where is the 3rd O2 Sensor located?
The Downstream H02S or Catalyst Efficiency Monitor is mounted in the exhaust directly after the Catalytic Converter. There will be a sensor in each exhaust pipe right after the exhaust manifold on both sides of the engine - there will be "Y" where the two pipes come together into the Cat - the sensor is right after the Cat (it usually has a blue wire shield). Why? Did you get a code for it? People don't generally change them for maintenance.
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