Secondary O2 sensors - what does the ECU want to see?

[e90n52b30]

Pokey I'm not sure if you're still looking for some data on the O2 sensors but here's some data from my 330xi, n52b30, msv70. This screenshot was taken at idle with the engine at operating temps.

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The pre cat sensors were around 2v while cruising. They jumped to around 3v when letting off the throttle, and dipped just under 2v while accelerating.

At idle, the pre cat sensors stayed around 2v.

The post cat sensors stayed arounf 0.6v. They didn't fluctuate much while under load or at idle, accel, decel etc. They did however drop to 0v periodically but it was random. I noticed it happened more when approaching a full stop. I'm not sure if this normal operation or a lag in the communication between my car and the laptop.

[ajm8127]

The primary sensors are wide band sensors, so they will output a voltage proportional to the air fuel ratio. I would guess 2 volts is somewhere are 14.7 or so (lambda = 1 for gasoline). From your description, the voltage is directly proportional to the ARF or the lambda value as it increases under lean conditions (deceleration, lambda > 1) and decreases under richer conditions (acceleration, lambda < 1)

The secondary sensors are narrow band sensors and will read from about 0.2 to 0.8 volts, with the former indicating lean and the later indicating rich. These sensors will read about half a volt at stoich. When approaching a stop, the engine is running lean, causing the narrow band voltage to fall.

I doubt you would be able to get much useful information from INPA about the sensors. You'd need to hook something a lot faster up to the output of the sensors to really see anything interesting. This is where an oscilloscope comes in.

[e90n52b30]

Well I realized I had my dp fix connected to the wrong sensor. I had it connected to the one that failed it was still throwing an ses light. I swapped it to the good sensor and its now reading about .7v at idle. I noticied it will fluctuate around there most of the time but On decel, the value will drop to 0v, especially when coming to a full stop. The value always went to 0v at a full stop. The values were displaying pretty quickly with the other cable I have. I agree an oscilloscope would yield more accurate results.

As for the pin out on the DME, it was the same for n54. I verified that with my Bentley manual. So this should also work on the z4s, granted you find the correct pin out for the DME.

[e90n52b30]

Ohh and DME shows a ready state