In my December column, I mentioned that I did not have the energy to write about a really difficult BMW problem. I mustered the energy to discuss it this time around.
The problem car: a 2000 BMW 323i. The owner told us that it was cutting out badly while driving and the check-engine light remained on.
After connecting the car to the Integrated Service Technical Application (ISTA), we pulled two diagnostic codes related to the Digital Motor Electronics (DME). The codes that came up: DME A9 (engine throttle output stage shut off after diagnostic engine throttle output stage diagnostic fault) and DME 64 (control modules self-test signal not plausible). So we ran the test plans, but nothing came back bad.
We then tried to activate the throttle from the ISTA, but it would not operate from direct control. This was odd; if the throttle was bad, it should have failed the test. We then tested the wire harness from the throttle body to the DME. The connectors and the wires tested OK. Because the throttle wasn’t responding from the ISTA, we replaced that first.
After that, we ran adaptation and alignments. In the control area network (CAN), the modules and components need to see each other. The last step after the repair is to align the modules. We tried to align the DME with the other modules, but the DME kept kicking out of the operation. If we are unable to align the DME properly, the car’s powertrain won’t work correctly.
Back to basics
I then remembered this car has a bad Dynamic Stability Control (DSC) module. For years, my customer declined to fix this module because it’s expensive and he rarely drives the car aggressively. We then thought the DSC module might be pulling down the CAN alignment procedure.
We checked battery voltage and noticed that it was low (9.3 volts). We then checked to see if the alternator was charging and if there were any parasitic draws. The alternator was at 14.3 volts, but there was a 0.98-milliamp draw. We traced the parasitic draw back to the blower motor final stage; the final stage was shorted.
It’s essential to have a stable power supply connected to the battery when performing diagnostic test plans, CAN alignments, adaptations or programming on a BMW. We did. If the power supply isn’t stable, the ISTA will kick the car out of the procedure.
After the customer gave us the OK to replace the battery and final stage, we were able to perform the DME alignment procedure.
With the DME properly aligned with the other modules, we got a note at the end of the procedure stating that the DME was bad. We then ran the test on the DME and it came back as bad. We tried to reprogram the DME, but it would not take the programming. So we back-probed the complete engine wire harness to see if there was a problem that might have taken out the DME. The DME usually doesn’t fail on its own – there’s a short somewhere that has burned it out.
After testing the engine wire harness, we could not find a continuity problem. However, heat or vibrations could affect the wire harness when the engine is running, and we could not test for that.
So I had to decide whether or not to replace an expensive DME without a new engine wire harness and take a chance that the new DME may burn out. Ultimately, we installed a new harness and a used DME. Once both of those components were installed, we were able to perform all CAN alignment procedures and programming.
So we had five problems: a bad throttle body, a worn engine wire harness, a bad DME, a worn battery and a shorted final stage. We could see the bad throttle body from the beginning, but not the bad DME until the battery and final stage were replaced.