Does anyone know what voltage our bank 1 (upstream pre cat) o2 sensors should read? I'm curious what they would read at idle and also when pressing/releasing the gas pedal. I'm trying to trouble shoot a CEL and I'm seeing voltage at my oxygen sensor but I don't know if it's correct or if it is responding to engine load correctly.

Any help would be appreciated,
Thanks,
-- Eric

 

sorry i can't help you with the voltage. what cel do you get? i get the increased emissions CEL because I think the o2 sensor might be damaged. are they expensive to replace?

 

If you load up INPA, it tells you what voltage should have been read and what is read by the computer. I am not very sure right now, but I believe it said the expected value should have been around 3.0v.

I got the CEL light myself and loaded up INPA. One of the two oxygen sensors reported 0.0v back which suggested a (possibly) broken circuit. But after deleting the error and restarting the car, the error did not reappear so it could have been intermittent.

I will retest over the weekend and update the thread if I discover anything new...

 

OK... Checked it once more: the actual voltage should be around 1,5V NOT 3 as a wrongly stated previously.

 

The voltage from the O2 sensors depends on the air/fuel ratio. It will be different depending on the AFR in any part of the RPM range.

With my last tune, that was a bit lean on E85, voltage started at 0.9V and droped to 0.8V at the 7300 RPM rev limmit in 2nd gear.

 

After reading a bit more and doing some more testing I learnt a lot of things

1. As **** stated, the voltage fluctuates according to the load.
2. The sensor needs to heat up to 350°C (600°F??) to give a reading, otherwise it is an "open-circuit".
3. The ECU pumps current through the sensor to test its functionality, so a constant current reading means the sensor is not functioning or the engine is off (but ignition ON).

Now specific to the R56, INPA reads a voltage of 1,5V for the PRE-CAT sensor and 0,45V for the POST-CAT sensor (engine off). I believe the first one is the type with heating element because the voltage fluctuates instantly when the engine is started (but readings do get greater fluctuation as the engine warms up). The latter takes minutes before the voltage fluctuates at all.

Maximum values are 2V for the first sensor and 1V for the second.

PS: The Direct-Injection Cooper S has a 5-wire sensor which is more expensive than the one of the simpler Justa...