my scanner in as I drive and hit clear.
I tend to get it more often when I drive in hot weather.
Anyone got more info on this??

[Shadly]

Well, you've officially achieved the flow you wanted. Flow = cool. It's not enough temp at the back of the cat to heat up that O2 sensor. Might have to go with a sim to get rid of that code.

[strange_trp]

yeah sims would probably be the only way to keep your cat and not see the light. or you could go into the eeprom and set wider acceptable parameters for the cat efficiency monitor.

[Silver2000V6]

Thanks for the help. Guess I'll be looking into sims in the near future.

[nyclaidback]

got the same SES light as u,because of catco highflow cat 3"... my mechanic scanned it says the tempearture the 02 sensor detects is not correct, thats cause air flows 2 fast trough the cat..he says i need 02 simulator

light doesnt really bother me im used to it..

[P-nut-]

Here's the 420 info.

DTC0420.pdf

I just let my light stay on and eventually it went away. Never came back on after the new cat.

[strange_trp]

to be technically accurate, it is not the temperature of the post-cat O2 sensor the PCM is looking at, but the amount of voltage generated by that sensor (based on the amt of oxygen passing by it in the exh system.) the temperature will be controlled by the O2S heater circuits in the PCM and will generate different codes than a sensor that is producing voltages that stay out of range too long or don't change voltage output to PCM as the pcm expects them to. the codes you're getting (p0420?) is related to O2S output, not temperature as was suggested in earlier post. sims should solve your problem. if the sensor is not too far out of range, the pcm may take care of the light itself by adaptive learn but most likely not. get some sims or a smaller cat...

[Dan90RS]

Aftermarket cats and OBDII do not go well together. I've seen many many "Catalyst Low Efficiancy" codes thrown with aftermaket cats.

For any of you lower milage guys, keep in mind that the cat is warrantied either 7yr/70,000 or 8yr/80,000....as long as the cat is factory, it can be replaced free.