Thread: Bad cat?
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Old 01-04-2009, 08:38 PM
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cruzalekz
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Default o2 sensor and cat reply

this is a problem with the scanner, parts store scanner is probably a cheap one.
expensive scanners would say "rear o2 sensor below threshold"
if you get that code, this is where a tech comes in and does a o2 sensor swing test with a scanner, You have two o2 sensors, one on the pre cat side and one is the post cat. Normally, pre cat o2 sends a faster signal than the post cat.
In your case, your pre cat and post cat o2 sensors were swinging the same rate and because im a technician, i interpret this as a bad/degraded catalytic converter and not a bad rear o2 sensor.
time to get a new cat..

by any chance is there another code besides the rear o2? sample a misfire code perhaps or a lean code

just trying to figure out if your cat went bad as a result of another engine problem.
good luck

Last edited by cruzalekz; 01-04-2009 at 08:41 PM.