It’s what Honda terms as intermittent failures. It means a system may have had a failure, but checks OK now (or later).

On both of your primary cat converters; respectively, there are separate air/fuel ratio sensors and secondary heated oxygen sensors.

The respective secondary Heated Oxygen Sensors (HO2S) detects the oxygen content in the exhaust gas downstream of the warm up three way catalytic converter and sends signals to the ECM/PCM (car’s computer). To stabilize its output, the secondary sensor has an internal heater. The ECM/PCM compares the HO2S output with the Air/Fuel ratio sensor to determine catalyst efficiency. The secondary HO2S is installed downstream of the warm up three way cat.

The ECM/PCM has detected efficiency levels below a set threshold and is setting your trouble code(s).

On some other makes of cars before, some people have reported that they were able to change the downstream heated oxygen sensor and have the code(s) go away. I heard many Honda techs say that won't work. I am not suggesting you do or don't do that. I am just throwing info. out there.

Catalytic converters are expensive.

Honda dealers have their Honda Diagnostic System (HDS) hardware/software that can be used to try to analyze cat efficiency; but, not everyone wants to pay the diagnostic fee.

 

[QUOTE=Millie_EDX;304225]I have been driving the car for awhile, the Check Engine Light turns on/off every so often. It was on about 3 weeks ago then turned off a week following that, and it returned


typically if you are having both banks throw a catalyst code, you have a clogged cat. If you don't have one common cat before both sensors, like if both were downstream codes, than you need to get a volt meter and ohm out both sensors, and your knock or cam sensor, (I can't remember which one affects catalyst readings) but the odds of both o2 sensors failing are hella low. My .02 cents