Honda Civic / Del Sol (1992 - 2000) EG/EH/EJ/EK/EM1 Discussion

o2 heater circuit is off and a/f ratio high

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Old Oct 30, 2011 | 06:22 PM
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milkwasabadidea's Avatar
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Default o2 heater circuit is off and a/f ratio high

So I got the chance to get some live data from the honda scan tool.... it said that my primary heater circuit was off...... I hooked it up when my car was still warming up and I let it warm up all the way and the heater circuit was off the whole time..... also my a/f numbers were high like 18.9-21 when its supposed to be like 13-15... my secondary o2 was working fine......the car is a 1998 hx.... with a ntk primary o2.... I pulled the primary out and its rich as hell...... my car isn't throwing any codes for the heater circuit either... so I'm stumped ....
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Old Oct 30, 2011 | 06:31 PM
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Default Re: o2 heater circuit is off and a/f ratio high

The ECU doesn't use primary O2 sensor inputs until the engine is fully warmed up.
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Old Oct 30, 2011 | 06:32 PM
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Default Re: o2 heater circuit is off and a/f ratio high

o2 sensor is bad... honda scan tool?
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Old Oct 30, 2011 | 07:16 PM
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Default Re: o2 heater circuit is off and a/f ratio high

Originally Posted by RonJ@HT
The ECU doesn't use primary O2 sensor inputs until the engine is fully warmed up.


I let it warm up and kept the car on while the scan tool was hooked up hoping the heater circuit would switch on... still the heater circuit should be on when I first start up the car... according to my instructor
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Old Oct 30, 2011 | 07:21 PM
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Default Re: o2 heater circuit is off and a/f ratio high

Originally Posted by Hidenplanvew
o2 sensor is bad... honda scan tool?

I'm guessing its bad. Imma whip out my multimeter soon to do some tests.. haven't gotten the time to do anything.... I'm just wondering why the heater circuit is off and there's no codes for malfunction.....

I forgot the name for the honda scan tool.. its hds something blah blah... connects to the dlc connector to get live data from the car and I jus hook up to a laptop and it basically shows all my readings for the sensors and what not
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Old Oct 30, 2011 | 07:23 PM
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Default Re: o2 heater circuit is off and a/f ratio high

Check whether the heater element power wire for the primary O2 sensor has battery voltage with the key in ON(II) and also measure the resistance of the heater element.
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