Re: O2 Sensor

[ti@amb.org (Ti Kan)]

Aleksander Mierzwa writes:
> At 22:04 99-09-12 EDT, Christopher Gharibo wrote:
> >I have a '91 CQ with 57k miles on the odometer.
> >I noticed that it doesnt have a O2 sensor light.  How do I know this thing
> >needs replacement?
> 
> You don't. O2 sensor light, if present, is simply triggered by the odometer
> and is supposed to come on at certain mileage, usually 40K miles for
> non-heated and 60K miles for heated sensors. It doesn't say anything about
> actual condition of the sensor. On a healthy engine heated sensors tend to
> last much more than 60K miles.

Also, on the newer cars with digital ECUs (your CQ should be one of these)
a malfunctioning O2 sensor should cause a fault to be recorded, and can
be displayed by dumping the codes.  That said, O2 sensors sometimes
fail gradually by becoming slow to respond.  That may not register as
a fault on the ECU but would hurt performance and mileage anyway.  The only
good way to test it is to put an oscilloscope on it and watch the output...

-Ti
96 A4 2.8 quattro
84 5000S 2.1 turbo
80 4000 2.0
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    ///  Ti Kan                Vorsprung durch Technik
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