SCP (J1850) Invalid or Missing Data for Primary Id
Your vehicle's main computer isn't receiving proper communication data from another module on the CAN/SCP network bus. Think of it like a phone call where one person isn't speaking clearly enough for the other to understand.
The ECU monitors incoming SCP (J1850) bus messages from other modules for valid data packets with correct identifiers and checksums. When a primary ID message fails to arrive or contains corrupted data, the ECU logs this fault. The system expects consistent communication timing and valid data structure within defined intervals.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Message Valid Checksum | Checksum matches expected value | Checksum mismatch or missing data frame |
| Primary ID Reception Timeout | Message received within 100-500 ms intervals | No valid message received for 1+ seconds |
Code U1087 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, U1087 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.