It’s a common scenario for car enthusiasts and DIY mechanics to reach for a generic OBDII scan tool to quickly read fault codes. However, a recent experience highlights a potential pitfall when using these tools, even for seemingly simple tasks like reading diagnostic codes. In an unexpected turn of events, using a generic OBDII scanner inadvertently caused a malfunction in the steering angle sensor (SAS) of a vehicle. This incident serves as a cautionary tale about the complexities of car diagnostic systems and the importance of understanding the potential interactions between diagnostic tools and vehicle components.
The issue surfaced when, prior to utilizing dedicated Lotus 20/20 software, a generic OBDII scan tool was employed to check for any existing fault codes. Surprisingly, this action alone resulted in the steering angle sensor ceasing to function correctly. Upon subsequently using the Lotus software, it became apparent that the SAS was no longer transmitting CAN messages and was showing as uncalibrated.
To understand the root cause, a detailed analysis of the CAN bus was performed, comparing it to a previous, normal log. This investigation revealed a critical change: the steering angle sensor’s CAN ID had been altered to 0, instead of its original 0x85. While the exact sensor datasheet wasn’t specified in the original context, Bosch provides relevant documentation for steering wheel angle sensors that can help illustrate the technical aspects involved.
It’s hypothesized that the generic scan tool, in the process of requesting fault codes (typically using the 0x03 command), inadvertently sent a command that, in this specific Bosch SAS, is also used to zero the calibration or start angle. Crucially, in this scenario, it also mistakenly reset the CAN ID to 0x0. The resolution involved sending a specific command, 0x5308, to CAN ID 0x6F1. This action successfully restored the SAS to its correct CAN ID of 0x85. The command translates to the hexadecimal nibbles 0x3 0x5 0x8 0x0 over the CAN bus.
It’s important to note that the CAN ID for configuring the SAS appears to be consistently 0x6F1. The issue lies in the broadcast or output address, which can be easily erased or reset to 0x0. Therefore, if a CAN bus scan reveals data being broadcast on address 0x0, it’s highly likely a similar incident has occurred.
This situation is less common in vehicles where the steering angle sensor operates on a dedicated diagnostic CAN bus. However, in certain car models, the SAS is directly connected to the OBD port, making it vulnerable to unintended commands from generic scan tools. This experience underscores the need for caution when using non-specific diagnostic equipment, especially on systems where critical sensors are directly accessible via the OBD port. Always ensure you understand the potential interactions of your diagnostic tools with your vehicle’s specific systems to avoid unexpected complications when using a Fixed Car Diagnostic Tool or any generic scanner.
