RCU family
RCU_a004_supplyOvervoltage
Backup power braking assist unavailable
What does the RCU_a004_supplyOvervoltage alert mean?
The Redundant Control Unit (RCU) power supply voltage is too high.
What you'll see in your Tesla
- Backup power braking assist unavailable
- OK to drive - Schedule service
What triggers it
The RCU power supply voltage is higher than 18 volts for 2 seconds or higher than 19 volts for 500 milliseconds.
When it clears
The RCU power supply voltage has returned below 17.5 volts.
Potential impact
The RCU may not be able to perform backup power braking assist.
Affected models
Model Y 2025+
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Alerts like this reach MyTeslaMate through your car's Tesla telemetry API. MyTeslaMate logs every alert your Tesla reports and turns it into readable history and real-time notifications — hosted TeslaMate with no server to run.