disallow wrote:Hi SMJ,
I've had a nagging P0430 code for the last 6 months or so.
In your experience, can this be caused by a bad secondary O2 sensor? Only reason I ask is that when I check the voltages at 2000rpm, the voltage on the rear O2 sensor on the one side is all over the place, from 0.1v to 0.9v, but the Front sensor seems to be fine, at a stable 0.6v.
I've never changed the rear sensors, but did the front sensors about 30k miles ago.
Everything else seems normal. Performance, exhaust smell/appearance, fuel economy, etc. But I've also heard the horror stories of degraded catalysts getting sucked into the exhaust valves... Would rather avoid that...
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It's hard to determine catalyst efficiency by scan tool testing as there are a lot of variables. The general logic of catalyst efficiency is the observance of the rich-lean cycling frequency of the oxygen sensors; the rear sensor should have about half the cycling frequency of the front. If the front sensor is an air/fuel sensor, rather than an oxygen sensor, it makes it tougher being that air/fuel sensors run in a much narrower band, as I stated in the previous post. There are also a number of other values that the ECM looks at during it's determination of how efficient the converters are working, which is why it's a matter best left to the ECM. Usually if there is a problem with the sensors, the ECM will see it and trigger a sensor failure code and/or a catalyst efficiency code; in that particular case, one would ignore the catalyst code, address the sensor code, erase all codes and then see if the catalyst code re-sets. Same would go for any other code (such as a mass air sensor code) set with a catalyst efficiency code. Air/fuel sensors can be very tricky to determine if they are operating properly if you are graphing them in the same scale as you would an oxygen sensor; if you do, it often looks like the sensor is doing nothing or very little, whereas an oxygen sensor can range up to 1.1v and as low as 0v. Without other codes or exhaust leaks, it is usually the upstream catalytic converter that is at fault when a P0420/P0430 DTC is set.