SCP (J1850) Invalid or Missing Data for Primary Id
Your vehicle's main computer isn't receiving critical data messages from another control module through the communication network. It's like a walkie-talkie conversation where one person stopped transmitting their ID, so the receiver doesn't know if the message is valid.
The ECU monitors the SCP (Standardized Corporate Protocol) J1850 bus for valid data packets with proper Primary ID headers from modules like the Transmission Control Module or Body Control Module. When expected message IDs fail to arrive or contain invalid data within a set time window, the fault triggers.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Message ID Validity | Primary ID present and valid in each CAN/SCP frame | Primary ID missing, corrupted, or timeout exceeded |
| Message Reception Interval | Data received within 100-500ms cycles | No valid message received for >500ms duration |
Code U1102 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, U1102 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.