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How to Replace the Oxygen Sensor on a 1999 Saturn SL

The 1999 Saturn SL features a four-cylinder, 1.9-liter engine with two oxygen sensors that monitor the exhaust emissions. One is located directly into the manifold and can be accessed and replaced from the engine compartment. The other is located just behind the catalytic converter in the converter/front flex-pipe assembly. Because of the easier access to the "upstream" sensor (in the manifold), the sensor is actually easier to replace than the "downstream" sensor (near the converter), unlike the case with many other vehicles, which require you to get under the vehicle to replace any oxygen sensor.

Instructions

Downstream Sensor

1

Place a wheel chock behind one of the rear tires and then apply the parking brake to the Saturn SL.

2

Lift the drivers-side front quarter of the vehicle with a jack high enough to place a jack stand under the front frame rail (place it up in front of the converter to keep it out of the way of the work space). Repeat the procedure for the passenger-side front quarter to elevate the front axle.

3

Put on safety glasses and crawl under the front-center of the Saturn to the location of the steering rack just above the catalytic converter shell. The downstream sensor wire will be visible. The wire runs along the drivers-side edge of the converters heat shield and its plug connection is fastened up near the steering rack. Reach up to lift the wire harness plug clip lock while pulling the sensor wire mating plug free.

4

Snip the zip tie retainers of the wire down the length of the sensor wire. Repositioning from under the front-center over to the drivers side may help you reach the lower downstream zip ties to the sensor location.

5

Slide the heat-resistant cover off the oxygen sensor wire.

6

Align the sensor wire into the slot on the side of the oxygen sensor socket. Place the socket firmly onto the oxygen sensor. The small heat shield for the sensor makes it a tight fit.

7

Attach the ratchet to the socket and turn the sensor counterclockwise to remove it. It may be stubborn at first, but some leverage and ingenuity will pay off.

8

Hand-thread the new sensor into the oxygen sensor port. Tighten the sensor snugly with the ratchet and socket, again aligning the wire into the slot of the socket. Do not over-tighten or the threads of the sensor may strip.

9

Slide the original heat-resistant wire cover over the plug connection of the new sensor and feed it down to the sensor.

10

Plug the sensor back into the wire harness mating plug.

11

Zip-tie the wire to the heat shield, so it does not droop, before lowering the Saturn back to the ground.

Upstream Sensor

12

Open the hood and locate the upstream sensor. Its clearly visible in the front-center of the engine placed at the top of the manifold.

13

Disconnect the sensor harness plug from the wire harness mating plug located (and affixed) to the fan shroud. Lift the lock on the wire harness side of the plug and pull the socket wire plug away.

14

Place the socket onto the sensor, aligning the single wire into the slot of the socket.

15

Place the ratchet on the socket and turn counterclockwise to remove.

16

Place the new sensor into the sensor port, hand-tighten and the snugly tighten with the ratchet and socket before plugging the sensor into the wire harness mating plug. Close the hood.

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