Anti Theft System
Your vehicle's anti-theft system isn't communicating properly with the engine computer, like a security guard who can't verify your ID. The car may not start or may disable itself as a safety measure.
The ECM monitors the immobilizer module's handshake signal to verify the correct key/transponder is being used. It validates the security token communication between the key fob, immobilizer control module, and engine computer. If this authentication fails or times out, the ECM locks out fuel injection.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Immobilizer Signal Verification | Valid token received within 500ms of key insertion | Invalid or missing token; authentication timeout |
| Key-to-ECM Communication | Continuous valid CAN/UART message exchange | Message dropout or corruption detected |
Code P1629 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, P1629 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.