Oxygen sensor voltage?

HISSIN50 · Dec 13, 2004

leakyfaucet said:
Ahh! No! You're the best chance I've got! Okay, the last thing I did was put the positive prong on my voltmeter into the back side of the left oxygen sensor wire going directly into the female end of the main harness that plugs into the computer (basically I tapped directly into what the computer would see), and I put the left prong from the voltmeter on the ground right next to the computer.

That make sense? That's all I did. While I was there, since I got no voltage, I flipped the switch to display resistance, and got 30 ohms.

So now that you're back with me, should I test the oxygen sensor directly? Would that even work?

ok, if you're a glutton for punishment, ill post some more.
BTW, Joe and Giddyup are your best chances at figuring this out, not I. that does not stop me from trying though.

i am familiar with the principles of an EGO and HEGO but not conversant with wire colors, so i wont address any of that (whew!). your post is very articulate and i totally get what you did (the way i read what you did, is called backprobing). that is the way to do it, and i think Joe mentioned something to the same effect. right on.

ok, so no volts. are you real sure you had the right wires? confusion could come from testing at the sensor (as the heating element wires are present there), but with you testing at the puter, it should be a no brainer - im sure you got it right on! (im thinking aloud, since my thinking is so poor tonight - this allows you to follow along and spot the flaws i make).

the sensor need to be at around 500*F, as i recall, to 'light off'. assuming this is true (should take a minute or two (or less), if the HEGO's are working - the HEGO ground is sometimes not attached at the back of the motor). otherwise, light off can take longer (which is why i mention all that).

what i might do at this point (see if others think this is a decent idea): since you got no juice at the puter, go to the sensors themselves and check volts and/or resistance (i think J and G will have ideas for you on how to best do this). if you show something at the sensor and not at the puter, that suggests an open in the wire (i think). BTW, i think the ground for the EGO is in the injector harness - ask Joe to be sure.

that is about all i can think of, and all i dare say at once! i take pride in trying to be somewhat articulate and precise, but not so on this thread - sorry to have made a mess of the thread. good luck with it!

leakyfaucet · Dec 13, 2004

My heater ground is definetly connected to where it should be. Whether or not there is a short or open in the wire, I don't know. What I do know is that I tried turning the ignition switch to ON and seeing if the sensors would heat up to where I could feel it. They didn't. I don't know if they're even supposed to when the engine isn't running or if only the tip heats up, all I know is that they didn't get warm to the touch.

I pulled off the oxygen sensor harness and tested the prongs on the connector from the main harness that connects to the oxygen sensor harness. With the computer on, one of the prongs put out some voltage. The only thing it could be that I can think of that it could be is the o2 sensor heater. So voltage is at least getting to the o2 sensor harness. How could I test to see if the ground is working? I am a complete dip when it comes to electronics, but I'm trying to learn.

And no, you didn't mess up my thread. I've been having terrible luck with this problem and have problably made about 20 threads on it alone, with no luck fixing it yet. But this is the closest I've came so far to tracking it down.

ponyboy302 · Dec 13, 2004

Here's the solution according to my electricians book. With the engine off connect the red lead of the metter to the oxygen sensor signal wire. Start the engine and allow it to reach a closed loop operation. Voltage for the O2 sensor whould be constantly changing. This is because the O2 senser goes rich lean rich lean. if the O2 sensor doesnt respong and the voltage stays at 450millivolts it probably needs replacing.

giddyup306 · Dec 13, 2004

leakyfaucet said:
How could I test to see if the ground is working? .

Do a voltage drop test. Put your voltmeter in parallel with the sensor ground comming from the o2 sensor and place the other end on the ground. It shouldn't be any more than like .1V.

ponyboy302 · Dec 13, 2004

Forgot rich exhaust is anything above 800 millivolts and anything below 200 millivolts is lean.

giddyup306 · Dec 13, 2004

Rich exhaust is anything over 450mv and lean is anything under 450mv. .45v is stoch. a/f mixture.

ponyboy302 · Dec 13, 2004

giddyup306 said:
Rich exhaust is anything over 450mv and lean is anything under 450mv. .45v is stoch. a/f mixture.

http://www.interro.com/techoxy.html

leakyfaucet · Dec 13, 2004

giddyup306 said:
Do a voltage drop test. Put your voltmeter in parallel with the sensor ground comming from the o2 sensor and place the other end on the ground. It shouldn't be any more than like .1V.

Sorry, I don't understand what you're saying. You have to be a little more specific with me, I'm a dip about electronics.

giddyup306 · Dec 13, 2004

http://www.parttrackers.com/library/1/24/27/

If it receives a sensor signal of less than about 450 mV, it recognizes a lean condition, and if it gets more than that amount of voltage, it registers a rich condition (it's one or the other, there's no in-between). Either way, it instantly corrects by adjusting the injection pulse width or feedback carb duty cycle.

68c3 · Dec 13, 2004

The way I understand it is the ideal is .450v this is where the comp would like to maintain. So if the computer reads less it will add fuel if it reads higher it will cut back on fuel that's why it fluctuates the comp is constantly trying to maintain 14.7/1 a/f ratio (.450v). A steady reading would indicate a bad sensor.

As far as the voltage drop is concerned you want to set your leads up at each end of your groud wire comming from the sensor to where the wire actualy grounds. (If you post a wiring diagram this would be much easier)

I hope that helps some.

68c3

leakyfaucet · Dec 13, 2004

So I set the voltmeter to resistance?

Michael Yount · Dec 13, 2004

No - you want to read voltage, not ohms.

leakyfaucet · Dec 13, 2004

So I want to put one prong of my meter on to the heater ground coming from the disconnected o2 sensor, and the other prong on where the little ring terminal actually grounds? And there should be voltage going through that????

Michael Yount · Dec 13, 2004

With the car running and fully up to temp, you should be able to probe two of the three wire connects and find a voltage somewhere in the range of 200-800 mV (milli-volts - .2V to .8V).

leakyfaucet · Dec 13, 2004

Today I pulled off my oxygen sensor harness. I'm going to try to make my own, just to eliminate it as a possible failure. I also pulled my oxygen sensors out. When I shake them they rattle. Does this mean they're toast?

Also, I found one prong on the main harness that goes to the oxygen sensor harness that puts out 5V. That's the only prong that puts out voltage at all. I assume that is the power for the heaters in the oxygen sensors. The wire in the oxygen sensor harness that connects to this prong is just a loop that reconnects to the main harness. I've included a picture to better explain this. There are a few more wires in the harnesses but I didn't include them since they don't relate to what I'm talking about.

I tested the ends of the oxygen sensor harness that connect directly to the oxygen sensors and they don't get that 5V. So something is wrong. There is no way that I can see for the oxygen sensors to receive that 5V because the wire just loops back into the main harness. The loop is definetly factory.

Anybody have any ideas?

jrichker · Dec 13, 2004

Try heating the O2 sensors with a propane torch and making your measurements. It should give you some voltage out within the 100-800 Millivolt range.

The O2 sensor heaters use switched 12 volts from the ignition switch. If you probed the O2 heater wire and got 5 volts, either you probed the wrong wire or someone crosswired things. There is no place in the O2 sensor circuit that should read 5 volts.

leakyfaucet · Dec 13, 2004

All I know is that the connector that plugs into the oxygen sensor harness only had one prong giving out voltage, and that was 5V DC. The heater signal is the only thing that should be putting out voltage, right? Well, that 5V DC only comes on with the ignition switched to ON, so I assume that's the heater signal.

Where does the heater signal come from, the computer? I want to track it down. It's a green wire with a yellow stripe. I'm about to just eliminate the connections and the harness and wire that 5V wire straight to the oxygen sensors.

But oxygen sensors aren't supposed to rattle when shaken, are they?

HISSIN50 · Dec 13, 2004

i am afraid to post on this thread anymore.

im not sure if JR linked you to these two yet (i dont know what year they are for - might be an earlier model than yours).

http://www.veryuseful.com/mustang/tech/engine/images/o2SensorTests.gif

http://www.veryuseful.com/mustang/tech/engine/images/mustangO2Harness.gif

good luck bud.

leakyfaucet · Dec 14, 2004

Yeah, I've seen those, thanks. They don't show the correct wire colors for my car. Probably a different year. I'm having the worst possible time with this.

Oxygen sensor voltage?

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