ECU pin assignments for O2 sensor

[1 Thump]

Is this board awesome or what ?

[gremlin]

And on the lower left: a diode?  Why doesn't the other end connect to anything?  The ECU pin is labeled "SG"...  ??

That circuit is the sensor ground circuit.

It's main function is to provide a common reference for reading the sensor(s) output voltage(s)/current(s)

The actual frame ground of a vehicle is noisy as hell, this circuit acts as a quiet local ground field that collects all the sensors and brings them to the ECU, before connecting them to the chassis.

[singhg5]

In the previous photo of ECU circuit, the inverted triangle looked like an electrical symbol for a diode and I had penciled as such. 

Thanks to JVS and Gremlin who corrected that to be 'Surface Sensor Ground Circuit' - though I do not fully understand that thing.

Below is the revised version of the ECU circuit - hopefully the labelling is more readable and correct.
 
Surface ground should read SENSOR ground in the diagram, prepared by my tired brain at midnight on the topic I know little  . 

[gremlin]

SENSOR ground  (aka sensor return) or signal ground.

[singhg5]

SENSOR ground  (aka sensor return) or signal ground.

'Sensor Ground' it is Now ! In its 3rd revision  .

While we are at this topic,  can you explain a bit more. 

If the 'sensor ground' wire is not attached to frame, where is it attached ? Is it the ECU pin 24 that act as 'sensor ground' ? If so, how does it act as ground ?

Also, it seems that 4 sensors - throttle position sensor, air manifold pressure sensor, engine temperature sensor and O2 sensor - are part of this 'sensor ground circuit'. 

How does this grounding provide common reference for sensor output and perhaps reduce background electrical 'noise' or variation from sensor to sensor for more accurate reading ?
 

[gremlin]

First, let me preface this discussion by saying that I KNOW NOTHING specific to the bullet.  The knowledge I am drawing on for this discussion is standard engineering school fodder.

:Having said that:

The signal ground is connect to the frame ground, however, that connection is via a relatively high inductance path.  - Imagine how Lake Superior is connected to the Atlantic Ocean......   generally speaking, the surface disturbances of the Ocean do not find their way up the chain to Lake Superior - However - they are interconnected !

[GreenMachine]

Gremlin: As u r aware, the best ground potential is earth and in some cases that requires a bit of engineering, chemicals, using a megger, etc to reach a given potential to satisfy the  requirement needed. Grounds are a antenna and radiate if the end point isn't tied to a lesser potential (chassis) . .I would think a standard motorcycle or auto has a bit of noise when viewing the Grounding with a anaylzer...Either way, it's the standard that's been in play for quite a while. It works, cost effective and fairly easy to fix.    Excessive vibration doesn't help our cause.
..I did enjoy your analogy by the way..GM