I had 2 codes, a P0403 and a P0431. Even then extremely poor gas mileage. The SUV ran fine. No problems starting, accelerating, at idle, etc. I replaced the EGR solenoid. The car runs the same but is now getting much better mileage.
I reset the light and after a few days it turned orange again. I checked it with a code reader and it came back as P0431. What do I do? Replace one or all of the 02 Sensors? Do nothing as its driving OK and assume the only problem is with the exhaust? Will I do damage if I do nothing?
The best way to check this trouble code out is to have someone check out the O2 sensors with a scanner.
The most common cause of this code is that the sensor becomes contaminated and is slow to respond to the changes to the exhaust gases (lazy sensor). The other problem is that the sensor heater is faulty. In some rare cases the catalytic converter is going bad and would need to be changed.
Using a scanner can check all four of the O2 sensors for proper operation so you can be sure to change the correct one.