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Old 11-14-2012, 10:47 AM
foaxaca foaxaca is offline
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Location: Rancho Cucamonga, CA
Join Date: May 2009
Posts: 21
Mein Auto: 1996 328is
By codes do you mean post-cat O2 sensors showing an issue? I don't think there is any other reading that is related to the function of the cats. That's what those O2 sensors are for. It may mean changing those also. They don't affect the functioning of the cats. I have looked into the possibility of having to replace the cats and there are some cheaper alternatives. One thing to make sure of (I'm sure you've heard this already) is to make sure the exhaust is up to regular operating temp for the test. Run it on the freeway for 20 minutes and keep it running right up to the test. The tester may even let you keep it running onto the dyno. I've even read to wrap the cats temporarily in insulating heat shield material to get the temp even higher to increase their efficiency. Only about 179k on the odometer of my daughter's car so determined to get it to pass. Also heard about a product called CRC "Guaranteed to Pass" which is another fuel additive that seems to get good reviews from others facing the same issues. Oil change with 20-50W to reduce splash on cylinder walls is another recommendation I've heard to keep HC numbers down.
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