02 sensors on a 2004 Mercury Grand Marquis
How many are there? 2 or 4? The dealership is trying to tell me there's only 3.
Doesn't make any sense to me.
The dealer is correct. There's 3. One is the upstream oxygen sensor and the other two are the downstream oxygen sensors. You have 2 catalytic converters. That's why there's 2 downstream oxygen sensors. HTH. -Jim
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