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View Full Version : AF Sensor or O2 Sensor?



doug2168
07-20-2008, 10:15 AM
ok, i have this civic that i'm trying to lean out to get better gas mileage out it. i posted in another thread asking about logging software for it. well it turns out the software i had wasnt giving me all the data i needed BUT it was correct. so, if anyone doesn't want to spend the 200.00 like i just did on a scan tool to get this data and be able to deal with obd2 issues in your civic, just build a "jeff interface" for 20.00, get the wiring pinout of your obd2 connections and you're on your way using your laptop to read codes, clear codes and get "some" useful live data from your car.

now, my question for the people in this forum is this: i purchased a nice mid quality scan tool, i have no codes but like i said i'd like to lean out my mix by modifying the IPW (injector pulse width). don't let this throw you off my question though. i just need to know what the voltage reading should be on the upstream o2 sensor on my 05 civic. this is not a hybrid civic. it's just a plain run of the mill vp.

i've taken my DVOM and read all the wires to gnd and this is what i get: black 12v, black 0v, green 1.6v, white 2.2v. now the white is showing AFS + in the wiring diagram and green is AFS -. the 2 black wires are the heater. ok, no problem so far.

here's the thing though....is this an air/fuel sensor or an oxygen sensor??? i question this because of a couple of things, first being the voltages, second being the schematic calling it an AF sensor. what should the readings be for either sensor??? again there are no codes being thrown, gas mileage is the same it was after driving off the lot, doesn't run rough, lots of power still.

here's more to throw at ya. when connecting the scan tool and bringing up live data i am getting the downstream o2 sensor reading on avg .760v at idle and the upstream reading is in milli-amps and reads .446 mA on avg. what's with this???

allof the mechanics i've talked to say i have a problem somewhere because the upstream sensor should read .450v period. it should fluctuate a bit but avg should be .450v. i understand this IF it were an actual run of the mill o2 sensor but i'm wondering what i REALLY have.

i hope there's someone knowledgeable enough out here to help me understand this.
i'm betting on an AF sensor but, i'm wondering if the resistor mod will work as per the "tuning for mileage" document.

i'm trying to be as careful as possible with my vehicle so i don't blow anything up. i want to fully understand what's going on and grasp the concepts before modding anything.

tia