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Old 02-28-2014, 03:58 PM   #1
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Code 21 and no O2 sensor

PO had a header put on, leaving the exhaust with no O2 sensor. Code 21 came up. Not sure how to fix?

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Old 02-28-2014, 04:15 PM   #2
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buy a O2 sensor and plug it in.

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Old 03-01-2014, 10:06 AM   #3
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There is no place to install the O2 into the header. Wouldn't just plugging it in and have it hang out cause other problems?
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Old 03-01-2014, 03:17 PM   #4
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They make a replacement bung, that you can weld into the header if you want to replace the O2 sensor. You have to buy that part, because O2 sensors have their own thread pattern. A regular nut or threaded bushing won't work.
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Old 03-01-2014, 03:35 PM   #5
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You can buy an exhaust downpipe from autozone that has the bung already installed. You'll have to take off the downpipe anyway to drill and add a new bung, but it's easier to remove and replace entirely if you don't have access to a welder. The downpipe disconnects from the exhaust manifold, and then from the Cat. I have replaced 2 downpipes so far and it's cake as long as you PB Blast the bolts ahead of time.
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Old 03-01-2014, 11:15 PM   #6
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Thx for the info on options. I have a welder, not wired for it, but soon. Also need to replace the downpipe, current one is dented, welder also needed. Sounds like welder is going to get up and running!
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Old 03-02-2014, 03:04 PM   #7
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Depending on what header you have on it, you can get a down pipe for a TJ 4.0, and it will go around the front of the oil pan instead of crossing over behind it like a YJ does.

Its a thought. It will protect your pipe better (less likely to get dented) but it does make it a PITA if you have to remove the starter.
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Old 03-02-2014, 10:44 PM   #8
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probably will stick with stock route, no idea what header it is. PO used the rig for weed spraying on a ranch. The underside needs attention from bumper to bumper. Thx for all the info so far fellas.

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