scooby@goole

just been and bought a universal sensor. it is 3 wire one like my original, but on the instructions it says that if on the original item a wire is red,yellow or blue it is advisable not to use a universal one. my scooby one is red,white and black. does anybody have any ideas why you wouldnt be able to use it.

ollo

They give this warning because there are 2 types of lambda sensors - Zirconia (more common) and Titania sensors. They are not interchangeable. Titania 3-wire sensors generally have red/black/white wires, but apparently some Zirconia sensors do as well. Subaru sensor is one fine example of Zirconia sensor that has red/black/white wires and is perfectly interchangeable with universal Zirconia sensors.
2 of the wires that have the same color on the universal sensor are heater wires, third wire (different color) is the signal wire. Polarity of heater wires does not matter on Zirconia sensors. I can't remember which one was signal on the Subaru sensor, but it was easy to find out on my Legacy, as the signal connector was gold plated, heater connectors were silver plated. I believe some Imprezas have separate connector for signal(1 wire) & heater (2 wires).
You can also unplug the sensor and measure voltages with digital voltmeter on the ECU side. Heater wires will be +12 and zero V, signal wire will show ~0,45V without sensor connected (reference voltage from ECU).

[Edited by ollo - 12/10/2003 7:42:05 PM]