F355 slow down light - how to diagnose fault?

[BMW A6]

F355 5.2 Motronic; the cats are cold, as engine just started, yet the Slow Down Light (SDL) is permanently on and 1 cylinder back is shut down.

I have removed the 2 connectors into the cat ECU (I think 1 is the thermocouple and the other the 02 sensor?), and yet the SDL remains on.
Picture shows the left hand side module, but I have also disconnected the right hand side too.



Why is cat ECU still sending signal to shut down a cylinder bank when the 2 connectors into the cat ECU are disconnected?

Are there connections from the cat ECUs to another ECU, which is forcing 1 bank to shut down? If so, where are those?

Really don't know what to try to see what is faulty and on which bank?

[BMW A6]

Thank you Larry.
I was under impression that only cat ECUs would cause SDL?
Are you saying that it could also originate from faults in ignition system?

I will have to try and convert the 3 pin OBD plug into the 16 pin system, I guess?

[BMW A6]

Thank you all for input.

I am still not sure what connects the cat ECUs to the motronic - is there a cable I can follow?
I think I can see the 02 sensor (2. in pic below) and thermocouple (1. in pic below) connecting into each cat ECU, but how does the ECU connect to next item to initiate cylinder bank shutdown?



Also, the 2 panels behind the seats do not have the standard 16 pin OBD port - they both are 3 pin. Are they both diagnostic ports doing the same thing?

Is there something I can purchase to plug into the car to reveal the faults? I have a 16-pin OBD tool which bluetooths car data nicely to my mobile phone on my other modern cars..........would be useful to do the same for the 1996 Ferrari.

[BMW A6]

I've purchased a 3 pin to 16 pin OBD adaptor. Will plug it in to the connector behind the seats and see what it throws up.

[BMW A6]

phib said:

BMW A6 said:

I've purchased a 3 pin to 16 pin OBD adaptor. Will plug it in to the connector behind the seats and see what it throws up.

Did you manage to get the three pin to work ?

Thanks Phib

The 3 pin adaptor did not slot into the cable behind the seats.

I will next try to whip out the ECUs and thermocouples and take it to someone to test.

Not sure when though. Car is SORN. And I am in lockdown.