Can Bus Voltage

The Bus voltage comes from the modules that are connected on the Bus. For instance, the PCM generates the CAN Hi and CAN Lo. You can connect a PCM directly to a labscope and see the voltages regardless of anything else on the network. The CAN microprocessor gets it's voltage usually from a 5 VDC or 3.3 VDC regulator on the mainbord of the PCM. If CAN is shorted to ground or power on both Hi and…

So if voltage is 2.4 and you should 4.5 hi and low and can communicate with all other modules except ecm . No what

o and new ecm

You can disconnect ECM and see if the voltages come up. You should also be able to backprobe the wires at the ECU and make sure both Lo and Hi are present.

already did that

So voltages are not changing with ECU disconnected? There is signal getting to the ECU? Would you want to try to communicate with ECU on the bench? Drop me an email with a picture of ECU and I will try to find a connection diagram. …

I can disconnect 94 pin connector at ecm wait two minutes and plug back in and car will start and run with no codes

Does the vehicle stall after running or just not restart?

Runs just fine tell you cycle key

Wow you got a challenge on this one. It seems that if it were a CAN issue there would be codes for lost communication with ECU. Relays? Drag test terminals to ECU?

There is codes for lost comm with ecm . And I did do drag teat

The Wiring diagram shows a splice pack on the left and one on the right. My diagram does not say exactly where. If you can locate the splice packs then your could eliminate modules one by one that could be effecting the bus.

Found them already did that

Im going to retry tomorrow but pack probed in to gate way . Im thinking gate way iss

Michael is right. voltage is generated from all of the modules on the network. If you are not seeing voltage then there is some bringing it down. Something on the physical level. Mike

Did you do the ol' ohm test for the terminating resistors? (I know German vehicles dont always have the same 60 ohm values as other vehicles,but your service info should provide what you are looking for as far as that goes)

yep

And?

all good