How to convert 18mm O2 sensors for use on bikes with Molex connectors?
Ladies and Gentlemen,
let me see if I can get this one explained properly...
Background: For my 2012 Softail I bought an exhaust with 18mm O2 sensor threads, i.e. too big for the 12mm ones my bike uses currently. I was not able to find a plug&play 18mm set of sensors that come with the 4-pin Molex connector the Softails started using as of 2012. Fair enough, I thought, I had an old pair of 18mm sensors sitting on the shelf and was happy about something to do. So I went to the dealer and ordered the Molex connectors and the necessary terminals as per partsfinder, with the plan to rewire them so I can use them. That sounded all very easy, but as usual, some confusion arose.
The 2011 wiring diagram shows as follows (exemplary for the front sensor):
Wire 1 ends up in the ECM, pin 8, "Front O2 Sensor".
Wire 2 collects a few other sensors (among them the rear O2, TPS and IAT) and goes to pin 26 of the ECM, "5V Sensor Ground".
The 2012 wiring diagram for the front sensor looks like this:
Wire 1 collects a few other components (like active exhaust) before it goes into the BCM, pin L3, "System Power".
Wire 2 goes directly to the ECM, pin 2, "Front HO2 Heater Ground".
Wire 3 goes directly to the ECM, pin 17, "Front HO2 Sensor".
Wire 4 combines with its counterpart from the rear O2 sensor and some others (like in 2011, IAT, TPS, and now also ET) before ending up at the ECM, pin 9, "5V Sensor Ground".
My first problem here: The O2 sensor on my bike only has two wires coming out of it, a violet and the gray one, I cannot find the other two.
My second problem comes form the coloring above: I would simply have ignored wires #1 and #2 and connected the BE wire from the (2011!) O2 sensor to pin #3 and the GY/BK wire to pin #4. But if the coloring of the O2 sensor in the 2012 diagram is correct, it is attached to "System Power" via the violet (V) wire and again to "Front O2 Sensor" via the grey (GY) one. Looks to me like there is a mistake somewhere?
My third problem: So I went and purchased the 4-pin Molex housings and terminals (as per partsfinder) to get this done. The housings come in different colors (grey for the front and black for the back) and two different types of terminals are required: One is called "TERMINAL, socket #22 AWG" and has parts number 73307-10, the other is "TERMINAL, socket #22 AWG (gold)" and has parts number 72344-10. They look almost identical, certainly from the mating end, at least to my untrained eye.
Interestingly enough, one of each terminal goes in each of the housings, i.e. each housing uses two different kind of terminals. BUT: which terminal to use for which wire? No information at all in the wiring diagram, and there seems to be nothing obvious in the housing that would solve this one.
Finally, two questions:
Do the O2 sensors have a "plus" and "minus" or can the polarity also be reversed without any consequences?
Where can I get the kind of wire sleeving that is used for the O2-sensor wiring? I can't find anything quite like it, what I see is either completely PVC or this see-through braided stuff. Does this particular kind have a special name?
Thanks already for the help, have a nice weekend, niv
mr. beagle has the winning ticket
the price is lower i believe but auto parts store should have them
if you have two wire, then to go to newer 4 wire, you need a new ecu and that ='s $$$$$$$$$
without the heater circuits, the 4 wire is pretty much useless.
Two different sensors all together and what you are trying to do won't work. Everything is there in the ECM as for as pins. The problem will come in with trying to find a calibration that will turn on the heaters and recognize the sensors. 2011 cal level is in the 200's and 2012 is in the 300's and you will have a hard time loading a 300 level calibration into a 2011 ECM.
You can buy 12mm bungs and weld them or use suggested adaptors.
I should have put this in my original post, I want to avoid these 18-->12mm adapters, I am told by a tuner that the sensors then sit too far outside of the exhaust stream for reliable measurements.
The option of welding in 12mm bungs also crossed my mind, but having a pair of 18mm bungs sitting around, the rewiring seemed like like the least intrusive and most easily reversible option.
@hrdtail78: I don't understand the first part of your post: My (stock) 12mm O2 sensors definitely do not have four wires, only two. I am tempted to say the wiring diagram is inaccurate. There is no heating or anything like it.
Reading TTS' tuning guide on how these sensors work, it seems (at least the ones I am comparing here) are putting out the same voltage under the same circumstances, so this should not affect calibration at all.
Thinking of it, I may just try to imitate the same configuration of pins that my current 12mms sensors have in the molex connectors. And then see what happens...
01-07-2022, 05:13 AM
How to convert 18mm O2 sensors for use on bikes with Molex connectors?
