SCP (J1850) Invalid or Missing Data for Vehicle Security
Your car's security system isn't communicating properly with the engine computer over the vehicle's internal network. It's like a security guard unable to radio headquarters, so the system doesn't know if the key is legitimate.
The ECU monitors SCP (J1850) bus messages from the security module to verify valid key/immobilizer data. If security data frames are missing or corrupted on the CAN/J1850 bus for a set duration, the fault triggers. The ECU expects periodic valid security handshake signals within defined time windows.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Security message timeout | Valid data received every 100-500ms | No valid security data for >2 seconds |
| Data integrity check | Checksum/CRC valid | Checksum failure or corrupted frame |
Code U1146 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, U1146 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.