SCP (J1850) Invalid or Missing Data for Vehicle Motion
Your vehicle's communication network isn't receiving speed or motion data from the transmission control module, like a driver missing critical gauges on the dashboard. The ECU can't confirm the car is actually moving, which disrupts engine timing and transmission coordination.
The ECM monitors the SCP (J1850) bus for vehicle speed and transmission state data transmitted by the TCM every few milliseconds. If this message stream stops, times out, or contains invalid checksums for more than a threshold period, the fault sets. The ECM cannot confirm motion status needed for fuel and spark timing optimization.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| SCP Bus Message Timeout | Valid message received every 10-50ms | No valid message for >500ms |
| Vehicle Speed Data Validity | Speed signal consistent with engine RPM | Missing, corrupted, or logically impossible values |
Code U1133 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, U1133 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.