Fuel Pump/CANBus Problem
My GS died today. It refused to start after I parked it up for about 30 mins. There's no fuel coming from either injector.
It was recovered....yes on the back of a flat-bed recovery truck..........and taken to a friend's workshop.
I need some help with the diagnosis. Here's what I've found so far:
Ignition on, self check OK, ECU happy. Turns over on starter but no fuel pump.
Fuel pump is powered through a "Fuel Pump Driver Module" from the ECU and the CANBus controller (Why can't BMW just use a relay like every other fecker :bang.
Pump itself is OK.
Can't find any power or signal going to the Driver Module from ECU/CAN when disconnected.
With everything connected I can't (easily) get in to measure a signal, however I'm seeing something on the output from the DM to the pump. Not 12volts, but something.
I don't know how the CAN bus works but my initial guess is that the DM is powered +12V through the CAN controller, so that no CAN = no engine, and gets its power earth through the ECU for the same reason. It then gets a separate signal from the ECU - not the CAN - to run the pump as appropriate.
So.....initial diagnosis is....
The DM is dead (I'll come back to why in a minute) and so won't drive the pump. With no DM connected the CAN and/or ECU shuts the thing down anyway so I won't and shouldn't expect to see a signal from the CAN/ECU.
To confirm the diagnosis I really need to know the following:
1 - Should I be seeing 12V at the DM power input when it's not connected or will the ECU/CAN shut it down as I suspect?
2 - Should I be seeing a signal on the signal wire for the DM when not connected? If so what does it look like (I've never poked around a CANBus before). Am I going to have to get the oscilloscope out to find it?
3 - If I make the effort to break into the feed to the DM when its connected what will I see? I suspect I'll see a permanent 12V power feed and some kind of on/off signal from the ECU. Correct?
4 - Anyone seen this before?
5 - Is the DM available as a separate module?
Now, the problem with the Driver Module is.....
It lives in a wee housing on top of the fuel pump mounting flange. It's sealed off from the inside of the tank with a fancy connector and from the outside world with a rubber gasket. The gasket on this one was not installed properly and was poking out. As a result the inside of the housing was full of a mixture of fuel (presumably from inside the tank and/or spills while filling) and water. The fancy connector has been soaking in fuel for so long it was spongy instead of solid (managed to get it off without breaking it, just!) but more importantly the contacts were well corroded.
Theory at the moment is that the extra effort of pushing current through the corroded connectors has proven too much for the DM and it has expired. Sound plausible?
One final question – If I ditch the DM altogether and wire the fuel pump through a relay that only activates on starter cranking/engine running will the ECU and/or CAN bus controller throw a wobbly fit?
Hope someone can help.....
"A map is not the territory it represents, but if correct, it has a similar structure to the territory, which accounts for its usefulness".