Re: Can the ECU detect aging O2 Sensor - Saab NG900 & OG9-3 Bulletin Board - Saabnet.com
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Re: Can the ECU detect aging O2 Sensor
Posted by Dean (more from Dean) on Sun, 6 Oct 2002 18:02:31
In Reply to: Can the ECU detect aging O2 Sensor, Makis, Sun, 6 Oct 2002 16:10:43
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If you use a low impedance voltmeter, the extremely low current signal from the 02 signal will be lost.
The ECU from 96+ has ODB-II diagnostics and should sense a shorted or open circuit. If the ECU cannot get the O2 sensor voltage into range buy changing the fuel mixture, the ECU will do a CEL for an adaption fault. An adaption fault can occur when the 02 signals are good, but the injector duty cycles are out of bounds compared to mapping. The point of this is that the ECU can flag a problem where the mixure will be wrong in the future for higher thottle postions, as the current duty cycle ratios will not allow for fuel mixture demands when higher fueling rates are required.
I used to test the 02 sensor voltage on a '78 Volvo V6. I could check for the signal, and could stick a 1.5 volt battery on the ECU side and know that that side was responding as it would run things rich in response and the idle would be significantly affected. In your case, with a lack of a O2 sensor signal, the ECU may have gone into a default run rich mode, waiting for the signal. After a time out period of running and noting that the engine temperature had been reached for a period of time, it could then have thrown the CEL, having given up on waiting for a signal. But with ODB-II, I would expect a faster response, but that is only my expectation.
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