Repair And Fix it

Oxygen sensors, commonly called O2 sensors, are a vital component in maximizing fuel efficiency in vehicles.

Name

An oxygen molecule consists of two atoms of oxygen bound together. Thus, O2 ers to the chemical formula for pure oxygen.

Task

O2 sensors monitor how much unburned oxygen is present in the exhaust from an automobile engine. The amount of oxygen indicates how efficiently the engine is burning fuel.

Effect

The cars computer uses readings from the oxygen sensor to adjust the mixture of air and fuel in the engines combustion chambers for maximum efficiency.

Location

There is an O2 sensor inside the exhaust manifold. Vehicles produced after 1995 also have a "downstream" sensor to measure the exhaust as it leaves the catalytic converter, to ensure that the converter is working properly, too.

Malfunction

Symptoms of a malfunctioning O2 sensor include declining gas mileage, rough idling and engine surges or hesitation. A vehicles "check engine" light will often come one.

The Chevy Tahoe was introduced in 1995, and it is a relative to the Yukon--the GMC version of the SUV. The Tahoe basically replaced the full-sized Chevy Blazer. Available since 1996 with V8 engines, the Tahoe features four O2 sensors (also known as oxygen sensors). There are two of these sensors located in front of the catalytic converter, and they are designed to monitor the fuel and air ratio mixture in the exhaust. Two more sensors are located near each converter, and serve to monitor their efficiency. One or more of these sensors can become defective and will need replacement.

Locating the Faulty Sensor

When an oxygen sensor fails, the "Service Engine Soon" light will illuminate on the dash. Take your Tahoe to an auto parts store to get the on-board computer scanned. Auto parts stores will perform this service for free, and they can help you determine which sensor(s) have failed. Since there are four sensors on most Tahoes, the scanner will be able to detect which one by reading the "check engine" codes: Bank 1, sensor 1 is the upstream sensor on the cylinder 1 side of the exhaust system; bank 1, sensor 2 is the downstream sensor on the cylinder 1 side; bank 2 sensor 1 is the upstream sensor on the opposite side of cylinder 1; and bank 2, sensor 2 is the downstream sensor on the same side.

Purchase direct-fit sensor(s). Direct-fit sensors integrate the plug-in outlet, therefore no rewiring is required. These sensors cost slightly more than universal sensors. Also, universal sensors require eliminating the male and female plug counterparts from the wire harness. Direct-fit sensors, however, do not require any wire splicing--they simply plug in to the existing wire harness connection.

Replacing the Sensor

Warm the engine up for a couple of minutes before you attempt to replace the sensor. This will expand the metal and make removing the sensor much easier. While the engine is running, spray a large amount of lubricant along the threaded joint of the faulty sensor(s) and allow it to soak in.

Disconnect the wire harness outlet from the sensor. The wire from the sensor runs about seven to eight inches from the sensor, and it is retained by a plastic clip, to prevent it from contacting the hot exhaust system.

Use a 22-mm combination hand wrench or an oxygen sensor socket and ratchet to remove the sensor. If using a wrench, insert the disconnect sensor wire through the box-end side of the combination wrench. If using an O2 sensor socket, insert the wire into the slot on the side of the socket. Turn the sensor counter-clockwise until it is loose. The sensors only have four to five threads, so it wont take much to loosen them enough to be removed by hand.

Apply a very light coat of anti-seize compound to the threaded section of the new sensor. Most direct-fit quality replacement sensors may already have a light coat on the threads. Be sure, if you have to add some on, that you do not get any on the thimble-shaped sensor--only a very light coat on the threads.

Thread the sensor into the port by hand at first, so that you dont cross-thread it. Tighten the sensor snugly with the wrench or socket and ratchet, but be careful not to over-tighten it. Since it only has four to five threads, sensors are very easily stripped out by over-tightening.

Plug the wire harness connection back together and re-secure the wire to the plastic retaining clip.

Resetting the Check Engine Light

Bring the Tahoe back to the parts store that sold you the O2 sensor(s) and scanned the trouble code for you. They will usually offer to reset the "Service Engine Soon" light for you. However, once the sensor(s) have been replaced, the computer will detect the new component and begin running through an inspection and maintenance (IM) self-diagnostic mode. This may take a few driving cycles to perform, as the engine needs to heat up and cool down repeatedly. Once the IM monitors have completed the self-diagnostic and detected that the new replacement sensor is performing its intended task, the on-board computer will turn off the "Service Engine Soon" light.

The oxygen sensors in your car perform several duties. Their primary function is to monitor and adjust your vehicles fuel mixture so that it gets the best possible fuel mileage while emitting the least amount of toxic emissions. Most vehicles have several oxygen sensors installed throughout the fuel system and engine, so the term "bank one" or "bank two" is used to identify the location of the sensor.

Age

No car part is built to last forever, and that is true for oxygen sensors as well. Over time, normal wear and tear can cause your oxygen sensor to fail. Common causes include the gases from engine emissions and buildup of naturally occurring engine deposits.

Chemicals

Oxygen sensors can be damaged by bad gas, leaded gas, internal coolant leaks, burnt oil and even products that have been applied to other parts of the engine to fix problems, such as gasket sealers. Oxygen sensors are really only meant to be exposed to good quality fuel, so other additives or chemicals can cause them to stop functioning properly.

Heating Circuit

Most modern O2 sensors have an electrical heating circuit built into the sensor. If the electrical heating circuit malfunctions or fails, it is not uncommon for the entire oxygen sensor to fail.

Replacing the oxygen (O2) sensor in your 2000 Honda Civic can improve the vehicles idle, fuel economy and engine performance. The O2 sensor reads the percentage of oxygen in the exhaust gases as they exit the engine, then converts that information to milliamps--these are used by the engine management computer to adjust the air/fuel mix going into the engine. If a sensor fails, the engine will run very rough and even stall during driving.

Instructions

1

Raise the front of the car with a jack, then support the car on a set of jack stands. Slide under the car, just behind the front wheels, and locate the O2 sensor on the catalytic converter.

2

Disconnect the electrical connector on the O2 sensor pigtail from the connector on the main wiring harness by releasing the locking tab and separating the two halves. Place an O2 sensor socket on the sensor, then turn it counterclockwise with a ratchet, removing the sensor from the catalytic converter.

3

Insert a new O2 sensor into the threaded hole in the catalytic converter and turn it clockwise, using an O2 sensor socket and ratchet to tighten it. Connect the wiring harness connector on the car to the pigtail connector on the O2 sensor, pushing them together until the locking tab snaps in place.

4

Slide out from under the car, raise the car off the jack stands with a jack, then remove the stands from under the car. Lower the jack, setting the car on the ground, then remove the jack from under the car.