more info sa atong oxygen sensor
undefined Technically speaking, your oxygen sensor is a battery, it uses fuel and oxygen to create a voltage. It DOES NOT need a voltage input to create an actual reading
Question, "Why do some sensors have more wires than others?"
The answer is because they are heated, and to reduce interference. So, why do they need to be heated when they're in the exhaust stream? Early sensors were located in the manifold and thus didn't really have a problem heating up being so close. The drawback was, it didn't really recieve that good of an indicator as to what was really going on due to it sometimes only coming in contact with a couple cylinder's gasses. Over time, engineers realized that the oxygen sensor would read better if it was placed further away where the sensor could get a better mix.
The problem that was encountered after this was that the sensor didn't like to heat up fast enough. There are two problems with this,
1. the engine basically must assume the engine is lean and run rich to avoid damage, running rich is worse for the environment, and we want to cut this time as short as possible.
2. an oxygen sensor is damaged by being exposed to fuel when it isn't heated. SO, the sensors had to be replaced earlier sometimes as early as 45k miles.
All newer oxygen sensors are good for about 100,000 miles our more. Federal law states a vehicle manufacturer must replace ANY emmissions equipment that fails before 8 years or 80,000 miles regardless of how many owners there have been. So you can see why they'd not want this.
So here's the different wire setups
1 wire - One wire for the signal to the computer, sensor grounds through the exhaust
2 wire - One wire power for heater power, one is the signal to the computer, sensor grounds through exhaust
3 wire - One wire for heater power, one for heater ground, one for the signal to the computer, sensor grounds through exhaust
4 wire - One wire for heater power, one for heater ground, one wire for signal to the computer, one wire for grounding the sensor itself
5 wire - WB (we'll not be discussing this issue)
The heater is always on and runs through the same circuit as your fuel pump. SO as you can see, if you can screw it into your exhaust, you can make it work by wiring it up.
Bad grounds to the engine
What can a bad engine ground do to me then? Well, as you probably know, exhausts are suspended on rubber hangers, so the exhaust (and in turn your 1 through 3 wire sensors) ground through the engine. SO if you don't have a good ground to your engine, your O2 sensor is not going to work right.
Testing your sensor
So now that you know how it works, we'll discuss testing it. All you need to do is look at your wiring diagram for your car and figure out the sensor wire. Your going to have to stick a pin or something through the sensor wire to keep the car running as it should. YOU MUST HAVE A METER WITH HIGH INTERNAL RESISTANCE FOR THIS ONE.
If you expect a bad O2 and your sensor is heated, we're gonna test both the sensor and the heator (if it's not skip to the testing the actual sensor paragraph).
Testing the heater circuit
Most oxygen sensors (read MOST) are PTC thermistors, don't know what this means? See my coolant temp sensor article. So, you can see, as your sensor heats up, it'll probably raise the resistance (but it COULD lower it)
1. Figure out which 2 wires are the power and ground for the 02 heater circuit. Cut the wire to the power far enough from the sensor that you can resplice the ends together when you're done.
2. Splice the ends, and using a test light as an ammeter hook one of the cut wires to one wire of the test lamp, and the other to the other wire of the test lamp.
Testing the actual sensor
1. Find the wire that sends the information to the computer.
2. Push a pin or something small but sharp through the center of the wire.
3. Using a meter with internally high resistance (See my DVOM article) hook one lead to the sensor to the computer wire hook the other lead to a chassis ground, if you have a 4 wire sensor, you need to push a pin through the sensor ground too and hook the other lead to it.
Start the vehicle, it must be noted that the sensor needs to get hot. If you're running a non heated oxygen sensor, you need to just wait until you think it's hot, probably 5 minutes is more than sufficient. If it's heated the bulb will probably start out really bright, and dim itself (but it might go the other way). Either way you need to wait until one of these two things happens. If it doesn't happen, check that the heater circuit is even getting power to it with the voltmeter, if it is, and the heater part is bad and it must be changed out.
Once the sensor is warm, you can begin paying attention to the vehicle. So, if you don't have electronic fuel injection, then you need a small propane torch, induce propane into the intake so the rpm drops by a couple hundred RPMs. If you do have EFI, just unplug the vac signal to the fuel pressure regulator and plug the line. The voltage should shoot (not drift) up above .8 V. Now, unplug the hose that powers the fuel pressure regulator so it creates a vacuum leak, the voltage should drop below .2 V.
If you KNOW that your air fuel mixture is RIGHT, with everything hooked back up, look at the reading with the vehicle at 1500 rpms. It should be right around half a volt.
If you got this far with it, the O2 sensor is probably good, if not, it may not be bad. Check the grounds, also, the sensor draws air from where the wires go into the sensor, if this is plugged with dirt you need to clean it.