Diagnosing Cat/o2 sensor CEL
05-05-2016, 11:59 AM
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Diagnosing Cat/o2 sensor CEL
I have an 08 at 133k miles with a slightly mystifying CEL. It's bone stock with the exception of a catback exhaust. The light will stay on for 500 miles or so, and then turn off for 500 miles. Every time it comes back on, it is with two codes. I have seen codes for all 4 sensors being bad, and both cats, but only two come on at a time in any random combination.
Due to the random nature of the light, I thought it may have been an upstream vacuum leak so I replaced all the intake manifold and throttle body gaskets, as well as the injector o rings. The car did have an aem short ram on it when I bought it, so I'm thinking the MAF sensors may be dirty. I've since gone back to stock airbox with brand new filters. Also the throttle bodies were all gunked up, but I read horror stories of people shorting them out while cleaning so I left them alone. I did clean the rest of the intake tract though. It drives totally fine with the exception of a very slight random hesitation at low rpm's, what I perceive as a very slight rough idle condition, and perhaps a slightly richer than normal smell from the exhaust. Any ideas welcome, thanks.
Due to the random nature of the light, I thought it may have been an upstream vacuum leak so I replaced all the intake manifold and throttle body gaskets, as well as the injector o rings. The car did have an aem short ram on it when I bought it, so I'm thinking the MAF sensors may be dirty. I've since gone back to stock airbox with brand new filters. Also the throttle bodies were all gunked up, but I read horror stories of people shorting them out while cleaning so I left them alone. I did clean the rest of the intake tract though. It drives totally fine with the exception of a very slight random hesitation at low rpm's, what I perceive as a very slight rough idle condition, and perhaps a slightly richer than normal smell from the exhaust. Any ideas welcome, thanks.
Last edited by Bonfire; 05-05-2016 at 12:32 PM.
05-05-2016, 12:24 PM
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Yeah I replaced the plugs with oem iridium type. I don't think the cats are clogged, the car pulls very strong. I guess anything is possible though. Really trying to exhaust all possibilities before I go through the hassle of buying low mileage cats and o2 sensors. Such a pain to install haha. I also really doubt ALL of my sensors and cats went bad at the same time, so thats what leads me to believe there is some other root cause for all of this.
Last edited by Bonfire; 05-05-2016 at 12:49 PM.
05-05-2016, 01:01 PM
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ECU has been reset multiple times. No change. My next round of work was going to be clean the MAFs and throttle bodies, then do the throttle relearn if that doesnt fix it. I am not familiar with the idle air relearn.
05-05-2016, 01:08 PM
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There is a how to out there somewhere. Drinking a beer now so not going to cut into that time to look for it
DO NOT TOUCH THE BUTTERFLIES IN THE THROTTLE BODY. Just spray them off, make sure you remove negative battery terminal before you remove them
DO NOT TOUCH THE BUTTERFLIES IN THE THROTTLE BODY. Just spray them off, make sure you remove negative battery terminal before you remove them
Last edited by travlee; 05-05-2016 at 01:09 PM.
05-05-2016, 01:14 PM
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edit: yeah i read about that guy that fried his ecu cleaning the throttles. will be careful.
Last edited by Bonfire; 05-05-2016 at 01:16 PM.
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