SCP (J1850) Invalid or Missing Data for Cellular Phone / Paging System
Your vehicle's communication system is missing or receiving garbled data from the cellular/paging module, like a phone with no signal bars trying to send a text. The car's network can't properly talk to the telematics or emergency call system.
The ECU monitors the J1850 serial data bus for valid messages from the cellular/paging control module at regular intervals. When expected data frames are missing, corrupted, or absent for a specified duration, the ECU logs this fault. The system expects handshake acknowledgment and periodic status updates within defined timing windows.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| J1850 Data Frame Validity | Valid frames received every 100-500ms | Missing or invalid frames for >2 seconds |
| Cellular Module Response | Module responds to bus queries | No response or timeout on bus communication |
Code U1171 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, U1171 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.