Post Cat O2 sensor out of range
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Post Cat O2 sensor out of range
I'm back again 
2 weeks ago when I was fighting the idling issue, I posted about the CEL coming on and the code was Post Cat O2 Sensor out of range. I had the guy at Advance Auto clear it. Here we are 2 weeks later, and the CEL comes on again. Back to Advance Auto, and it's the same code. Here's my question.....
The guy at Advance Auto says it could be the sensor or a bad catalytic converter. How do I know which one? Can I test the O2 sensor to see if it is bad? I don't want to just throw money at the problem (don't have much to throw these days).
Any advice?
2 weeks ago when I was fighting the idling issue, I posted about the CEL coming on and the code was Post Cat O2 Sensor out of range. I had the guy at Advance Auto clear it. Here we are 2 weeks later, and the CEL comes on again. Back to Advance Auto, and it's the same code. Here's my question.....The guy at Advance Auto says it could be the sensor or a bad catalytic converter. How do I know which one? Can I test the O2 sensor to see if it is bad? I don't want to just throw money at the problem (don't have much to throw these days).
Any advice?
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Sorry. 1996 Accord LX 2.2L
I believe the code is P0420 (maybe my car needs some weed) LOL
P0420
The scan tool indicates Diagnostic Trouble Code (DTC) P0420: Catalyst system efficiency below threshold.
I believe the code is P0420 (maybe my car needs some weed) LOL
P0420
The scan tool indicates Diagnostic Trouble Code (DTC) P0420: Catalyst system efficiency below threshold.
Last edited by ctconline; Aug 27, 2010 at 08:51 AM.
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From: Wisconsin
Don't know very specific, but I've heard that beginning in 1998 the ECU is very good at telling the difference between a bad cat (P0420) vs. a bad rear O2 sensor which would throw different codes.
I'm tempted to think that means earlier years like your 1996 were more likely to throw P0420 for a bad rear O2 sensor.
I'm tempted to think that means earlier years like your 1996 were more likely to throw P0420 for a bad rear O2 sensor.
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Jim..I am tempted to agree with you. I have had bad converters before and they usually make a lot of noise. I don't have a lot of noise. Of course, it could be that it is in the beginning stages of going bad. who knows...
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From: Wisconsin
Converters can go bad from the ceramic monolith breaking up & rattling. Or they can go bad by the catalyst getting chemically poisoned (lead or silica). So a silent converter doesn't REALLY prove that it's good.
Got a voltmeter? You want one with either a fast bar-graph (Fluke, etc) or an old analog meter with a needle. When the car's running, probe the O2 sensor signal wire while it's still connected. It should be about 1 to 1.5 volts but it should be fluttering up & down. Bad sensors usually are sluggish, so you want the fluctuations to be fast like 2 or 3 per second. If the voltage swings are slower than that, I'd probably change the sensor.
Got a voltmeter? You want one with either a fast bar-graph (Fluke, etc) or an old analog meter with a needle. When the car's running, probe the O2 sensor signal wire while it's still connected. It should be about 1 to 1.5 volts but it should be fluttering up & down. Bad sensors usually are sluggish, so you want the fluctuations to be fast like 2 or 3 per second. If the voltage swings are slower than that, I'd probably change the sensor.
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Here's an update. Instead of a voltmeter, I purchased an OBD-II to USB converter and PCMSCAN. It gives me a lot of information, but probably too much. I have cleared the MIL a couple of times, but it keeps coming back on (of course). The problem is that it never comes on when I'm testing it. I have recorded several logs, but neither of the O2 sensors are consistently between 1.0 and 1.5 volts. Thoughts?
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From: Wisconsin
What do the logs look like? What I described is kinda old-school method.
If they're centered in that area but go outside of those extremes that probably just means the measurement is more responsive than the method I described.
If they're centered in that area but go outside of those extremes that probably just means the measurement is more responsive than the method I described.
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Hey Jim.
It's kind of hard to describe. I just watched the log playback again. When I first started the car, the O2S11 was reading 0.425V and O2S12 was reading 1.150V. Then I start driving, and they are ALL over the place with O2S12 dipping all the way down to 0.015V and even 0.000V at times. This can't be normal, but again this didn't throw any code(s). I'm still not any closer to determining whether it's a bad sensor or a bad catalyst. Any ideas?
It's kind of hard to describe. I just watched the log playback again. When I first started the car, the O2S11 was reading 0.425V and O2S12 was reading 1.150V. Then I start driving, and they are ALL over the place with O2S12 dipping all the way down to 0.015V and even 0.000V at times. This can't be normal, but again this didn't throw any code(s). I'm still not any closer to determining whether it's a bad sensor or a bad catalyst. Any ideas?