p0420 code gmc 2003 1500 sierra 5.3L

Question

what can i check for this code only?

Answer 1

Hi there,

To check the catalytic converter on bank 1 you need a scan tool that can watch the rear O2 sensor output. If the converter isn't working properly, then the sensor voltage will either never change or change very rapidly. If the converter is good, then you will see nice smooth transition on the voltage. Like rolling wave forms VS a choppy sea type of wave pattern