Anyone replaced their O2 sensors without connectors? There's four wires and two are white...are these two interchangeble?

 

i'll check the book . are you thinkin' these are the grounds/?

 

I have no idea They're both white...

 

here's what the book says;pre -cat;red/white=fuse 15 amp blk./green= heater for sensor. yellow =varistor. black =return for varistor. post cat ; red/ green= fuse 15 amp; blue /red =heater.;blue/ yellow =varistor . blue/green = return for varistor.sorry i don't see two whites.

 

the book sucks it shows only three wires each at the dme then four wires at the o2's but doesn't show the place where the forth wire goes.

 

okay ;the three going to the dme are function the fourth is just feed . you need to figure if the two white s go to the variable resistor or to the heater. then it's easy . the trouble is i don't know what you should get for ohms with a cold sensor. if we knew we could get you going.the heater will have fixed ohms but so will the varister . is one wire thicker than the others. 15 amps is alot.

 

Thanks Herbie...but I guess I shoulda thought of that before I snipped the cable What would they have two identical white wires if they're going to serve different function?

 

exactly. what color is the third and fourth ? maybe some of it holds true to book. i'm thinkin' the whites are either the power and heater or the sensor part. the wire size ;if different would tell that maybe.

 

two of the wires to the dme are sheilded. these are your sensor wires. they're more likely to be smaller.(pre-cat). post cat shows no sheilds. these are loops so the exact wire for each pair won't matter. you just gotta seperate the pairs.

 

the white wires are for the sensor.. Gray and black are for the heater. Check out the sight for o2 simular .. great write up on it

 

Is this at NAM or O2simulator.com?

 

That sounds familiar; the two white wires being for the signal. It's best to look further upstream on the wiring harness so you can match the wire colors that are in the Bentley book: Electrical diagrams 78 and 79. No promises on avoiding a CEL though if you don't have the heater simulated also, as there is a code in the book for one.

 

1-black=signal
2-gray=ground
3-white=heater
4-white=heater


One of the white is +12V...what's the other one for then? WTF???

 

White wires are for the heater - the heater is not polarity sensitive, it's just a resistive element. The black wire is the sensor output. The gray wire is the sensor return, or ground. Back in the day (old fart mode ON) o2 sensors had simply one output wire and were grounded through the sensor body. It was soon determined (and made a requirement) that emission systems go into closed-loop operation sooner after startup, so a heater was added to the sensor to bring it up to the 600 or so degrees needed for proper operation faster than relying on the exhaust to heat it up. The heater usually added two more wires to the sensor, up to three. These days, with the need for high accuracy in feedback mode, the sensor ground was isolated from the electrically 'dirty' chassis ground and sent back to the ECU separately, hence the 4th wire.

Since the heater is not needed after the sensor warms up fully, and would actually overheat the sensor if it were to remain on, the ECU shuts off the sensor heater a while after the engine has been running. This is generally done by opening the return (grounded) lead coming from the sensor heater. So, that's why you have +12 and (indeterminate) leads. the (indeterminate) is actually switched.

 

That's very informative Greatbear My precat sensor was seized to the header and I had to snip the wires in order to remove the header. When I go back to solder the black to black, gray to gray, does it matter which white goes with the other whites as there are two?

Also, do you feel that a "universal" four lead O2 sensor is as good as OEM?

 

I've dealt with aftermarket O2s before, they are never as good as the OE ones.

 

Partsman Do you happen to know how much the OEM precat sensor is?

 

$189 from minicarparts.net. You also might want to try Classic MINI or one of the other dealerships that advertise on NAM.

 

My cost from the place I deal with is $160.65 plus tax.

 

I guess it couldn't hurt to try the $22 version first or do you think it's a waste of time?

 

All depends how many times you want to do it.
You can try splicing in the $22 dollar one, and see if throws a code.
or you can plug in the OE one and be done with it.

EDIT: whichever one you use, put some never seize on the threads so you don't have to chop the connectors off anymore

 

Bump? Calling Greatbear....

 

If you're going to use an aftermarket one, at least go with a good one...
http://www.boschautoparts.com/RB.NA....2003&Make=MINI

 

Thanks Joaquin

 

I've had varying luck with aftermarket sensors. Ones marked by Bosch or Seimens are pretty close to OEM or sometimes better, no-name ones are a crapshoot. Sometimes you get a good one, other times you get calibration issues or thrown codes for your efforts.

Partsman knows his stuffs, he didnt get the username for nothin'!