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Discussion Starter #1
2000 SS 'Lude, AEM CAI & AEM pulleys, 14,500 miles...

Saturday I'm on the interstate, doing about 75, I see a "County Mounty" around a bend about 1/4 mile ahead. I hit the brake kinda hard and get it down to 65 really quick.

The "Check Engine" light comes on. Everything's running fine, can't feel or hear anything wrong.

I stop to buy gas about 4 miles down the road and when I opened the gas door, I find the cap sitting in the holder thingy. I had forgotten to replace it last time I filled up. (dumba$$)

The check engine light stays on after the fill-up. Car's still running fine. I get home and do a check on the pulleys and CAI to make sure nothing's loose. Everything's still fine.

I disconnected the battery cable for 30 seconds to reset the ECU. Re-connect, and the "Check Engine" light is no longer illuminated. Everything's running fine, still.

Q: Did the light come on because the gas cap was off, and I was near empty and slammed on my brakes, causing some kind of fuel pressure sensor to go off?

Q: Did unplugging the battery cable have anything to do with the light going off? I heard somewhere that you have to reset OBD II codes with a plug-in reader. The manual says that if it's a gas cap problem, the light will reset on its own.

Q: Could pulleys or a CAI cause the "check engine" light to come on? I wouldn't think so because the malfunctions that trip that particular light have to do with different sensors. Maybe some OTHER light would come on, but not "check engine".

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<font face="Verdana, Arial" size="2">Originally posted by Pete:
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Q: Did the light come on because the gas cap was off, and I was near empty and slammed on my brakes, causing some kind of fuel pressure sensor to go off?
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More than likely. You probably slapped the fuel around enough for it to think the cap was off (surprising it didn't do it earlier). This is a "feature" of OBD2.

<font face="Verdana, Arial" size="2">
Q: Did unplugging the battery cable have anything to do with the light going off? I heard somewhere that you have to reset OBD II codes with a plug-in reader. The manual says that if it's a gas cap problem, the light will reset on its own.
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I haven't checked it, but more than likely. All you needed to do was remove the CLOCK/RADIO fuse from the under-hood box. This removes the backup power from the ECU (as well as the radio, have your code handy). Could have just been a time-out or the ECU self-resetting.

<font face="Verdana, Arial" size="2">
Q: Could pulleys or a CAI cause the "check engine" light to come on? I wouldn't think so because the malfunctions that trip that particular light have to do with different sensors. Maybe some OTHER light would come on, but not "check engine".
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Shouldn't, though the ECU will correct eventually for the cams with ignition timing and fuel trim. You'll need to reset the ECU every few days or put a switch on the backup power line if you want to stop this. I'm not sure what pulley settings make what power, but I know the ECU is smart enough to adjust what it can to compensate for the altered emissions.

All ECU errors generate the Check Engine light. ATTS has it's own, the brake system has it's own, the ABS system... any engine or emissions related problem pops the Check Engine light.
 

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ok after reading this i just remembered that my girlfriend's jetta lost her gas cap and her check engine light came on. We found the gas cap and didn't think that was the reason the light came on. Does anyone know if resetting the ECU on her car is the same pull out the clock fuse thing?
 

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my check engine light came on for the same reason; although in my case the cap was on, just not quite tight enough. it takes quite a while for the ECU to clear that code if you don't reset it. i actually took it in to the dealer becaues it wasn't going away!

isn't that feature actually there to prevent the emissions emitted by gasoline when it evaporates into the open air? that's what i thought it was for... i'm sure you've all seen the ad that says a honda insight generates less emmisions on a 400 mile trip than are caused by spilling a few drops of gas when you fill it up.
 

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Discussion Starter #5
Thanks for the info.

Tony: I think most cars have the ECU connected to the same fuse as the clock/radio. They'll all reset if you disconnect the battery.
 
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