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Thread: Question about O2 Sensor Reference Voltage

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2016-04-25 22:28:15
Question about O2 Sensor Reference Voltage
So I'm a complete noob at this, but I just installed my Nismotronic and started driving a bit while recording logs.

Yesterday I did a short drive around the block while the ecu was sort of dangling into the passenger side footwell.

That log shows the O2 voltage fluctuating as I would have expected, and the AFR according to the fluctuations.

Today, I secured the ECU back in place, did some more logging, but the entire time, the voltage stayed at 2.6v, indicating an AFR of 15.2.

This stayed a flat line regardless of idling, accelerating, coasting, etc.

My basic research tells me that 2.6v is the "reference voltage" for some O2 sensors.

The question: Does that voltage come from a sensor that's in some state of failure, or does it come from the ECU as a stand-in for a missing O2 sensor?

I'd like to know if these symptoms are more indicative of a malfunctioning sensor, or possibly a loose connector.
2016-04-26 09:52:36
Are you using the ADC signal box yes?

Remember that if you have a loose signal, ADC channels can accidentally interpret voltage coming from inputs nearby. Example, my Wideband sensor signal broke loose, and Nismotronic locked on solid 12.0AFR. This was due to the flex fuel content signal, being accidentally snapped up by the flexsignal, now that the channel was empty. (Locked at 2V-ish)

Other possibility is a bad wideband sensor. Do you have a gauge connected?
2016-04-26 11:58:40
I actually don't have a wideband installed yet. I'm only using the stock O2 sensor at this point.
2016-04-26 13:30:22

Stock o2 sensor is a narrowband sensor. It will only output high/low voltage. It cannot be used to monitor AFR at all. It is only used for closed loop operation, to switch the mixture between rich/lean, letting the 3-way catalytic converter do its job.

Warm the engine up, and look at the "NB lean flag", there is a checbox next to it. It should pendle between on and off. Do not look at the AFR value, that will only be accurate once you install a wideband

Also, the ECU will ignore the stock 02 sensor until certain conditions.
MIN ECT WARM START - Minimum warm start ECT for closed loop.
MIN ECT COLD START - Minimum cold start ECT for closed loop.
WARM START ECT - Minimum ECT at startup for warm start.
MAX RPM - Closed loop is disabled above this RPM.
MAX MAF LOAD - Closed loop is disabled above this MAF Load.
MAX MAP LOAD - Closed loop is disabled above this MAP Load.

So make sure that you have enough heat, and are not loading the engine too much.
Last edited by Dala on 2016-04-26 at 13-33-57.
2016-04-26 14:00:43
This is very helpful. Thank you.
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