Telematics Control Unit (TCU) backup battery powers your car's emergency tracking, location broadcast, and SOS/eCall communication systems if the main car battery disconnects or fails during an accident. When this battery degrades (typically after 5 to 7 years), it triggers a dashboard error such as "SOS System Inactive" or "SOS Limited Functionality".
Typical Symptoms of Failure
- Dashboard Warning Lights: Messages explicitly flagging the SOS system or eCall emergency failure.
- Loss of Connectivity: Occasional drops in Bluetooth or built-in vehicle tracking.
- System Fails Diagnostic Checks: The TCU conducts a periodic internal self-test; a failing battery drops below voltage thresholds and trips the fault
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