SCP (J1850) Invalid or Missing Data for Primary Id
Your vehicle's main computer isn't receiving critical data from the transmission control module over the communication bus—think of it like a phone call where one person isn't speaking loud enough to be heard. Without this data, the vehicle may experience shifting issues or reduced performance.
The ECM continuously monitors the SCP (J1850) bus for valid data packets from the transmission control module, including gear position, line pressure, and shift commands. The bus expects periodic messages at specific intervals with valid checksums and identifiers to confirm active communication.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| SCP Bus Message Rate | Messages received at expected frequency | Missing or invalid primary ID messages for >2 seconds |
| Data Checksum Validity | Checksum matches calculated value | Checksum mismatch or corrupted primary ID field |
Code U1142 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, U1142 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.