SCP (J1850) Invalid or Missing Data for Odometer
Your vehicle's odometer data isn't reaching the engine computer properly, like a radio losing its signal. This is a communication problem between the instrument cluster and the main computer.
The ECU expects valid odometer mileage data packets via the SCP (J1850) serial communication bus every scan cycle. When the instrument cluster fails to transmit valid data or the signal integrity is lost, the ECU detects missing or corrupted odometer information and logs this network fault.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| SCP Bus Odometer Data | Valid data received every 100-500ms | No valid data or corruption for >2 seconds |
| Odometer Increment Rate | Matches vehicle speed logic | Zero change or invalid format detected |
Code U1123 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, U1123 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.