Saab 4-cyl gets 2 >> - Saab NG900 & OG9-3 Bulletin Board - Saabnet.com
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Saab 4-cyl gets 2 >>
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Posted by damien [Email] (more from damien) on Mon, 30 Aug 2004 13:50:21 Share Post by Email
In Reply to: Oxygen Sensors, Marc Orloff, Mon, 30 Aug 2004 13:11:51
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The sensors are identical.

The first one reads the exhaust right out of the turbo, before the catalytic convertor. This has a sine-wave signal to the Trionic computer - like down/up/down/up/down... from
about .1V to .8V. This indicates lean/rich/lean/rich/lean mixture, bouncing around the ideal stoichometric air:fuel ration of 14.7:1. This is one of the main feedback loops for the computer to trim the fuel injector opening time.

The second O2 sensor is mounted after the catalytic convertor, and it usually reads flatline - I forget the voltage, but say .1V. The difference in the two sensor readings is due to the catalytic convertor, which is "cleaning" the mixture and burning up the tiny portion of unburnt fuel.

When the second sensor reading starts matching the first (sine wave), you know that the catalytic convertor is dead. You can see this easily when you plug in a Tech-2 device and read the sensor directly through the Trionic computer. Diagnosing the cat is the ONLY function of the second O2 sensor, implemented by Saab in 1995-1996 per Federal OBD-II regulations (on-board diagnostics - 2nd revision).

posted by 63.207.93...

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