T-train

Ok, my 90 civic winter beater gets a check engine light about 10 min into driving anywhere. If I stop, shut off the car and start up again, it comes on again anywhere from 5 to 10 min later.
It never did it before I did my head gasket, now it happens all the time.
The engine code is 1 - oxygen content. The trouble shooting guide says to check the O2 sensor. How the hell are you supposed to check it?
Also..........can I pass an E-test with a hole in the gas tank? It passed safety with a 1/4 tank of gas.
I think that it might not due to a vacumm issue.

red90dx

make sure its pluged in, I think if you use a volti-meter on it, it will give a reading..... using <ohm>

bbarbulo

iTrader: (2)

red90dx, you are not supposed to test an O2 with a regular multimeter - apparently it fries them. in the books it says to use a special o2 tester.

as for e-test with a hole - what they don't know won't hurt them... be sure you haven't overfilled, and the emissions numbers won't change at all.... if they notice then you'll fail the visual inspection.

imported_gatherer

an Oxygen Sensor is a special type of Diode. The output of the O2 sensor is between 0 and 1 volts. the difference comes when it's in a state called stoichiometric. For all Zener Diodes (and the O2 sensor is special sub branch of them) the Stoichiometric point is the break down point or the point the diode goes from letting no current tot he point where it lets all (save a bit because of a small voltage drop) current through. Ussually this is a certain voltage level that the Zener Diode is rated at. in the Case of the O2 sensor, it's not a voltage that triggers this but a Air/ unspent fuel ratio. ussually it's around 14.7:1.

The O2 sensor will go from outputing minimal current before this to dumping most of the current just after this ratio. so at 14.8:1 not much current will get through. but at 14.6:1 lots of current gets through. the change over point will change the voltage over the diode by as much as 85% during that small window.

now how does this help the ECU monitor air/fuel ratio. Well the ECU is a computer. it's small and not very powerful, but it still is a computer. with that said the ECU has limitations. one such limitation is the ECU only understands zeros and ones. The ECU will be able to understand the O2 sensor since the O2 sensor is bouncing from 1 to 0 volts (this does get magnified in the ECU circuity to be a standard 0 or 5 volt TTL logic) and based on that the ECU knows that when it's a 1 the car is richer and when it's a 0 it's leaner then the 14.7:1 ratio.

there is some more complex stuff that happens with newer sensors. this is for the 3 wire or 2 wire O2 sensor. anyways I hope this helps.

ohh and yes bbarbulo's right NEVER CHECK A DIODE WITH A MULTIMETER BY CHECKING RESISTANCE YOU WILL FRY IT

T-train

Hmmm, well all that info is nice, but it doesn't get me any closer to an answer of how to "check" it. As I was saying before, it worked fine before I changed the head gasket, and now the engine light comes on everytime I drive.

imported_gatherer

well first check for lose wires... or a disconnected sensor then get an actual O2 sensor tester like bbarbulo suggested...

the other thing you can do is measure the voltage drop while the car is running but thats always changing and is hard to tell whether it's in spec or not.