[cjalaff]

What started as a code here and a code there, which I would replace parts and reset thinking it would go away, pretty soon I stacked up to a long list of random codes that would come and go.

Misfires, VANOS, O2 sensors and others, but only what I could see via MHD. When I connected ISTA there were a dozen of codes “not able to communicate with DME, CAS, bla, bla bla, and when I cleared most did not come back. When I ran a test with ISTA, the following would show:

GS19D S 0364 No communication possible with: Transmission control unit unknown S 0180 No communication possible with: Safety module/restraint system
CAS S 0074 No communication possible with: Car Access System
KOMB87S 0119 No communication possible with: Instrument panel

Every time I re-ran ISTA different codes would show and others would disappear.

So I started to trace wires and run tests based on the ISTA recommendation, however; every value was good, no burnt fuses I was getting correct voltage for the test pins indicated. I even validated CAN HI and LOW value was correct.

I then started to drill into ISTA. I would call each ECU function showing errors, and I would get random responses, from “No response from the ECU” to “partial response from the ECU” and eventually “ECU is responding normally”. WEIRD RIGHT?

Well as I went into diagnosis mode and, for example selected voltage, it would show 12v then flip over to “unknown”, then back to 12v then to “unknown” every second. I then read the low pressure pump and it would show a BAR value but would flip flop from a number to unknown back to a number every second. This was the same for all devices on the CAN. I don't think I saw this behavior in the DME, but I only checked the voltage and it was holding steady and not flipping.

What could be causing the devices on the CAN network to be flipping from a value to "unknown"?

I am so close to figuring this out I can smell it. Any Ideas?

[cjalaff]

Issue resolved. It was related to the Com Port setting in the PC running ISTA.
Lower the timeout and latency on the USB cable to 1 and all modules are now green with no communication errors.
https://www.bimmerfest.com/threads/m...olved.1107425/