Theft Deterrent Fuel Enable Signal Not Received/ B+ Supply To VCRM A/C Circuit Malfunction
Your vehicle's anti-theft system isn't communicating properly with the fuel control module, like a security guard who can't reach the gate operator. The car won't start or may cut fuel suddenly because the theft deterrent isn't giving the all-clear signal.
The ECM monitors voltage signals from the Vehicle Coded Radio Module (VCRM) or theft deterrent relay to verify authorization before enabling fuel. It checks for proper 12V supply to the VCRM circuit and expects a valid enable signal within specific timing after key-on. If this handshake fails or voltage is absent, the ECU blocks fuel delivery as a security measure.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| VCRM B+ Supply Voltage | 12-14V with key on | Below 10V or 0V detected |
| Fuel Enable Signal | Present within 2 seconds of key-on | Signal absent or delayed >5 seconds |
Code P1631 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, P1631 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.