No signal ground from ECM for right front O2 sensor signal ground..
2003 Disco 2 with 2000 8 cyl engine.
I have good lead traced back to and thru socket of 24 pin plug (pin 10). But, it appears that the signal ground isn't being provided from ECM. Pin 9 provides signal ground for left front sensor as expected.
Any work arounds without replacing ECM?

 

Not sure of what you are saying based on your terminology. The oxygen sensor creates a voltage, the ECU just reads it. I have had the oxygen sensor "drivers" as they are called in the ECU go bad, only recourse was to replace the ECU. I only was able to verify this by swapping ECU's between otherwise fully functional trucks.

 

The ECM provides 4 distinct/seperate O2 sensor signal grounds thru pins 8, 9, 10 and 11 of the 24 pin connector. Unfortunatly my ECM is malfunctioning and Pin 10 is open (does not pass ground). Pins 8, 9 and 11 function as they should. Looking for work around to get signal ground back onto pin 10 again. Not sure if inside the ECM there might be a common amongst these signal grounds. If that's so it might be ok to combine wire for pin 10 with wire for pin 9 to get function back to signal input on pin 16 (Pre-cat sensor right side Input). Assume this bridge should be made as close to connector as practical to keep things as close to spec as possible (share load, capacitance, resistance etc).
Anyone know for sure? Suggestions?

 

I say go for it! What's the worst that could happen?

 

That's what I thinking too. I might add a diode just past the bridge to each wire in case there is a slight feedback voltage that could influence the alternate signal circuit's signal levels.
Probably overthinking this. The diode is likely the only internal component of the ECM separating the 4 ground pins. Just a theory.

 

Why not just drop in a replacement ECM?

 

"Dropping in" a replacement ECM doesn't seem as easy as it sounds. Probably have to do the entire suite. Dealers are either reluctant or just refusing to flash ECMs nowadays if that needed. I will likely crack open this ECM, bypass the short and add a diode externally for this line.

 

Sort of "Went for it."
Decided to test effect on an alternate line signal ground while waiting for diodes. I decided to tie on with signal ground for right rear(post cat) since that is less critical to engine performance. As I expected, the graph for my right front O2 sensor signal is now in spec and the rear sensor signal is still functional though a bit less varying. I will add the diodes when they arrive and take another look. The diodes may not work or improve signals but if things are at least equivocal I will leave them in just for peace of mind.
Either way, I will report my results.

 

Maybe use a meter to check for internal diodes between the 4 ground terminals. I suspect you won't find diodes there. If you get 0.5 V drop across an external diode, that may take the signal out of range, or bias the signal rich or lean.

 

Good points to consider. I did expect to and did see a slight effect on the rear sensor caused by the influence of the wider voltage variance being produced by the front sensor when the two grounds were combined. Remembering this is the sensor ground that is being "fooled with" but because we are dealing with such small voltages and changes any off-kilter arrangement is bound to have some effect. I'm hoping the diodes, if chosen and placed correctly, can mitigate that effect. I'm not sure I would expect to see diodes between the signal grounds within the ECM but rather between the individual signal ground traces and the battery ground trace within the ECM. This, of course, is just conjecture on my part.. Thanks for the ideas.