SCP (J1850) Invalid or Missing Data for Digital Signal Processing
Your vehicle's network communication bus (J1850 SCP) is missing or corrupted data needed for digital processing, like a radio station broadcasting a weak or interrupted signal. The ECU can't properly receive critical information from other modules to make engine decisions.
The ECM monitors the J1850 SCP communication bus for valid data frames from transmission control, ABS, and other modules. It validates message checksums and timing intervals to ensure data integrity. If expected messages don't arrive within specific time windows or contain checksum errors, the fault is triggered.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Message Arrival Interval | 20-100 ms depending on module | Missing or delayed >500 ms |
| Checksum Validity | All bytes match calculated checksum | Checksum mismatch detected |
Code U1157 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, U1157 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.