director59

How can
I test the A/F sensor/heater on my 2002 RX 300? Which of the 3 wires do I test and what should the measurement be?

TrueGS300

What's the code? If its for the heater circuit you might as well just put a new o2 in. They must fail by design eventually, its normal. But I can understand wanting to test it. You check for ohms on the heater circuit. When they go bad, generally its just an open reading. But the sensors should be 4 wire, not three.. are you sure of what you are looking at?

director59

I have 3 P1135, P1155, C1201

TrueGS300

Check your fuses first, because I'm not sure if these cars have an o2 fuse. GM does this and when say both upstream o2s or downstream o2s throw codes at the same time, it can be a blown fuse depending on how the heater circuit is failing. Usually one sensor will fail and cause the fuse to blow from shorting inside. This will make both o2s throw codes when the fuse blows. But this is rare. What I'm saying is that if there is a blown fuse, expect at least one sensor to be bad and the cause. But if there isn't a fuse for them, its also not uncommon for both heater circuits to fail. This can happen in yearly temp changes - winter to summer. I suspect that you just need to replace the upstream o2s.

But to test them, you either need to be able to see live data and watch voltage readings. Or ohm test them by disconnecting the sensors and checking the resistance on two of the terminals. kinda hard to explain on here.

Audiqv8

Live data with a scan tool.

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enshiu

did you reset the ecu yet?