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Was that FFD (Freeze Frame Data) when the DTC set or just what you pulled up on the datalist?
An 02 Sensor Mystery
- Thread starter hubertron
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Was that FFD (Freeze Frame Data) when the DTC set or just what you pulled up on the datalist?
This link is the freeze frame data from when the condition was triggered:
http://cashier-crocodile-74255.bitballoon.com/
These are speculative thoughts:
I notice that the freeze frame data shows a single incidence of a misfire on #2 cylinder, which is in bank 2. I think I would dig into that further. Perhaps there is a slightly clogged fuel injector, or a marginal coil. If #2 is firing poorly, it could cause erratic lambda readings on that bank, and could cause occasional out of spec readings from the downstream O2 sensor.
This much I do know:
The downstream O2 sensor is there to ensure that the cat is doing its job. The cat can only do its job if it gets a stable stream of stoichiometricly burned gases as input. That can only happen if all 4 cylinders in a bank are operating properly and similarly, so that the upstream O2 sensor can tune the mixture properly. An out of spec or clogged fuel injector will throw a monkey wrench into the whole system, as will a marginal ignition pulse.
Another way of saying it is that the downstream O2 sensor is really the final check on the actual tailpipe emissions. As [MENTION=100496]blackworks[/MENTION] pointed out earlier, a downstream O2 sensor "failure" is often just saying that something upstream is out of whack; not enough to throw a code directly, but enough to cause an emissions failure at that instant. If you had a tail pipe sniffer measuring your emissions at the exact time of the code failure, my guess is the sniffer would have also shown emissions to be momentarily out of spec.
I notice that the freeze frame data shows a single incidence of a misfire on #2 cylinder, which is in bank 2. I think I would dig into that further. Perhaps there is a slightly clogged fuel injector, or a marginal coil. If #2 is firing poorly, it could cause erratic lambda readings on that bank, and could cause occasional out of spec readings from the downstream O2 sensor.
This much I do know:
The downstream O2 sensor is there to ensure that the cat is doing its job. The cat can only do its job if it gets a stable stream of stoichiometricly burned gases as input. That can only happen if all 4 cylinders in a bank are operating properly and similarly, so that the upstream O2 sensor can tune the mixture properly. An out of spec or clogged fuel injector will throw a monkey wrench into the whole system, as will a marginal ignition pulse.
Another way of saying it is that the downstream O2 sensor is really the final check on the actual tailpipe emissions. As [MENTION=100496]blackworks[/MENTION] pointed out earlier, a downstream O2 sensor "failure" is often just saying that something upstream is out of whack; not enough to throw a code directly, but enough to cause an emissions failure at that instant. If you had a tail pipe sniffer measuring your emissions at the exact time of the code failure, my guess is the sniffer would have also shown emissions to be momentarily out of spec.
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