How to Replace the O2 Sensor in a Mercury Grand Marquis
- 1). Park your Grand Marquis in a safe place with a level surface. Open the hood and disconnect the black, negative battery cable.
- 2). Raise the front of the car using a floor jack and safely support it on 2 jack stands.
- 3). Locate the downstream and upstream oxygen sensors. Follow the exhaust pipes connected to the exhaust manifolds on both sides of the engine. The upstream sensors are located closest to the exhaust manifolds, before the catalytic converter; the downstream sensors are located after the catalytic converter. The sensors are cylindrical in shape, about the size of a spark plug and threaded into the exhaust pipes.
- 4). Unplug the sensors electrical connectors by pressing the lock tab and pulling the sensor's plastic connector from the wiring harness.
- 5). Unscrew the sensors using a ratchet and oxygen sensor wrench. If the sensors are hard to remove, spray the threads with penetrating oil, following the product manufacturer's instructions; then remove the sensors from the vehicle.
- 6). Apply a light coat of high-temperature nickel anti-seize compound to the sensors' threads and start the sensors by hand to avoid damage to the threads. Tighten the sensors being careful not to over tighten.
- 7). Plug the sensors electrical connectors, lower the vehicle and connect the black, negative battery cable.
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