Glossary “O2 sensor” Definition:

A term used for oxygen sensor.

What is O2 sensor?

Every new car, and most cars produced after 1980, has at least one oxygen sensor. Its job is to help the engine keep a certain air-to-fuel ratio that balances power, fuel economy and emissions. The O2 sensor checks the amount of oxygen in the exhaust, compared to the amount in the air. It feeds that information to the engine computer, which then adjusts fuel and air intake.

Like most auto parts, the O2 sensor has a life span. Depending on the kind of sensor, it is typically from 30,000 miles to 100,000 miles. If your O2 sensor is failing, you may notice:

• Warning light on dashboard
• Sootier exhaust
• Lower gas mileage
• Hesitation when you step on the gas
• Stalling
• Rough idling

How to test a 5 wire o2 sensor?

A five-wire oxygen sensor is considered a wideband sensor. Traditional oxygen sensors have only one or three wires. The five-wire system allows the sensor to process more information, in turn creating a more accurate measurement for it to send to the engine computer. This allows the computer to more accurately process the exact amount of oxygen that is needed to maintain the air to fuel ratio. It’s important to learn the proper way to test a five-wire oxygen sensor, as the voltage is a bit different than traditional sensors.

• Drive the vehicle for ten minutes; this will allow the sensor to warm up to normal operating temperature. This is ideal for oxygen sensor testing and maintenance.
• Open the bonnet of the vehicle and locate the O2 sensor. The sensor is found mounted on the exhaust manifold. Refer to your repair manual, as location can vary slightly from manufacturer.
• Disconnect the wire harness from the oxygen sensor; depress the two side tabs, if present, and pull the harness straight out of the sensor.
• Turn the multimeter to the minivolts, or “MV,” setting. Connect the positive red multimeter lead to the signal wire on the O2 sensor. On a 5-wire oxygen sensor the signal wire is the middle wire. Connect the negative black lead to a grounded point.
• Start the engine and allow the sensor to work for one minute. Monitor the multimeter; you should notice the voltage jumping back and forth from high to low in the .1 to .9 minivolts. If the multimeter fails to register or does not jump; the sensor has no voltage and should be replaced.

How to Change an O2 Sensor?

The first indication that there is a problem with your vehicle’s oxygen sensor is when the “Check Engine” light comes on. A quick check with a handheld diagnostic scanner/reader will confirm that you need to change the oxygen sensor on your vehicle. Depending on the make and model of your vehicle, there will be between 2 and 4 O2 sensors located on your exhaust system-1 or 2 before the catalytic converter and possibly 1 or 2 after it. The diagnostic scanner/reader should tell you which bank of sensors has gone bad.

Steps:

1、Locate the oxygen sensor on your vehicle by looking for a part that looks like a spark plug that sticks out from the exhaust pipe. It will have an electrical connection attached to it.
2、Disconnect the electrical connection on the oxygen sensor. Use a flat tip screwdriver to push in the tabs and pull the connection apart.
3、Unscrew the oxygen sensor off the exhaust pipe using either an open-end wrench or a special socket made to remove it. The majority of oxygen sensors will take an SAE 7/8 inch wrench.
4、Compare your new oxygen sensor to the old one. If the new one did not come with an electrical connection, but just with the wires stubbed out, you need to do a little work.

• Cut off the old connector from the bad oxygen sensor, strip the wires and use butt connectors to attach it to the new oxygen sensor.
• Use heat sensitive shrink tape to seal the connections.
• Follow manufacturer’s instructions to know which wires to tie together.

5、Reverse the steps used in removing the oxygen sensor and install the new part. Screw it in place clockwise and snug it down with the socket or open-end wrench. Do not over tighten the sensor as you might strip the threads.
6、Plug the electrical connections back in.
7、Turn on the ignition key, but do not start your vehicle. Use the diagnostic scanner/reader to clear the code from the vehicle’s computer.
8、Start the car. You should notice an immediate improvement.

Where is the O2 Sensor Located?

An 02 sensor is a oxygen sensor and it measures the amount of oxygen in the exhaust. It is located in the exhaust manifold or in the downpipe before the catalaic converter. If the proper amount of oxygen isn’t in you exhaust, the 02 sensor makes the check engine light come on. And your car will not pass a smog test until that problem is fixed.

How To Replace O2 Sensor?

Is your Check Engine Light haunting you from the dash like a tiny, orange, burning ember? If it is, there’s a fairly good chance that a bad O2 sensor is causing the problem. These sensors go bad all the time. Some experts say that new fuels with higher ethanol content are causing parts of our cars, including the O2 sensors, to go bad prematurely. Whether this is the case or not, if your CEL (Check Engine Light) is on you won’t be on the road much longer thanks to most states’ inspection programs.
Of course before you go replacing an O2 sensor you’ll want to be sure that’s the problem. Even the parts are expensive, not to mention the labor if you’re paying a shop to do the work for you. A Check Engine Light can mean a lot of things, and even though the oxygen sensor is often the culprit, there are hundreds of other possibilities.

How To Fix An Car’s O2 Sensor?

If your car’s “Check Engine” light is glaring at you, it’s probably because the oxygen sensor is malfunctioning. That’s right, the oxygen sensor. It’s a little device that’s a mystery for most drivers but its misbehavior is the problem that most commonly triggers a Check Engine light, according to which sells an automotive diagnostic tool and provides repair information. The oxygen sensor unseats the formerly most common Check Engine light culprit: a loose gas cap. There are fewer reports of that problem because savvy motorists have learned to fix it themselves and consumers now buy new cars with capless gas tanks.
But don’t despair. Replacing your car oxygen sensor will keep you from wasting money by burning extra gas, and the repair isn’t horribly expensive. We know this firsthand. We had to replace the O2 sensor on our 1996 Lexus ES 300, the subject of our Debt-Free Car project, and it wasn’t as much of a hassle or expense as we had feared.

What does the O2 sensor do?

It is the primary measurement device for the fuel control computer in your car to know if the engine is too rich or too lean. The O2 sensor is active anytime it is hot enough, but the computer only uses this information in the closed loop mode. Closed loop is the operating mode where all engine control sensors including the Oxygen sensor are used to get best fuel economy, lowest emissions, and good power.

Should the O2 sensor be replaced when the sensor light comes on in your car?

Probably not, but you should test it to make sure it is alive and well. This assumes that the light you see is simply an emissions service reminder light and not a failure light. A reminder light is triggered by a mileage event (20-40,000 miles usually) or something like 2000 key start cycles. EGR dash lights usually fall into the reminder category. Consult your owners manual, auto repair manual, dealer, or repair shop for help on what your light means.

How do I know if my O2 sensor may be bad?

If your car has lost several miles per gallon of fuel economy and the usual tune up steps do not improve it. This *is not* a pointer to O2 failure, it just brings up the possibility. Vacuum leaks and ignition problems are common fuel economy destroyers. As mentioned by others, the on board computer may also set one of several failure “codes”. If the computer has issued a code pertaining to the O2 sensor, the sensor and it’s wiring should be tested. Usually when the sensor is bad, the engine will show some loss of power, and will not seem to respond quickly.

What will damage my O2 sensor?

Home or professional auto repairs that have used silicone gasket sealer that is not specifically labeled “Oxygen sensor safe”, “Sensor safe”, or something similar, if used in an area that is connected to the crankcase. This includes valve covers, oil pan, or nearly any other gasket or seal that controls engine oil. Leaded fuel will ruin the O2 sensor in a short time. If a car is running rich over a long period, the sensor may become plugged up or even destroyed. Just shorting out the sensor output wire will not usually hurt the sensor. This simply grounds the output voltage to zero. Once the wiring is repaired, the circuit operates normally. Undercoating, antifreeze or oil on the *outside* surface of the sensor can kill it. See how does an Oxygen sensor work.

Will testing the O2 sensor hurt it?

Almost always, the answer is no. You must be careful to not *apply* voltage to the sensor, but measuring it’s output voltage is not harmful. As noted by other posters, a cheap voltmeter will not be accurate, but will cause no damage. This is *not* true if you try to measure the resistance of the sensor. Resistance measurements send voltage into a circuit and check the amount returning.

How does an O2 sensor work?

An Oxygen sensor is a chemical generator. It is constantly making a comparison between the Oxygen inside the exhaust manifold and air outside the engine. If this comparison shows little or no Oxygen in the exhaust manifold, a voltage is generated. The output of the sensor is usually between 0 and 1.1 volts. All spark combustion engines need the proper air fuel ratio to operate correctly. For gasoline this is 14.7 parts of air to one part of fuel. When the engine has more fuel than needed, all available Oxygen is consumed in the cylinder and gasses leaving through the exhaust contain almost no Oxygen. This sends out a voltage greater than 0.45 volts. If the engine is running lean, all fuel is burned, and the extra Oxygen leaves the cylinder and flows into the exhaust. In this case, the sensor voltage goes lower than 0.45 volts. Usually the output range seen seen is 0.2 to 0.7 volts. The sensor does not begin to generate it’s full output until it reaches about 600 degrees F. Prior to this time the sensor is not conductive. It is as if the circuit between the sensor and computer is not complete. The mid point is about 0.45 volts. This is neither rich nor lean. A fully warm O2 sensor *will not spend any time at 0.45 volts*. In many cars, the computer sends out a bias voltage of 0.45 through the O2 sensor wire. If the sensor is not warm, or if the circuit is not complete, the computer picks up a steady 0.45 volts. Since the computer knows this is an “illegal” value, it judges the sensor to not be ready. It remains in open loop operation, and uses all sensors except the O2 to determine fuel delivery. Any time an engine is operated in open loop, it runs somewhat rich and makes more exhaust emissions. This translates into lost power, poor fuel economy and air pollution. The O2 sensor is constantly in a state of transition between high and low voltage. Manfucturers call this crossing of the 0.45 volt mark O2 cross counts. The higher the number of O2 cross counts, the better the sensor and other parts of the computer control system are working. It is important to remember that the O2 sensor is comparing the amount of Oxygen inside and outside the engine. If the outside of the sensor should become blocked, or coated with oil, sound insulation, undercoating or antifreeze, (among other things), this comparison is not possible.

How can I test my O2 sensor?

They can be tested both in the car and out. If you have a high impedence volt meter, the procedure is fairly simple. It will help you to have some background on the way the sensor does it’s job. Read how does an O2 sensor work first.

Testing O2 sensors that are installed

The engine must first be fully warm. If you have a defective thermostat, this test may not be possible due to a minimum temperature required for closed loop operation. Attach the positive lead of a high impedence DC voltmeter to the Oxygen sensor output wire. This wire should remain attached to the computer. You will have to back probe the connection or use a jumper wire to get access. The negative lead should be attached to a good clean ground on the engine block or accessory bracket. Cheap voltmeters will not give accurate results because they load down the circuit and absorb the voltage that they are attempting to measure. A acceptable value is 1,000,000 ohms/volt or more on the DC voltage. Most (if not all) digital voltmeters meet this need. Few (if any) non-powered analog (needle style) voltmeters do. Check the specs for your meter to find out. Set your meter to look for 1 volt DC. Many late model cars use a heated O2 sensor. These have either two or three wires instead of one. Heated sensors will have 12 volts on one lead, ground on the other, and the sensor signal on the third. If you have two or three wires, use a 15 or higher volt scale on the meter until you know which is the sensor output wire. When you turn the key on, do not start the engine. You should see a change in voltage on the meter in most late model cars. If not, check your connections. Next, check your leads to make sure you won’t wrap up any wires in the belts, etc. then start the engine. You should run the engine above 2000 rpm for two minutes to warm the O2 sensor and try to get into closed loop. Closed loop operation is indicated by the sensor showing several cross counts per second. It may help to rev the engine between idle and about 3000 rpm several times. The computer recognizes the sensor as hot and active once there are several cross counts. You are looking for voltage to go above and below 0.45 volts. If you see less than 0.2 and more than 0.7 volts and the value changes rapidly, you are through, your sensor is good. If not, is it steady high (> 0.45) near 0.45 or steady low (< 0.45). If the voltage is near the middle, you may not be hot yet. Run the engine above 2000 rpm again. If the reading is steady low, add richness by partially closing the choke or adding some propane through the air intake. Be very careful if you work with any extra gasoline, you can easily be burned or have an explosion. If the voltage now rises above 0.7 to 0.9, and you can change it at will by changing the extra fuel, the O2 sensor is usually good. If the voltage is steady high, create a vacuum leak. Try pulling the PCV valve out of it’s hose and letting air enter. You can also use the power brake vacuum supply hose. If this drives the voltage to 0.2 to 0.3 or less and you can control it at will by opening and closing the vacuum leak, the sensor is usually good. If you are not able to make a change either way, stop the engine, unhook the sensor wire from the computer harness, and reattach your voltmeter to the sensor output wire. Repeat the rich and lean steps. If you can’t get the sensor voltage to change, and you have a good sensor and ground connection, try heating it once more. Repeat the rich and lean steps. If still no voltage or fixed voltage, you have a bad sensor. If you are not getting a voltage and the car has been running rich lately, the sensor may be carbon fouled. It is sometimes possible to clean a sensor in the car. Do this by unplugging the sensor harness, warming up the engine, and creating a lean condition at about 2000 rpm for 1 or 2 minutes. Create a big enough vacuum leak so that the engine begins to slow down. The extra heat will clean it off if possible. If not, it was dead anyway, no loss. In either case, fix the cause of the rich mixture and retest. If you don’t, the new sensor will fail.

Testing O2 sensors on the workbench.

Use a high impedence DC voltmeter as above. Clamp the sensor in a vice, or use a plier or vice-grip to hold it. Clamp your negative voltmeter lead to the case, and the positive to the output wire. Use a propane torch set to high and the inner blue flame tip to heat the fluted or perforated area of the sensor. You should see a DC voltage of at least 0.6 within 20 seconds. If not, most likely cause is open circuit internally or lead fouling. If OK so far, remove from flame. You should see a drop to under 0.1 volt within 4 seconds. If not likely silicone fouled. If still OK, heat for two full minutes and watch for drops in voltage. Sometimes, the internal connections will open up under heat. This is the same a loose wire and is a failure. If the sensor is OK at this point, and will switch from high to low quickly as you move the flame, the sensor is good. Bear in mind that good or bad is relative, with port fuel injection needing faster information than carbureted systems. ANY O2 sensor that will generate 0.9 volts or more when heated, show 0.1 volts or less within one second of flame removal, AND pass the two minute heat test is good regardless of age. When replacing a sensor, don’t miss the opportunity to use the test above on the replacement. This will calibrate your evaluation skills and save you money in the future. There is almost always *no* benefit in replacing an oxygen sensor that will pass the test in the first line of this paragraph.