Bought a 2007 Kia Sedona w/ CEL on (P0420). What are my options?

OBD-II trouble code P0420 indicates a possible fault with your Kia Sedona's catalytic converter. The actual description for trouble code P0420 is "Catalyst System Low Efficiency". With a P0420 it is very important to properly diagnosis the vehicle's entire emissions system.

P0420 may be a false code if other emission problems exists; particularly, an incorrect air/fuel ratio. OBD-II P0420 basically says the computer thinks there is a problem with the CAT. It bases test results on how well the CAT reduces emissions. Using the front oxygen sensor your Kia's engine control unit (ECU) takes an oxygen reading before the CAT, and using the rear oxygen sensor, a reading after the CAT. If the computer senses that the reduction in CO after the CAT is not significant, it triggers a P0420 fault. What we have to keep in mind though, is that in order for the CAT to work properly, air/fuel mixture must be precisely adjusted to 14.7/1. Any fault which could alter air/fuel mixture can potentially cause a P0420 trouble code fault. It is not recommend to suspect a bad catalytic converter until the rest of the emission system(s) have been diagnosed for proper operation.

We recommend checking your Kia's front and rear oxygen sensors; using a professional multimeter preferably one that will show wave patterns. When doing this test while your Kia is warm and running in closed loop mode, the oxygen sensor waveform reading before the catalytic converter should fluctuate between .1 and .8 volts. The O2 sensor waveform reading AFTER the catalytic converter should be fairly steady, anywhere near .45 volts. If the rear O2 sensor has no reading, replace the sensor. If the voltage reading is above .45, the CAT is not able to reduce emissions efficiently. After ensuring proper air/fuel ratio and correct functioning of other emission related systems, suspect a defective catalytic converter.

As far as applying for CAP, unfortunately a vehicle is not eligible for CAP repairs when having just been purchased.