this is for testing the oxygen sensor itself. test across the terminals of the sensor- with it unplugged.
For the 2000 ProtĂ©gĂ© LX w/1.6L DOHC, from what Iâm seeing, the rear o2 sensor heater circuit spec is 15.7 ohms. The front sensorâs resistance depends on whether it is a Calif car or not. 5.6 ohm for Calif, 15.7 otherwise.
If OP wants the exact spec, OP will have to secure a factory service manual or stop by a Mazda dealership shop and ask.
tHE heater spec is 15.7 Ohms?
Then why does the autozone guide tell us to measure " 5-7 ohms across terminals c and d" (please read above) ?
George, based on the information provided would you deem the 02 sensor as not functioning?
What resistances do you measure for the front and rear O2 sensor heaters? Is yours a Calif car? Or non-Calif?
Canadian car ie. non calif
As I mentioned before for the rear I got 13.2 Ohms.
Once I am able to tear apart the front one I will provide that reading.
Thank You.
The spec Iâm seeing says âapproximately 15.7 ohmsâ. You measure 13.2 ohms, so the difference is 2.5 ohm. Your sensor is measuring 2.5/15.7 or 16% lower than the spec. I wouldnât guess that is out of spec, but the spec doesnât give any guidance on how far off it can be. So no way to tell for certain. You could go to an auto parts store and measure the resistances in 5 samples, so youâd have an idea how the resistances vary part to part. If they vary +/- 25 %, then youâd know yours is within spec most likely. Youâve got one more sample to measure anyway, the front sensor. fyi, the heater element is just a resistor, and electronics hobbyists know that resistors typically come in 1%, 5%, 10%, and 20% tolerance. The 20% tolerance version are the least expensive, but they still work fine in tolerance insensitive applications. Iâd say a heater circuit is a tolerance insensitive application.
sooo what you trying to say is I should buy a resistor? a 2.5ohm one? and install it?
Measure the resistance of other sensor and post back what that one is.
Why would you assume the front sensor would have the same readings as the downstream sensor?
Thatâs what the specs I found said. Except for the Calif versions of this car, the front and rear resistances have the same spec.
Going to the junk yard tommorrow to pull off downstream o2 sensors.
What tools do I need?
They are free.
Thanks
Went to the junk yard earlierâŠall the 02 sensors from the proteges were removed! vultures scour the junk yard for parts and then resell them at a profit.
Anyway, I measured the front o2 sensor:
- 12V on the lower left PIN
- 20ohms across the two black wires (different reading than the 13 ohms on the downstream 02)
This was unplugged.
So its the sensor or the wiring?
I think Deltron has left the building as he has not posted in over a month.
The fact that the front sensor measures 20 ohms and the rear only measures 13 ohms (when the specs say they should be the same) & you got proper voltage at the harness ok to both sensors suggests maybe there is indeed a problem with that rear sensor. I think at this point , if this was my car problem, Iâd probably replace the rear sensor and see if that solved the diagnostic code & engine warning light problem. I should say that before doing that â just saying what Iâd do â Iâd figure out a way to verify the voltage with the sensor plugged in is the same too, before ponying up for a replacement sensor. Another idea is to swap the sensors and see if the problem switched from rear to front. But thatâs probably more trouble that it is worth, given the difficulty of diddling with an 18 year old exhaust system.
Power = Squared(Voltage) / Resistance.
Running voltage can be considered around 14 Volts.
The difference between 20 ohm and 13 ohm is in ability for the internal sensor heater to draw 9.8W (20 ohm) and 15W (13 ohm) of power respectively.
It will not be exact, as resistance will change with temperature change, but it illustrates the point.
For me it would be a good reason to scratch my head and think âwell, if ECM complains it can not heat the sensor and I know sensor is 35% low on heater power, so maybe ECM has a point?â
Replace that goddamned sensor 
called mazda dealershipâŠthey say the front and rear sensors are not interchangeable!
For crying out loud , started thread May of 2017 - 77 posts . Just take the thing some place and have it fixed.
Thatâs correct. At least from what I see, they have different part numbers. The front one starts with ZM01, the rear with ZM02. But the resistance spec is the same front/rear. 15.7 ohms for both.
( The Calif version part number for the front starts with ZM03. )
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Most are not interchangeable, front and rear oxygen sensors have different cord lengths and different connectors to keep you from plugging them into the wrong connector.