praetorian300

Last night while driving the SES light randomly came on and i pulled the code 0409 when i got home. i checked on here and it says the code is for a malfunctioning oxygen sensor. after i reset the light i went and drove and the car as performing a whooooole lot better and when floored it would shift/acclerate a lot quicker. after i turned the car off again and started it back up, it was back to being its sluggish self. so im wondering if its the o2 sensor thats causing this or if it could maybe be a bad knock sensor or something like that which was reset when i cleared the MIL.... thanks

-doug

maximachad

It's definitely your knock sensor...that happened to me. Get it replaced, and your car should be back to normal. If the knock sensor is going bad and not telling the ECU to supply enough fuel, it can cause a knock which causes your ECU to retard engine timing. (This also happened to me). Since replacing the O2 sensor, no problems!
P.S. - You can do this yourself pretty easily, as I did. Most dealers charge around $180-$220 to replace it for you.
-Chad

praetorian300

so did you replace both the o2 and knock sensors, or just the knock sensor?

iwannabmw

iTrader: (3)

If the light comes back with just a 0409 code again, replace the 02 sensor. That can easily cause a loss of performance as well.

If you're not getting the knock sensor code when you read them, consider yourself lucky, as that definitely isn't the problem in your case then.

maximachad

Just the O2 sensor. Check after a couple of weeks to see if you're getting any codes. (Light doesn't have to be on) If you pull the knock sensor code after you replace the O2, then you'll need to replace that as well. Chances are you won't though. If you're only getting 0409, then the O2 sensor is your only problem right now.
-Chad

praetorian300

hey everyone, im so proud of myself because i replaced the o2 sensor that was bad today, even though it took 1.5 hours. well after i replaced it i cleared the ecu AND disconnected the battery to make sure all the codes were out. the power delivery seems to be a little smoother but my acceleration is still below what it should be and the time to kick down at WOT is still slow. what else could be causing the car to run slow? i know the knock sensor could be causing this but it isnt sending out a code....any ideas?

praetorian300

come on guys...suggestions?