I foolishly unplugged both O2 sensors at the same time..

Hi,

I foolishly unplugged both O2 sensors at the same time. Now I'm not sure which sensor cable plugs into which plug on the engine shelf. One is grey and the other is black.

Also, on the driver's side of the car 1999 996 are the sensors basically the same as they are on the passenger side as shown on the photo? Essentially, the sensor closest to the rear and just up from the other sensor is after the catalytic converter, while the sensor connected to the larger exhaust pipe is the one before the sensor? Thanks.

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This post was auto-generated based upon a question asked on our tech article page here: Porsche 911 Carrera Oxygen Sensor Replacement - 996 (1998-2005) - 997 (2005-2012) - Pelican Parts Technical Article

[Casey at Pelican Parts]

If I remember correctly, the sensors plugs are color coded, and the black is before the cat and the grey is for the one that screws in to the cat (aka post cat). You will know if they're plugged in incorrectly the car will run terribly.
The sensor closest to the rear and just up from the other sensor is after the catalytic converter, while the sensor connected to the larger exhaust pipe is the one before the cat. Yes you are correct!

- Casey

[monteolsen1]

I appreciate your reply. The plugs were reversed. It helped smooth out the missing a bit, but there is still a problem when I try to accelerate quickly. The engine starts missing, sometimes right after I push the gas pedal down and sometimes after the tach hits 4500 or 5000. But only when I put my foot into it with moderate pressure. If I push the gas pedal down gently, the engine doesn't miss and all is OK. I have already replaced the ignition coils in cylinders 1 and 2, and replaced all spark plugs. This problem arose after I changed the spark plugs and swapped one of the coils.

Thanks again for everything. I have your 101 Projects book and really find it useful.

Monte