HO2S troubles

mazda
mazda5

#1

Last month I dealt with a few engine codes, including a P0030/P0031, HO2S heater circuit. The sensor was old anyway so I up and replaced it, all the codes wiped, we were good. Now I have the codes again, one month later. I checked the wires with a multimeter and they’re fine. I REALLY don’t feel like undoing tons of wiring( these Japanese cars aren’t very maintenance friendly). Any ideas other than ECM?


#2

Bad O2 sensor maybe? Not unheard of.

Also check for a heater relay or fuse that is used on some vehicles. I’d suspect a relay given the return of the problem as a fuse would not be intermittent.


#3

unplug the sensor and check at the wiring for 12 volts at the heater circuit connector


#4

Don’t take this the wrong way . . .

Are you sure you replaced the correct sensor?

All modern cars have an upstream and downstream sensor

And if you have a V engine, you’re going to have at least 3, possibly even 4, sensors

And if you have a V engine, knowing your cylinder layout is critical. For example, if the code says Bank 1 sensor 1, do YOU even know which bank is bank 1 . . . ?

And if you have an inline engine, do you know the difference between sensor 1 and sensor 2? Sensor 1 would be upstream, sensor 2 would be downstream.

If’s actually quite common for the wrong sensor to get replaced


#5

yeah Im sure, my model only has one upstream and one down stream. And I know it was the right one because when I replaced it, the codes wiped and the engine ran MUCH better.

My multimeter has been giving me issues so got a new one. Tested again, and no resistance on the heater circuit. Dont buy cheap o2 sensors is the moral I guess