SCP (J1850) Invalid or Missing Data for Ignition Switch / Starter
Your vehicle's onboard computer isn't receiving proper data from the ignition switch through the SCP (J1850) communication bus. It's like a phone unable to receive a text message from a specific contact—the connection exists but the data isn't getting through.
The ECU monitors the SCP data bus for valid ignition switch position signals (Off, Accessory, Run, Start). When the bus fails to deliver this critical message within the expected timeframe or with correct formatting, the ECU sets the fault. The system expects a consistent handshake every scan cycle.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| SCP Bus Signal Presence | Valid data received every 10-20ms | No data or corrupted signal for >100ms |
| Ignition Switch Status Message | Clear position code (0=Off, 1=Acc, 2=Run, 3=Start) | Missing, invalid, or unreadable position code |
Code U1135 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, U1135 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.