O2 sensor question

[MLCMK]

Hi all

 

I have a question on how close the voltage values for Bank 1 position 1 and Bank 2 position 1 should be when the car is warmed up and running.

 

I had the cruse control set for 60 mph and took the snapshot below of the readings and noticed the Bank 1 voltage was significantly lower than the Bank 2 number

 

 

From what I understand the low voltage will make the ecu think that bank 1 is running lean and make it over compensate with extra fuel

 

Am I on the right track or miles off?

 

 

Sent from my iPad using Tapatalk

[karlh]

Are you sure you're measuring the voltage of the air-fuel sensor located before the cats? Those are wide-band sensors, and output a voltage of approximately 1.5 volts at lambda = 1. The voltages you show look like a narrow-band sensor, the kind located after cat 1.

[Tricky-Ricky]

O2 sensor 1 of bank 1 and 2 are used by the ECU to monitor for the correct air fuel mix, whereas sensors 2 of bank 1 and 2 are the cat monitors, and use a much reduced signal variation and cycle, and in normal circumstances not used to monitor fuel mix, and so will show a completely different reading to sensors 1.

 

 

However on looking at your gauges again it would seem that it is reading sensors 1, a so it would seem that one sensor is reading low, which would indeed prompt the ECU to add more fuel,

Does that reading change much at various RPM/load? if not then that a fair indication that the sensor is dead.

Edited April 17, 2016 by Tricky-Ricky

[MLCMK]

Are you sure you're measuring the voltage of the air-fuel sensor located before the cats? Those are wide-band sensors, and output a voltage of approximately 1.5 volts at lambda = 1. The voltages you show look like a narrow-band sensor, the kind located after cat 1.

 

Hi Karlh, I just double checked and these readings are from the sensors before the cat (I looked at the PIDs)

 

[MLCMK]

O2 sensor 1 of bank 1 and 2 are used by the ECU to monitor for the correct air fuel mix, whereas sensors 2 of bank 1 and 2 are the cat monitors, and use a much reduced signal variation and cycle, and in normal circumstances not used to monitor fuel mix, and so will show a completely different reading to sensors 1.

 

 

However on looking at your gauges again it would seem that it is reading sensors 1, a so it would seem that one sensor is reading low, which would indeed prompt the ECU to add more fuel,

Does that reading change much at various RPM/load? if not then that a fair indication that the sensor is dead.

 

Thanks Tricky-Ricky, below is a snapshot from a bit later in the run, decreased revs and speed. There is some fluctuation on both sensors but the blue bank 1 sensor always reads lower than the yellow bank 2 Voltage

 

Voltage switching is clearer to see in the below

Edited April 17, 2016 by MLCMK

[Tricky-Ricky]

There is always is a difference between O2 readings from one bank to the other, and now I have seen that the sensors are cycling as they should, I would say that now looks OK to me, similar to some of the logs I have taken from the std ECU.

But its worth keeping an eye, as it could be a lazy sensor or on its way out, but I wouldn't worry too much for now, it will throw a CEL should the sensor go down.

Edited April 17, 2016 by Tricky-Ricky

[MLCMK]

There is always is a difference between O2 readings from one bank to the other, and now I have seen that the sensors are cycling as they should, I would say that now looks OK to me, similar to some of the logs I have taken from the std ECU.

But its worth keeping an eye, as it could be a lazy sensor or on its way out, but I wouldn't worry too much for now, it will throw a CEL should the sensor go down.

 

Excellent, thanks for your help Tricky-Ricky. I will keep a eye on it

[Sam Mcgoo]

That is normal on the 350. For some reason Bank 1 sensor voltage is always about about 50% of bank 2.

When fault finding, I found it easier to look at the Bank 1 vs Bank 2 Fuel trims. This will show you if one bank is running richer/leaner than the other and trying to compensate.

[MLCMK]

That is normal on the 350. For some reason Bank 1 sensor voltage is always about about 50% of bank 2.

When fault finding, I found it easier to look at the Bank 1 vs Bank 2 Fuel trims. This will show you if one bank is running richer/leaner than the other and trying to compensate.

 

Thanks Sam

 

I'll build a dashboard to check the fuel trims and add it into dash command

 

Cheers

 

Jason

[karlh]

Are you sure you're measuring the voltage of the air-fuel sensor located before the cats? Those are wide-band sensors, and output a voltage of approximately 1.5 volts at lambda = 1. The voltages you show look like a narrow-band sensor, the kind located after cat 1.

 

Hi Karlh, I just double checked and these readings are from the sensors before the cat (I looked at the PIDs)

 

 

After reading your reply I obtained a scan tool and checked my 2005 Z. I got the same readings that you did; approximately 0.3 V for bank 1 and 0.6 V for bank 2. It appears that Nissan is using PID $1B to report these values. PID $1B is designed for older, narrow-band O2 sensors, and reports voltages between 0 V and 1.275 V. The pre-cat sensors in our cars are wide-band, and output approximately 1.5 V at lambda = 1. If our readings are the true values then both banks, and especially bank 1, are running very rich. I suspect Nissan has scaled the wide-band readings to fit within the narrow-band range and that 0.3 V and 0.6 V represent lambda = 1 for banks 1 and 2 respectively. Unfortunately, I cannot find anything in the Service Manual to confirm this.

[MLCMK]

Are you sure you're measuring the voltage of the air-fuel sensor located before the cats? Those are wide-band sensors, and output a voltage of approximately 1.5 volts at lambda = 1. The voltages you show look like a narrow-band sensor, the kind located after cat 1.

 

Hi Karlh, I just double checked and these readings are from the sensors before the cat (I looked at the PIDs)

 

 

After reading your reply I obtained a scan tool and checked my 2005 Z. I got the same readings that you did; approximately 0.3 V for bank 1 and 0.6 V for bank 2. It appears that Nissan is using PID $1B to report these values. PID $1B is designed for older, narrow-band O2 sensors, and reports voltages between 0 V and 1.275 V. The pre-cat sensors in our cars are wide-band, and output approximately 1.5 V at lambda = 1. If our readings are the true values then both banks, and especially bank 1, are running very rich. I suspect Nissan has scaled the wide-band readings to fit within the narrow-band range and that 0.3 V and 0.6 V represent lambda = 1 for banks 1 and 2 respectively. Unfortunately, I cannot find anything in the Service Manual to confirm this.

 

Thanks for confirming you see the same readings as I do, I'm keeping an eye on mine now on a regular basis .

 

Something I found about mine recently is that it is a decat (didn't think to check that when I bought the car!), just thought the sound was normal for a cobra system. You live and learn.

 

I think you are right with the Nissan scaling, it's too much of a coincidence that both cars have identical readings.

 

Cheers

 

Jason

 

 

[Tricky-Ricky]

Pretty sure that the lambda sensors on the Z are 2v wide-bands rather than 5v, that why you end up with an odd reading on some loggers/diagnostic machines and dashboard apps, but the higher reading on one back is normal.