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Bank 2 is the drivers side of the engine on your 1999 Mercury Marquis Sensor 1 is before the catalytic converter ( upstream ) Sensor 2 is after the catalytic converter ( downstream )
On a 1998 Mercury Grand Marquis : Bank 2 is the drivers side of the engine Sensor 1 would be in the exhaust close to the engine before the exhaust enters the catalytic converter ( upstream sensor )
On a 1996 Mercury Grand Marquis , 4.6 liter V8 engine : Bank 1 is the passenger side of the engine Sensor 2 would be AFTER the exhaust has passed through the catalytic converter
On a 1998 Mercury Grand Marquis : Bank 1 is the passenger side of the engine Sensor 2 is AFTER the exhaust has passed through the catalytic converter
Bank 2 is the drivers side of your engine , Sensor 1 is in the exhaust before the catalytic converter ( upstream )
On a 1997 Mercury Grand Marquis : Bank 2 is the drivers side of the engine and ------------------------------------------------------------------------------------------ Sensor 1 would be close to the engine before the exhaust enters the catalytic converter Sensor 2 would be AFTER the exhaust has passed through the catalytic converter ( also called a catalyst monitor )
firewall 4 - 8 3 - 7 2 - 6 1 - 5 front of Mercury Grand Marquis
Bank 2 is the drivers side of the engine in a 2000 Mercury Grand Marquis
Bank 1 is the passenger side of the engine in a Mercury Grand Marquis Sensor 1 would be in the exhaust close to the engine before the exhaust enters the catalytic converter ( upstream sensor )
The oxygen sensor for bank 1 sensor 1 for a 2000 mercury mountaineer is on the cylinder #1 side.
P1131 = Insufficient switching O2 Bank 1 Sensor 1 Sensor/lean. Could be a B1 S1 O2 sensor going bad.
Bank 2 is the drivers side of the engine in your Mercury Mountaineer Sensor 2 is in the exhaust after the catalytic converter