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post #1 of 5 Old 10-19-2012, 04:01 AM Thread Starter
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Quick question re: rear O2 heater circuit function

This is probably a stupid question, but thought I would post and ask rather than assume anything. I know that O2 sensors are kept heated in order to, at least partly, keep them clean and keep anything from forming on the sensor itself. Since I removed my cats and put on an offroad X-pipe, I turned off the O2 sensors with my SCT Xcal2 to avoid throwing a code, but this question occured to me while I was replacing the O2 on a friend's truck. If you are turning off the sensors in the tune, does the sensor still get heated and work just like normal, but that no signal is sent to the EEC? If they are NOT heated when turned off, which is what I am assuming is the case, then they could get carbon and other stuff forming on the sensor which would result in erratic readings when the sensors are turned back on for smog time or other diagnostic work.

Anyone know for sure what happens exactly when they are turned off/removed from the EECs tuning tables?

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post #2 of 5 Old 10-19-2012, 01:22 PM
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I can't say for 100% certainty, but I'm pretty sure that turning them off in the tune simply tells the EEC to ignore them. I don't think think the EEC physically turns them off/on.

With that being said, you always thread one out, start the car and see if it heats up. Should heat up pretty quickly, and I want to say it gets pretty hot.


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post #3 of 5 Old 10-21-2012, 07:24 AM Thread Starter
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Quote:
Originally Posted by 93Cobra#2771 View Post
I can't say for 100% certainty, but I'm pretty sure that turning them off in the tune simply tells the EEC to ignore them. I don't think think the EEC physically turns them off/on.

With that being said, you always thread one out, start the car and see if it heats up. Should heat up pretty quickly, and I want to say it gets pretty hot.
I assume that this test would be completed by hooking up the elec connectors to the O2 as usual, but NOT threading it into the pipe and just see if it gets above ambient temp, right?

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post #4 of 5 Old 10-21-2012, 10:19 AM
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Correct. Perhaps even easier would be to start with the plug off, and probe with a volt meter and see if voltage is coming to the heater circuit.

Heck, this is assuming the back o2 has a heater circuit. I'm assuming it does but don't know for a fact. Perhaps a little parts research is in order too.

I guess easier version is to check for voltage or heat first.


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post #5 of 5 Old 12-04-2012, 08:13 PM
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Does the EEC control the O2 heater circuits? since they're not wideband sensors and the EEC doesn't need to control the heaters, I would guess that they have power whenever the key is switched to RUN. Try consulting a wiring diagram to be sure.

They will produce a signal voltage anyway by nature of design; even single-wire sensors do that. It doesn't matter is the EEC is connected or not. They're just not accurate until up to operating temp, which is mostly what the heater is for.

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