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As a car owner, you may be unfamiliar with BSD bus communication failures, but you have likely encountered issues caused by it, such as the water pump running continuously, inability to measure oil, inability to reset after oil maintenance, emergency power generation by the generator, and insufficient battery power. Therefore, BSD bus communication failures can be said to be quite common in BMW repairs. Here are a few tips:
1.Why do BSD bus issues cause so many seemingly unrelated failures?
BSD is a type of serial data interface controlled by the engine computer (DME). As shown in the image above, there are three components connected to the BSD bus: the water pump, oil level sensor, and generator. Since the DME provides serial data to all modules instead of separately to each module, if any one of them has an issue, it can cause an entire BSD bus communication failure. This can lead to seemingly inexplicable causal relationships, such as inability to measure oil, where the root cause turns out to be a problem with the water pump’s wiring.
2.How to check?
For BSD bus communication failures, we can only eliminate possibilities one by one. For example, if your current issue is the inability to measure oil, disconnect the water pump, oil level sensor, and generator from the BSD one by one, then perform an oil measurement or check the BSD waveform. If disconnecting the water pump restores the measurement (BSD waveform normal), it indicates a problem with the water pump and its wiring. If disconnecting the generator restores the measurement, it indicates a problem with the generator and its wiring.
If disconnecting all components still does not resolve the issue, it is likely a fault with the DME computer itself. For safety, you can directly measure the BSD signal pins on the DME, checking their signal voltage, which is typically 8-10V.
For faults with the DME computer itself, it is generally due to damage to the internal communication chip, but few places can repair chips; most can only replace the DME computer. Additionally, for the N52 engine, there was a related technical bulletin in the past, indicating that a batch of poor-quality ignition coils could damage the DME’s internal chip, leading to BSD bus communication failures. Therefore, it is advisable not to use aftermarket ignition coils.