Sonata GLS V6-2.7L (2002)
The picture explains the following terms:
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Engine BANK
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Up = Sensor 1 = Front = Closest to the exhaust manifold = Before the Catalyst
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Down = Sensor 2 = Rear = After the Catalyst
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Bank 1 is toward the Dash Panel
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Bank 2 is toward the Radiator
The following 02 Sensor EXAMPLES show how to interpret the terminology:
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B1/S1 = Bank 1/Sensor 1 = Dash Panel Side, BEFORE the catalyst
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B2/S2 = Bank 2/Sensor 2 = Radiator Side AFTER the catalyst