I recently got the infamous CES light throwing a P0430(cat bank 2 inefficiency) on my 2004 330xi with 182k miles. I probed the post cat and pre cat sensors using torque pro, and to my untrained eye all readings from the o2 sensors are as to be expected, post cats are steady but react to changes in throttle, and pre cats are oscillating high low as expected. The pre cats dont seem to be too in sync however... Mostly it looks like the bank 2 lags a little but the frequency is the same. Also when I do the test results, sometimes one of the o2 sensors throws an error but i forgot to write it down. I'm not exactly sure what steps to take to be honest, as this is my first car and I am just getting into car mechanics. Any help would be greatly appreciated!!
I guess people are using spark plug adaptors to pull the post cats sensors up out of the way then get the car smogged
Take care of the o2 sensor issue before replacing a cat. Pre cat sensors won't be synchronized. That is normal. Similar switching frequency is also good. O2 sensor replacement interval is 100k. You are almost double that. Probably a good idea to replace them all.
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I just got the car used(for free from a friend) and he has no idea if the sensors were ever replaced, so the current ones might only have 80k miles or even less. One thing I notices was that the post cats were sitting at around .8volts. Does BMW have a voltage bias, or is it actually that rich? Maybe the air filter needs to be replaced?
The first step is to replace the pre-cat sensors.
The car makes it possible, but the driver makes it happen.
Jim Levie, Huntsville, AL
I replaced the air filter and no light and the engine isn't running as rich.. we'll see.
Lazy or bad pre-cat O2 sensors will cause the engine to run rich. Which if not corrected by replacing the sensors will eventually cause the catalytic converters to fail from overheating. The post-cat sensors are in a more benign environment and rarely need replacement. So replace the pre-cat sensors now!
The car makes it possible, but the driver makes it happen.
Jim Levie, Huntsville, AL
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