An unexpected issue arose during a recent ride on a Bonneville Speedmaster: the cruise control malfunctioned, followed by rough engine performance and a laggy throttle. The engine eventually died and wouldn’t restart, despite the starter cranking. Interestingly, there were no fault lights or error codes displayed on the instrument panel or through TuneECU and an OBD2 reader. However, the OBD2 reader revealed a critically low battery voltage reading of just over 6 volts.
Further investigation showed the battery itself was healthy, registering 13 volts. Even connecting an external battery via roadside assistance failed to start the bike. Confusingly, other electrical components like the instrument panel, fuel pump (initially), and headlight functioned normally. This pointed towards a discrepancy between the actual battery voltage and what the bike’s computer (ECU) was registering.
Back home, further testing revealed a seized throttle solenoid, which subsequently threw an error code and stopped functioning. The fuel pump also ceased operation. The voltage reported on the CAN bus plummeted further to 5 volts, potentially explaining the failure of these components.
The primary suspect is a fault within the electrical system, possibly a corroded connection or a short circuit caused by the failing throttle solenoid. A thorough inspection of the wiring and components will be necessary to pinpoint the problem. Disconnecting components like the throttle solenoid and manipulating wiring harnesses might reveal voltage fluctuations, helping to isolate the affected area. Hopefully, the issue lies within the wiring and not the ECU itself. Further diagnostics will focus on identifying the root cause of the low voltage reading reported by the ECU to the OBD2 reader.
