How many oxygen sensors are there in a 1999 Toyota Sienna?

Answer 1

Answer

Three O2 Sensors. one in each exhaust manifold before the catalytic converters. then one after the cat.

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How to replace your downstream O2 sensor (the one after the cat, that's threaded into the exhaust pipe).

You need a Bosch 13353 Oxygen Sensor. This sensor IS an EXACT fit/replacement for your downstream sensor on a 1998 (1st gen) Toyota Sienna --- down to the wire holding clip.

The downstream sensor's connector on a 1998 (1st gen) Sienna is located under the front passenger seat.

*Remove the 4 - 14mm bolts holding down the seat.
*Prop the seat upward.
*Pull back on the carpeting slit to reveal the connector.
*Pinch the connector to remove the female end of it.
*Use a needle nose pliers to pull up and remove the rubber grommet from the floorboard, then push it down through the hole.
*Jack up the right front (behind right front wheel), then use a jack stand for safety.
Note: Make sure the exhaust pipe is well-warmed to the touch - for easier removal of the old sensor.
*Use a 22mm box wrench (counter-clockwise) to remove the old downstream sensor from the exhaust pipe.
*Install the new sensor (already contains anti-seize compound). Do not overtighten.
*Snake the wires/connector up through the floorboard.
*Use your needle nose pliers to pull the grommet up through the floorboard, then massage it into place with your fingers.
*Click the female connector into place.
*Re-install the seat.

Hey! You just saved big $bucks$ by doing this yourself.

Here is a link to a detailed post with pics of an O2 sensor replacement. The one replaced was between the engine and the firewall. Just cut and paste the link below...

"http://polifrogblog.blogspot.com/2009/11/sienna-o2-sensor-change.html"