without an Alfa
Join Date: Dec 2011
Location: United Kingdom
That is the problem with trying to diagnose a CAN fault with a multimeter, it only gives you an average voltage.
I am not sure what you are saying. You actually disconnnected the ABS CAN lines and read the voltages on the ECU end and got 0v on both lines?
If so, which is the other line that is reading 2.5v?
when the CAN line is busy (sending lots of messages) then the average voltage will move further towards 2.5v on the high and low lines than when it is not busy.
2 things could be happening here.
1.reading 0v, 0v;
the ECU is recognising that you have disconnected the CAN lines and crashed or stopped transmitting (probably logging an error) the ABS unit doesn't notice and continues to send the same information.
2. reading 2.4~2.6v
because the ECU is not receiving any signal from the ABS unit it has ramped up the number of requests for information resulting in a different average voltage.