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      04-19-2016, 11:02 AM   #1
TWiTCHY
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274B Code: O2 Sensor, or Cyl 8 Misfire?

Search is bringing up two different possible descriptors for the 00274B that Carly is showing (see pic). Does anyone know which is correct? Carly doesn't have the best or most accurate descriptions, I've heard, so I want to make sure I'm diagnosing the issue correctly.

This also popped up maybe 100 miles after an oil change.
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      04-19-2016, 12:24 PM   #2
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That is a code I have experience with, except in my case it was cylinder #6. What it boiled down to was a bad pre-cat oxygen sensor. Replaced and problem gone (before I knew better and swapped the coils around and then replace that coil with a new one, but no change). Not sure why it only specifies one cylinder when that whole bank should be affected but it's a bad o2 sensor.
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      04-19-2016, 12:30 PM   #3
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Quote:
Originally Posted by VictorH
That is a code I have experience with, except in my case it was cylinder #6. What it boiled down to was a bad pre-cat oxygen sensor. Replaced and problem gone (before I knew better and swapped the coils around and then replace that coil with a new one, but no change). Not sure why it only specifies one cylinder when that whole bank should be affected but it's a bad o2 sensor.
Thank you! So...I did take my car onto some farmland where my O2 wiring could have gotten caught on some tall grass. I'll check it out thanks again!
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      04-19-2016, 12:41 PM   #4
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My car threw code 274A the other day, which is a code related to the other pre-cat O2 sensor...I'm replacing it tonight so I hope it solves the issue
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      04-19-2016, 06:12 PM   #5
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Quote:
Originally Posted by TWiTCHY View Post
Thank you! So...I did take my car onto some farmland where my O2 wiring could have gotten caught on some tall grass. I'll check it out thanks again!
Sensor wiring is nicely tucked away, tall grass won't do anything. The pre-cat O2 sensors are running about $115 on Amazon right now (they vary from $105 to $180 at different times for the same thing, not sure why)
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      04-19-2016, 06:13 PM   #6
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Quote:
Originally Posted by VictorH
Quote:
Originally Posted by TWiTCHY View Post
Thank you! So...I did take my car onto some farmland where my O2 wiring could have gotten caught on some tall grass. I'll check it out thanks again!
Sensor wiring is nicely tucked away, tall grass won't do anything. The pre-cat O2 sensors are running about $115 on Amazon right now (they vary from $105 to $180 at different times for the same thing, not sure why)
Yeah I realized that after taking a peek underneath. I cleared the code and it hasn't popped back up yet. Will keep an eye on it before I decide to pick up a new sensor.
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      04-19-2016, 07:03 PM   #7
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Originally Posted by TWiTCHY View Post
Yeah I realized that after taking a peek underneath. I cleared the code and it hasn't popped back up yet. Will keep an eye on it before I decide to pick up a new sensor.
The sensors stop reading correctly well before they throw a code, so if you care about power and performance you may want to replace it sooner.

Mine were toast at 40k miles, 15k of that being catless.
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      04-19-2016, 08:37 PM   #8
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just replaced both of mine tonight. Took the car for a drive after and immediately could feel the car running better. Also sounded better.
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      04-20-2016, 01:54 AM   #9
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The sensors stop reading correctly well before they throw a code, so if you care about power and performance you may want to replace it sooner.

Mine were toast at 40k miles, 15k of that being catless.
Since it has thrown a code, does that mean they're done? I cleared it and it still has not come back after a 40 mile drive. How else can I diagnose a dead pre-cat O2 sensor? Car seems fine to me and no CEL.
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      04-20-2016, 11:31 AM   #10
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If it's bad it will come back. In my case I could run a day sometimes a day and a half and the code would come back. You can always hope but usually something's amiss when it starts throwing codes.
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      04-20-2016, 11:39 AM   #11
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Originally Posted by TWiTCHY View Post
Since it has thrown a code, does that mean they're done? I cleared it and it still has not come back after a 40 mile drive. How else can I diagnose a dead pre-cat O2 sensor? Car seems fine to me and no CEL.
no, but they're probably on their way out.

I had hesitation at high rpms with my blower and new primary o2's sorted it out.

They are sensitive wideband sensors so if the readings are off, it will directly impact performance
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