There are literally hundreds of things that can set off the SES light and you really have no way of knowing what it is. So DO NOT GUESS. Buy yourself an OBDII code reader (great tool to have anyway) or follow tnnntj's advice and have the code read somewhere. Once you know the code then post it up and we can try and trouble shoot it.
Went to autozone and the gentleman said they do not do the diagnostics anymore. (being sued or something). Then I asked how much the OBDII would cost me, he said "whats that"?
Went to kragen and bought one because I left Autozone frustrated. Code PO420 Is what the code reader gave me. "Catalyst System Efficiency Below Thresheshold (Bank 1).
Probably useless info but FWIW. I got a code once, took it to dealership (b4 I knew about Autozone) and they said it was the air-pump (into the exhaust) which supposedly keeps it cleaner somehow. The part was $240 so I just ignored it. I almost never get it anymore not even once since I started modding. Like I said probably useless
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'99 TA, M6, Flowmasters, BFG Comp T/A's ($210), Removed Ram Air Baffles and sealed the Air box($10), Polyurethane Tranny Mount($30,$30), Whisper LID($100) Holley Filter ($40), Smooth Bellows ($50), Cut Out($30,$80), TB Bypass ($10), Pro 5.0 Shifter ($195)
I would like to have no cats and do the longtubes. Here in California it would get me in trouble with the law. If there are any other ideas, please let me know
i just did a search on that error code (yes, im that bored ), and found out that a few people got that code because their 02 sensor was going bad (the one after the cat). i guess that could be the culprit. hope this helps, good luck!
i think if you pulled the sensor out you'd be able to tell that it didn't look right. I'm no expert by any means, but i'd just crawl under there and take a look.
Not only that, but o2 sensors are pretty cheap anyway, and fairly easy to replace.
Black 99 Trans Am A4
13.64 @ 103 (old time, before headers)
Slp induction package (Lid, Bellow, Ramair peice), Magnaflow catback, BMR Lower control arms, BMR Sub-frame connectors, Jet Hot long tubes, Mufflex y-pipe, 3.73's, tuning.
Yes, likely a bad O2 sensor. Check to make sure there are no exhaust leaks around the convertor area and there is no damage to the sensors or wire pigtails (e.g. burnt due to contact with exhaust, etc). Check to make sure the connectors are plugged in. You'll have one O2 forward of the cat and one behind. If all of the above checks out, I'd pick up a replacement O2 sensor and try that.
If you have access to Autotap or similar diagnostic software you may be able to run an O2 sensor test - I've never done it myself though.
*Note that I'm assuming you have the stock exhaust manifolds/cats. If you're using headers or have otherwise modified/relocated your cats, then I'd start there.
Picked up the sensor today, will hopefully be installing tomorrow. After install, do I erase the code with the OBDII and hope the light doesn't return? Or Do I undo the battery cable for fifteen minutes like I have read and hope the light doesn't come on?