O2 Senson 3wire vs 4wire

conrod44 · Post by **conrod44** » 11 Jan 2010, 13:29

Hi Everybody...
I am new to this post and am glad to find a good Volvo Forum. Thank you for having me. I have driven Volvo's since 1982, owned 12 and counting and am particularly partial to the 240 Wagons. The technology and construction on the older models is fascinating. The greatest testament to my affair with Volvo's was revealed a couple of years ago when my son purchased a V70 Wagon to transport his wife and young family. Which model is the fastest remains unresolved.

If you would allow, I would like to put forth a question regarding my 91 940T. I have tracked my check engine light using the OBD to the O2 sensor. The existing sensor contains 3 wires.... 2 white and 1 black. The new sensor I ordered (in haste and excitement) has 4 wires... 2 white, 1 black and 1 gray. Is there a down side to installing the new sensor splicing only the 2 white wires and the 1 black wire while leaving the gray wire capped and disconnected? I am thinking that the gray wire is intended for another destination and if the vehicle does not have that destination installed, the grey wire is irrevellant. I would appreciate your thoughts.

Post by **matthew1** » 11 Jan 2010, 14:51

Hi & welcome, conrod44, I moved your post to the 940 forum. It'll get a better response here regarding your O2 question.

conrod44 · Post by **conrod44** » 11 Jan 2010, 15:01

Thank you very much.

Post by **billofdurham** » 11 Jan 2010, 16:07

Is there a down side to installing the new sensor splicing only the 2 white wires and the 1 black wire while leaving the gray wire capped and disconnected?

Just a little one. The grey wire is usually the earth (ground) so it wouldn't work.

On Bosch and BDW sensors with that colour wiring the wires are:
Black - signal.
Grey - earth.
White - heater positive.
White - heater negative.

There is very little to gain by using a four wire sensor in place of a 3 wire, apart from a headache trying to work out the wiring.

I understand that you can use either white wire as the positive and the other one has to be run to a sound earthing point. I would be tempted to piggy-back it to the grey wire, but that is for you to decide.

Bill.