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U12C800 — MAC address conflict in Ethernet switch branch 1
MAC address conflict in Ethernet switch branch 1. The Taycan, 911 (992), Panamera (971), Panamera (972) and Cayenne report this code; below is which control unit sets it on each model and how to read and clear it.
Which models and control units set U12C800
How to read and clear U12C800
- Plug a standard ENET (Ethernet-to-OBD) cable into your Porsche's OBD port and your Mac or Windows PC.
- Open STEUER14, pick your car and run a fault scan: every control unit is read, and U12C800 shows with its status, its full description and the freeze frame when the unit stores one.
- Fix the cause first, then clear the fault memory and scan again to check it stays away. Reading and clearing fault codes is free on every control unit.
More about fault memory in the manual →
Download STEUER14 — free fault readingOther codes of the DC/DC Converter
| U112200 | Data bus - implausible message |
| U112300 | Data bus – fault value received |
| U11BB00 | Ethernet databus branch 1, Electrical error |
| U11BC00 | Ethernet databus branch 2, Electrical error |
| U122C00 | Ethernet databus branch 1, No communication |
| U122D00 | Ethernet databus branch 2, No communication |
| U12C900 | MAC address conflict in Ethernet switch branch 2 |
| U12CA00 | MAC address conflict in Ethernet switch branch 3 |
| U12CB00 | MAC address conflict in Ethernet switch branch 4 |
| U12D000 | IPv6 address conflict |
| U138F00 | Clock synchronization failure |
| U139000 | Clock synchronization master, branch 1, invalid number |
All 200 codes of this control unit →
Fault names come from the manufacturer's diagnostic data. STEUER14 is independent and not affiliated with Porsche AG. A code tells you what a control unit detected, not always which part failed — check wiring, supply voltage and related codes before replacing parts. STEUER14 shows each fault's full description, status and freeze frame on the car.