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Pelican Technical Article:

Oxygen Sensor Replacement

Jared Fenton

Time:

1 hour1 hr

Tab:

$150 to $300

Talent:

****

Tools:

10mm socket, oxygen sensor socket, floor jack, jack stands, wheel chocks, safety glasses, torque wrench

Applicable Models:

Jetta MkIV 2.0L (1998-05)

Parts Required:

Oxygen sensor

Hot Tip:

Replace the sensors with the engine cold

Performance Gain:

Better running engine

Complementary Modification:

Change spark plugs

The oxygen sensors are a very important part of the fuel injection system. They measure the oxygen content of the exhaust and send signals to the fuel injection computer, which in turn, will adjust the fuel/air mixture. When the sensors start to fail, you'll notice a loss of power, fuel economy and possibly a rich mixture smell coming from the tail pipe. This is because the engine goes into a default rich mode when it detects the oxygen sensor performance is below the regular limit. This will usually trigger a Check Engine Light (CEL) indicating that the sensor is failing. You can monitor the sensor function using the factory VAG-COM diagnostic computer or an aftermarket OBD-2 reader.

Many times, the CEL will note only one particular sensor that has gone bad. You can replace only that sensor. I usually recommend replacing all of the sensors at the same time, especially if the vehicle has 80-100,000 miles on it. It has been my experience that replacing only one leads to the others failing in a short amount of time.

To gain access to the post catalytic converter sensor, you'll need to jack up your Jetta and place it on jack stands at all four corners. See our article on Jacking up Your Mk4 Jetta for more information.

Shown here is an oxygen sensor socket.
Figure 1

Shown here is an oxygen sensor socket. The slit (green arrow) in the socket allows you to slip it over the wiring harness and down on to the oxygen sensor. The pre catalytic converter sensor is located directly behind the intake manifold in the engine bay.

Remove the pre catalytic converter sensor from the exhaust using the oxygen sensor socket.
Figure 2

Remove the pre catalytic converter sensor from the exhaust using the oxygen sensor socket. When fitting the new sensor, take care not to get any of the factory applied anti-seize compound on the tip of the sensor. Tighten the sensor until you feel the crush washer seat on the exhaust.

From underneath the car, pull the wiring harnesses for both the front and rear sensors out of the body clips (green arrows) securing them in place.
Figure 3

From underneath the car, pull the wiring harnesses for both the front and rear sensors out of the body clips (green arrows) securing them in place. Now loosen and remove the two 10mm nuts (purple arrows) securing the protective cover to the underside of the chassis.

Under the protective cover are the electrical connectors for the oxygen sensors.
Figure 4

Under the protective cover are the electrical connectors for the oxygen sensors. Pull the connectors out of the cover and then press the tabs on each to separate them. Note that they are color coded to prevent you from mixing up the pre and post catalytic converter sensors.

Now remove the post catalytic converter sensor from the exhaust using the oxygen sensor socket.
Figure 5

Now remove the post catalytic converter sensor from the exhaust using the oxygen sensor socket. When fitting the new sensor, take care not to get any of the factory applied anti-seize compound on the tip of the sensor. Tighten the sensor until you feel the crush washer seat on the exhaust.

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Page last updated: Sat 12/3/2016 03:10:20 AM