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Automotive/2003 BMW 540i . . .need to know which o2 sensor is bank 1, sensor 1

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Expert: Sean Halliday - 9/16/2007


Question
Help. . .I am trying to replace a bad o2 sensor.  The OBD II said the o2 sensor at bank 1, sensor 1 is bad, but I don't know which side that is.  I know is it toward the front, but other than that, I don't know.  I would love to know where I can get a hold of a diagram for this.  Thank you for any possible assistance!

Mary

Answer
Sensor 1 is the sensor in front of the catalytic convertor.If  your car is the V8,its the passenger side front but i would change both front 02 sensors at the same time.Sensor 1 is always the upstream sensor and sensor 2 the down stream sensor,after the cat,convertor.

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Sean Halliday

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general auto repair,japanese,bmw,mercedes,mini cooper 1960/2009,general british cars,ford.I DO NOT work on automatic transmissions.Manual transissions i install clutches only.Many people ask me to diagnose noises from their cars,unfortunately i cannot do this unless i hear it.As you appreciate,vehicles can and will make a variety of noises.I DONT UPGRADE or fit aftermarket performace kits,parts,chips,only replacement parts.

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40 years experience on all general auto repair.

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