O2 sensor output
01-14-2002, 08:27 PM
#1
Burning Brakes
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O2 sensor output
Can anyone tell me where the test point is that I can connect my DVOM and read the O2 sensor voltage? I see there is a three wire diagnostic plug on a bracket at the rear of the cam carrier, and as I recall Bosch made a diagnostic tool which used it for a number of readings. I've replaced the sensor due to a high CO failure of my emissions test, and I can read it by disconnecting it and going from the black wire to ground, but I want to see it changing so I'll know the feedback system is working before I go back for my retest. It's an 85.5 NA. Thanks.
01-15-2002, 07:38 AM
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Dear Mark,
This is a 1985.5 944. There is no diagnostic plug or test point. All you can do is do what you have done. The output should be between 150-900mv. If you have somebody rev the 944 whilst you are reading the output you should see this change as the oxygen content in the exhaust changes.
Ensure the engine is at operating temperature or hotter. Little clue for emissions tests by the way. The O2 sensor only works when it is at 600F or above. Get her really hot before testing.
You could make up a break out lead I guess.
I do not know what you mean by feedback but the O2 sensor is just a like battery. One way only, into a rather crude DME set up.
Ciao,
Adrian
911C4 (and a 1985.5 944)
This is a 1985.5 944. There is no diagnostic plug or test point. All you can do is do what you have done. The output should be between 150-900mv. If you have somebody rev the 944 whilst you are reading the output you should see this change as the oxygen content in the exhaust changes.
Ensure the engine is at operating temperature or hotter. Little clue for emissions tests by the way. The O2 sensor only works when it is at 600F or above. Get her really hot before testing.
You could make up a break out lead I guess.
I do not know what you mean by feedback but the O2 sensor is just a like battery. One way only, into a rather crude DME set up.
Ciao,
Adrian
911C4 (and a 1985.5 944)
01-15-2002, 06:28 PM
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Burning Brakes
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Adrian; Thanks for the input. I thought last night about adding a breakout plug, it wouldn't be difficult, but I feel certain that some means has been provided to look at the live O2 signal as it's a vital diagnostic tool. As it is all I can see is the effect of having no O2 signal at all, because I have to disconnect it to get my reading. The old sensor hovered in the .12v to .15v range, which was telling the computer it was lean. the new one goes .8v+, so I'm sure it's responding. If I had a live signal I could see if it varies which would show me that it was giving the 'puter a good signal, and the 'puter was adjusting the mixture accordingly (closed loop). If I could see that, I would be certain that my tailpipe emissions were good. I'm gonna see if I can pick a few brains locally before I add a breakout wire. Mark P.
