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Discussion Starter · #1 · (Edited)
Hello everyone, I have a Mazda 3, 2.0L 2009 Gen-1 Sedan Automatic & a couple of months ago I noticed that the car was running rough and had a noticeable lack of power and acceleration with no codes. I started & checked all the obvious; air filter, plugs, throttle body, maf sensor, earthing, fuses & so on. Then one of my friends who use to have a 3 told me that the O2 sensors can sometimes fail with no codes. He suggested that I disconnected the cable to the upstream O2 sensor & see what the result would be.

I did that & the car ran smoother @ idle & during driving but still lacks power & its usual "zoom zoom" of course then the orange engine light came on to indicate the O2 not being detected. Anyway I then started looking at the O2 sensor in more detail:

I bought an O2 sensor removal socket & removed it, it's a 5-wire non-California original O2 sensor part number: LFL7-18-8G1 then I tried to check the sensor (for resistance) using a multi-meter but the Mazda tech manual is confusing and it says that the terminals C & D should be checked for resistance.

My 5-wire upstream O2 sensor (as you look at the connector with the clip on top as shown in the tech manual) is wired as follows:


E = Yellow
C = No wire connected
A = Blue
D = Black
F = Grey
B = White

& the point is that I can't check C & D which I assume are supposed to be the heater wires for resistance as there's no wire in C.

Can anyone tell me what each of the above colors are for please.

Any help would be much appreciated.
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