SCP (J1850) Invalid or Missing Data for Navigation
Your vehicle's navigation system isn't communicating properly with the engine computer over the SCP bus network. Think of it like a phone line being disconnected—the devices need to talk, but the message isn't getting through.
The ECU monitors incoming SCP (J1850 protocol) bus messages from the navigation module to receive location and routing data. It expects valid data packets at regular intervals; if data is missing, corrupted, or arrives too late, the fault is triggered.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| SCP Bus Message Timeout | Data received every 50-200ms | No valid data for >500ms |
| Data Integrity Check | CRC/checksum valid | Checksum mismatch or corrupt payload |
Code U1233 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, U1233 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.