PCM Question

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Oct 1, 2003 | 05:15 AM

maxi-freak

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PCM Question

Doe's the PCM pulse BOTH of our upstream O2 sensors?
I just read that the 3 way catalyst effeciency is monitored by the ratio of upstream O2 frequency to downstream O2 frequency.

I have set a PO420 and one of my bank's upstream sensor is pretty much DC and doing NO cycling at all. The other upstream is cycling from .1 to .8V, which is good.

Oct 1, 2003 | 05:20 AM

UMD_MaxSE

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both upstream sensors should be pulsing...

Oct 1, 2003 | 06:09 AM

maxi-freak

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Ok...well that tells me that I need to do some back tracking to the PCM as to why there is no pulse. I might need a service manual unless someone can tell me which pin that it's on at the PCM.

Oct 1, 2003 | 06:16 AM

UMD_MaxSE

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Pins 62 and 63 on the ECM are the front O2 sensors... The O2 sensors send a pulse to the ECM... the ECM just reads the voltage level from the O2 sensors...

Oct 1, 2003 | 06:24 AM

maxi-freak

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Really? So the O2 sensors have a built in oscillator?

Oct 1, 2003 | 06:31 AM

UMD_MaxSE

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Quote:

Originally Posted by maxi-freak

Really? So the O2 sensors have a built in oscillator?

they are not electronic oscillators...

Quote:

The front heated oxygen sensor is placed into the front tube. It detects the amount of oxygen in the exhaust gas compared to the outside air. The front heated oxygen sensor has a closed-end tube made of ceramic zirconia. The zirconia generates voltage from approximately 1V in richer conditions to 0V in leaner conditions. The front heated oxygen sensor signal is sent to the ECM. The ECM adjusts the injection pulse duration to achieve the ideal airfuel ratio. The ideal air-fuel ratio occurs near the radical change from 1V to 0V.

Oct 1, 2003 | 07:05 AM

maxi-freak

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Ok...that makes sense. Thanks UMD_~! So really the cycling voltage is due to the feedback loop that occurs.

Oct 1, 2003 | 07:15 AM

UMD_MaxSE

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Quote:

Originally Posted by maxi-freak

Ok...that makes sense. Thanks UMD_~! So really the cycling voltage is due to the feedback loop that occurs.

the voltage cycling is caused by the control loop formed by the engine adjusting the fuel ratio based on the voltage read from the sensor. When the sensor outputs a low voltage or high voltage, the ECM adjusts the fuel injector pulse width to correct the rich or lean condition. The point at which the sensor switches represents the ideal A/F ratio...

Oct 1, 2003 | 07:42 AM

maxi-freak

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So it sounds like my upstream sensor on bank 1 has gone bad. I just can't help but wonder why there's not another code being set - that pertains to a bad sensor ....or even any of the PO13* type codes.