SCP (J1850) Invalid or Missing Data for Primary Id
Your vehicle's computer isn't receiving proper communication data from a critical module over the J1850 network bus—think of it like a phone call where one person isn't talking clearly. This prevents the ECU from getting essential information needed to control engine functions properly.
The ECU monitors incoming SCP (J1850) bus messages from transmission, ABS, and other modules for valid data frames at regular intervals. When expected primary ID messages fail to arrive or contain corrupted data, the ECU flags a fault to prevent using invalid parameters for engine control.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| SCP Message Arrival Time | Within 10-100ms per module | Missing or delayed >500ms |
| Data Validity Check | Valid CRC/checksum pass | Checksum mismatch or corrupt bits |
Code U1055 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, U1055 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.