Repair 7

When an oxygen sensor (also called an O2 sensor) is malfunctioning on a truck, the engine control unit isnt getting the proper information it needs to run the engine; as a result, the car may run poorly. The fix is to replace the sensor, and its a lot easier to do than one might think. This job should take about 30 minutes to do, depending on the year, make and number of O2 sensors on the truck.

Instructions

1

Lift up the vehicle using the jack and place it on jack stands. Make sure the vehicle is secure before you crawl underneath it.

2

Crawl underneath the truck and find the oxygen sensors. These are little metal tubes that stick out perpendicular to the exhaust tubing, typically near the catalytic converters. They also have two wires coming out of the ends, making it the only thing with wiring leading into the exhaust. Unplug the wiring to the O2 sensor using your hands.

3

Place the O2 sensor socket on the 3/8-inch ratchet and put the socket on the sensor so that the wiring is running out of the slot in the socket body. Unbolt the sensor and place it to the side. Repeat this process for any other O2 sensors that you want to remove.

Since the introduction of the Onboard Diagnostics II (OBD II) system in 1995, two oxygen sensors -- front and rear -- monitor engine performance and emissions in all American-sold vehicles. These small, but vitally important components communicate with the engine control unit to maximize performance and minimize emissions, and should be replaced or fixed immediately if found to be malfunctioning.

Front Oxygen Sensor Function

The front -- or upstream -- oxygen sensor, so named for its position in front or upstream of the catalytic converter in the exhaust manifold, measures the amount of unburned oxygen present in the exhaust that exits the engines combustion chamber by producing and reporting a voltage level to the ECM. This indicates the air to fuel ratio that the engine is receiving and whether or not the ECM needs to alter that mixture in order to reach the proper 14.7:1 ratio.

Rear Oxygen Sensor Function

The rear oxygen sensor is located downstream of the catalytic converter, and has a more basic function: it monitors the effectiveness of the catalytic converter. Tasked with removing many of the harmful toxins from engine exhaust, the catalytic converter is an important part of the exhaust process. The ECU compares data compiled from the rear oxygen sensor with that of the front oxygen sensor to ensure that the catalytic converter is doing its job. A non-functioning rear oxygen sensor wont affect performance, but it will likely trip a dashboard indicator.

Design

Although they have different purposes, front and rear oxygen sensors employ the same basic design to measure oxygen levels. Resembling spark plugs, these small devices produce a voltage between 0.2 and 0.9 volts, based on the amount of oxygen flowing past their bulb, and relay that information to the ECU. Most modern day oxygen sensors are electrically heated on start-up until they can maintain their own 600-degree operating temperature.

Oxygen sensors have been integrated on vehicles for more than 30 years. Located in the exhaust system, they monitor fuel-to-air ratio and catalyst efficiency. While working in a hostile environment, the sensors can eventually fail and require replacement. When this occurs, a diagnostic trouble code illuminates the check engine light to warn the driver of the component failure. Ignoring the light and not replacing the sensor can lead to further problems with the engine and emissions control system.

History

Volvo was the first auto manufacturer to feature the oxygen sensor in 1976. The sensors were specifically designed to lower emissions in the state of California to help prevent high levels of pollution. Saab soon followed suit. By 1980, almost every vehicle on the road employed one in or near the exhaust manifold. Soon, another sensor was installed into the exhaust system to monitor the efficiency of the catalytic converter. All vehicles now have at least two sensors, and some can have up to four.

Function

The upstream oxygen sensor monitors the fuel-to-air ratio for the combustible engine. A perfect mixture provides a smooth-running vehicle with lower exhaust emissions. The sensor transmits the information by radio signal to the computer of the vehicle. The computer reads the signal and makes required adjustments to the fuel-to-air mix. The downstream sensor simply monitors the catalyst efficiency and again transmits the information to the computer. When the upstream sensor fails to communicate correctly, the computer is unable to make the required adjustments and a rich or lean fuel to air mixture occurs. This causes unburned fuel to contaminate the inside of the catalytic converter.

Types

The older oxygen sensors featured a single wire to plug into the wire harness and communicate to the computer. The vehicle had to get up to operating temperature before the sensor was activated to transmit the data. This caused higher emissions to be exhausted from the engine until the sensor began to function. Newer sensors now have three to four wires. An internal heater inside the sensor heats it up more quickly to activate the function of the sensor more quickly, resulting in lower emissions.

Significance

The oxygen sensor is in place to monitor the emissions from the exhaust. Without the sensor in place or with a failed sensor, the computer cannot adjust the fuel-to-air ratio properly. This causes a rich (too much fuel) or lean (too much air) mixture. It can affect the operation of the engine and allow unburned fuel to emit down the exhaust system. When the catalyst cannot convert the unburned fuel, particles will build up on the special metals inside the catalyst. Eventually, the converter will break down inside and require replacement.

Location

As mentioned, many vehicles have multiple oxygen sensors integrated into the exhaust system. The upstream sensors are located before the catalytic converter, often near or on the manifold. Vehicles with dual manifolds will have a sensor for each. The downstream sensors are located after or in the catalytic converter. Vehicles featuring more than one converter will have one sensor for each one. Bank location of the sensors will help you determine its proper location. Bank 1 is located on the same side of the engine as the No. 1 cylinder. So a diagnostic trouble code that tells you Sensor 1 Bank 1 has failed indicates the upstream sensor on the same side as the No. 1 cylinder. Sensor 2 Bank 1 is the downstream sensor on the same side.

Oxygen sensors have two basic functions: upstream sensors close to the manifold meter the amount of oxygen and burned fuel mixture in the exhaust; downstream sensors located near the catalytic converter monitor the catalyst efficiency. If too much fuel or too much oxygen is read by the sensor, it transmits the information via radio signal to the PCM, which then makes adjustments in the engine to correct the problem. Oxygen sensors wear out after a while and need to be replaced during regular maintenance schedule intervals.

Finding the Right Sensor

The hardest part of replacing an oxygen sensor is locating the correct one. Vehicles nowadays have at least two, but some can have up to four sensors. When the sensor fails to transmit or a noticeable problem in the fuel mixture is detected, the PCM will trigger the "check engine" light to alert the car owner that there is a problem. All vehicles built after 1996 have universal PCM plug-in sources called "DLCs," or "data link connectors." A scan tool or code reader will allow you to find out the problem or narrow it down by plugging it in to the DLC and then reading the code. But what if it says something like, "circuit failure sensor 1 bank 2?" Banks and sensor numbers are used to help identify the location of them in the exhaust system. "Sensor 1" indicates a forward or upstream sensor towards the manifold; "banks" indicate the split in the exhaust system, such as a Y-pipe coming off the engine or a genuine dual exhaust system. Bank 1 is most often located on the same side of the vehicle--left or right--as the number one cylinder. So sensor 1 bank 2 would be located upstream near the manifold on the opposite side of the number one cylinder.

Access

Access to some of the sensors nowadays is somewhat challenging. Most vehicle manufacturers place the oxygen sensors in conspicuous places that can easily be accessed. Others may make you wonder what they were thinking when they designed the exhaust system. There are tools to help make it easier for you and a trick or two that might work. Once youve located the correct sensor or sensors, unplug the sensor from the wire harness.

Tools

Oxygen sensor wrenches or sockets are available in most parts stores nowadays. Although they make the job a whole lot easier, theyre not magic wands. Limited access is still going to challenge you, and corrosion on the old sensor and exhaust pipe may be another obstacle. Remove the sensor once youve gotten the tool onto it by turning the tool counterclockwise. A degree of force will be required, but if it doesnt feel like its going to budge, heating up the portion of the exhaust pipe that surrounds the threads of the oxygen sensor might help. This can be done with a portable propane torch. Dont heat the sensor as well. Youre goal is to expand the exhaust pipe and not the sensor. Being careful not to burn yourself, retry removing the sensor with the wrench or socket until youre successful. If you dont have a torch, try running the car long enough to heat the exhaust system up for a while and then liberally spray lubrication oil on the sensor.

Replacement Sensors

Replacement sensors range in price from $50 to $120 a piece. Bosch makes a decent direct-fit aftermarket sensor made specifically for most vehicles at an affordable price. The dealership will sell direct-fit original equipment sensors, but will be on the high end of the price range. You may discover in your hunt for the best price that a universal sensor is available for many cars. This means the sensor can be wired in and used in more than one application non-specifically. Although its cheaper and sounds like a good deal, keep in mind that in addition to removing and replacing the oxygen sensor, youre going to have to cut and splice wires--that most likely will not color-code the same way on both ends. For a few dollars more, your money will be well spent for a name-brand direct-fit oxygen sensor made specifically for your vehicle.

Automotive oxygen sensors, or 02 sensors, are little electronic devices that measure the amount of oxygen in a cars exhaust, helping to reduce pollution and increase fuel economy. Oxygen sensors were first implemented in 1976 when automaker Volvo engineered them into the exhaust system of a car called the 240.

Basic Function

O2 sensors are designed to help regulate emissions from the exhaust. They are often located in the exhaust manifold; their basic function is to monitor the amount of unburned oxygen that passes through a cars exhaust system. O2 sensors send messages to the automobiles computer telling it if the fuel mixture is burning too much or not enough oxygen.

Significance

In the early 1980s California required that all new cars sold in the state must have oxygen sensors. Several other states followed suit, and by the late 1990s O2 sensors are required equipment on all automobiles sold in the United States.

Design

O2 sensors are equipped with a zirconium ceramic bulb located within a vented cover that screws into the exhaust manifold. With a coated layer of porous platinum, the bulb also has two strips of platinum inside to act as electrodes.

How They Work

As hot gases pass through the cars exhaust system, they pass through the vented end of the oxygen sensor. The ceramic bulb on the O2 sensor gets exposed to the hot gas and experiences an increase in voltage output that represents the difference in oxygen levels between the exhaust and the outside air. A higher release of voltage indicates a great difference in these two factors. The automobiles computer reads this information and compensates for the lopsided ratio accordingly by leaning the fuel mixture with either the carburetor or throttle-body, depending on type of vehicle it is.

Warnings

O2 sensors, like all automobile components, wear out with age. Dirt, grease and grime are the most common factors that result in damaged or faulty oxygen sensors on automobiles. Driving with a faulty O2 sensor will cause increased fuel consumption as well as higher outputs of exhaust pollution than with a working O2 sensor.