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Hi,
Using Universal O² Sensors isn't an issue if you do your homework. There are 5 types of O² Sensors; Unheated Thimble-type O² Sensors (LS), Heated Thimble-type O² Sensors (LSH) , Heated Titania-type O² Sensors, Heated Planar-type O² Sensors (LSF), and Heated Wide-Band O² Sensors (LSU).
Further within these types, several different primary materials are used and two different methods of extrapolating the Air/Fuel Mix are used.
A sensor using Titania, changes it’s resistance of a reference voltage (sent to it by the ECU) which will change proportionally to the amount of Oxygen it is exposed to. This technology was never in widespread use and was found only on a few cars from the mid-80’s to mid-90’s. It is estimated that fewer than 3% of all cars and trucks use this type.
The most prevalent types of O² sensors on the Market are those which use a ceramic made of Zirconia. When exposed to Oxygen (O²), a Zirconia ceramic will produce a voltage proportional to the amount of Oxygen it is immersed in (Exhaust stream) as the Oxygen molecules embed into the ceramic’s surface. For the two types of Zirconia sensors, they need to be heated to 650°F. This further breaks them into two additional categories: Unheated and Heated.
Unheated Zirconia sensors generally have only one or two wires. Their advantage is that they are simpler to manufacture and are of the earliest technology. Their disadvantages are that they contaminate sooner (as carbon and other combustion by-products condense on the exposed ceramic) and on Cold Starts, don't allow the ECU to function until the exhaust gasses bring them up to their operating temperature (Open Loop). Also, if idling for extended periods, they can fall below their operating temperature threshold (650°F) and force the Car's ECU back into an Open Loop where the ECU is no longer monitoring or responding to changes in the A/F mix. This affects both emissions and performance.
Heated Sensors contain a Heat Coil which is fed by a separate voltage circuit and usually have 3 or 4 wires. Their advantages are that they come up to temperature sooner and don't stop monitoring at idle. Also, since they are heated, fewer contaminates can condense on the ceramic surface of the sensor giving them a longer service life.
Heated Planar-type O² Sensors (LSF) and Heated Wide-Band O² Sensors (LSU) are a much more modern technology and are used primarily on only the latest model cars. They use a circuit board with the sensors attached and use a pulse-width heater coil. Their advantages are that they operate at much higher temps (1292° to 1472° F) and will vary their voltages in much smaller increments allowing for direct sampling of the A/F mix instead of an extrapolation method used on the other types of sensors. I won’t discuss these in-depth except to say that the ’08 997TT uses the Heated Wide-Band O² Sensors (LSU) type. Hope this helps.
Zirconia O² sensors are the type used on the Boxster (Heated Thimble-type O² Sensors (LSH)). Because all air does not contain the same amount of Oxygen (changes in altitude, Ground Level in Stop & Go Traffic, etc.), Zirconia sensors also need to sample reference air. To do this, they either have a hole at the base of the detector, or sample air drawn-in from the electrical connector and sent to the sensor inside the wire sheathing.
This is where most people trying to use Universal Sensors will get into trouble. They will inadvertently block the reference air from the sensor by using the wrong connectors (which contain no sampling hole), kinking the sheathing, or by using heat shrink tubing and also blocking the sampling hole. When using Universal sensors, you need to carefully examine the new and old sensors. If the sampling hole is in the sensor body, there will be no problem. But, if the reference air sample is drawn into the connector, you need to make sure that you don’t interfere with this function when attaching a connector. The Bungs for O² sensors are standard, so virtually any Universal will work so long as you account for the air sampling to occur.
O² sensors have a usable life of only about 30k mi. (source: Robert Bosch, AG). After this, range (MPG), emissions, and performance can suffer. Changing them at this interval is one way to breathe new life back into your car and the cost is significantly offset by fuel savings. You should change all the O² sensors at the same time as they are mileage dependent. You can confuse the ECU (DME in Porsche parlance) by mixing new/old sensors causing a loss of range or performance. And, if you have 1 bad one, you'll soon see the others fail as well, especially if over 30k mi. of service, so it's just generally easier to do them all at once (save on S/H, installation, etc.). Hope this helps…
Happy Motoring!... Jim’99
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