'98 OBW o2 sensor confusion

[hankosolder2]

I purchased a replacement rear o2 sensor for my '98 OBW, due to a rear O2 sensor code. (The old one is obviously bad- the wires are cracked!)

 

I bought an "oe exact fit replacement o2 sensor." (It's DENSO brand.) It's got a four pin connector on it (as does the original one.) The difference is that the original o2 sensor has only three wires going to the connector (one pin of the four pin connector is unused.) The replacement o2 sensor has four wires coming out of the sensor itself and they all go to the connector. The connectors appear to be the same shape... I'm wondering if the 4th wire is somehow redundant? I can't tell if the "car end" of the connector actually has wires going to each pin. Maybe I should ohm it out. Any ideas, folks?

 

NAthan

[Cougar]

I think one pair of wires on the new sensor is for the element and the other pair is for the heater. The origninal sensor may have grounded one side of the heater circuit to the sensor body and so only needed one wire to the heater. If this so you will need to ground one of the heater wires to make it work. See if you have some resistance to the old sensor body on one of the three wires. If so then I think what I stated is correct. The resistance will be fairly low, maybe around 10 ohms.

[hankosolder2]

Thanks, Cougar. I understand what you're getting at... the 3 wire sensor must have one wire for a positive supply for the heater, one wire for the output for the sensor and one wire for ground, which is presumably shared by the heater and the sensor element- unless they are using the body of the o2 sensor for the ground for one of the two functions.

 

I think the four wire sensor has separate, isolated grounds for each section...i.e. a ground for the sensor element and a ground for the heater.

 

I don't want to hack the wiring as this was supposedly an OE, plug in ready sensor, so I contacted the supplier to see what they have to say for themselves. The only way I can see it working properly as-is is if there's an internal connection between the two grounds in the body of the sensor or if one of the grounds is bonded to the body of the sensor. ('cause it definitely won't work right if one of the sections of the sensor is left floating.) Unfortunately, I can't do a continuity check on the new sensor as opening the bag renders it unreturnable.

[Cougar]

Check the old sensor and see if there is continuity between one of the wires and the body of the sensor. There may be a common ground to both circuits but I suspect it would be just for the heater. Also I seem to recall that you should never try to check the resistance of the O2 sensor as it may damage it. Though I wouldn't think a digital meter could do that but I don't know for sure. The heater portion is not a problem to check.

Edited May 17, 2009 by Cougar