2004 BMW 330i E46 No start No Communication

I received a call from a friend early in the week about a no start, no communication issue he was having. The offending vehicle was a 2004 BMW 330i. He stated the vehicle would start and run fine cold. Once it reached operating temperature, the temp gauge would go to hot and it would no start, (no crank condition). I informed him that when the instrument cluster loses comminucation to the DME the temp gauge defaults to full hot. As it gets it temperature information via the CAN-bus from the DME. Another good way to check if an ECM from almost any manufacturer is online is the MIL. In this case it was not.

The MIL is regulated to be on when the key is on and engine is off.

I pointed him in the correct direction and he was off to perform some tests. Once he got back to me everything was pointing at a faulty DME. Even though he is an experienced BMW mechanic he was second guessing himself. Asking me if I really thought he was on the right course. Reviewing his tests with me over and over again. He had that feeling in the pit of your stomach, the one you get right before you tell your boss the vehicle needs a $1000 part.. not including the labor to install or program.

Two days later my phone rang the caller ID showed it was the shop with the 330i. He had bad news, (as he put it).

I put in the new DME, it still won’t communicate with my scan tool and now it NEVER starts.

We spoke a few minutes more and I decided I had to get up there and look at the car myself. If you recall the original problem was the vehicle would start cold and stall once hot with no restart. Things are worse with the new DME.

The next night I drove north to Concord, NH to see what was going on with this 330i.

A short revealed the DME was now communicating. I always try with the factory scan tool, then with a generic OBD II scan tool.

One step further revealed a list of faults pointing to the DME.

When diagnosing bus faults it is important to identify the communication status of each module on the bus. A bus-system wiring diagram may be needed to verify all the modules involved.

The next step is to review fault codes stored, (if any) in each module. You want to write them down and see which module is being reported as not communicating by the most modules.

I now had my plan of attack and it was time to open up the diagnostic case. I hooked my pc-based scope. I am currently using the ATS limited. It is a small, powerful, 4 channel pc-based scope.

I gained access to the DME, which was easy as it was just replaced.

While attempting communication I would monitor the K-bus. The signal that was present was acceptable.

Moving to the CAN-bus next to confirm the signal there was acceptable. It was.

The CAN-bus does look quiet here. That is because during koeo all you will see is status messages. If the DME was online it would be much busier.

My tests confirm our earlier diagnosis via the telephone. I advised the shop to get another new DME. They were a bit worried because this was a new unit from BMW. I asked them to notify me when the new part would arrive.

I was back in the shop two days later, here is what I saw.

New DME installed, (not yet programmed).

Temperature gauge is is correct position. Indicating DME is online.

K-bus with DME online

CAN-bus with DME online. Much more traffic.

The second new DME fixed the problem.