U0168
Lost Communication With Vehicle Security Control Module
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Code U0168 indicates that your vehicle's engine control module has lost communication with the vehicle security control module — the electronic system responsible for the anti-theft immobilizer, keyless entry, and alarm functions. This module verifies that the correct key or transponder is being used before allowing the engine to start, making it a critical gatekeeper for vehicle operation.
The most noticeable symptom is often a no-start condition. The security module's primary job is to prevent unauthorized engine starts, so when it goes offline, the vehicle's PCM may refuse to enable fuel injection or ignition as a security precaution. You may also notice that your key fob stops working for remote lock/unlock functions, the security light on the dashboard stays on or flashes, and the alarm system behaves erratically.
This code needs attention within the week, especially if it's causing a no-start condition. The most common causes are a weak battery or corroded electrical connections — check these first before assuming the worst. However, if the module itself has failed or its software is corrupted, a dealer visit is typically required because reprogramming involves re-registering the vehicle's keys to the new or repaired module, which requires manufacturer-specific diagnostic tools.
Severity
Symptoms
- •Security or immobilizer warning light illuminated or flashing on dashboard
- •Engine will not start even with the correct key or key fob
- •Key fob remote lock/unlock and panic button unresponsive
- •Door locks or power windows may not respond to interior switches
- •Alarm system fails to arm or triggers without cause
- •Vehicle may start but stall immediately due to immobilizer lockout
Likely Causes
The vehicle security module requires stable 12V power at all times. A blown fuse, weak battery, failing alternator, or corroded ground strap can cause intermittent or total power loss to the module.
Corroded pins, broken harness wires, or loose connectors between the security module and the vehicle's CAN bus network interrupt data flow. Even a single high-resistance joint can cause the module to appear offline.
Internal component failure from cracked solder joints, moisture intrusion, or burned circuitry prevents the module from transmitting or receiving CAN bus messages.
The security module requires a minimum of 9V at all times to maintain proper operation. A weak battery or intermittent voltage drops during cranking can cause the module to lose communication.
Power interruptions or voltage spikes can corrupt the module's firmware, requiring a dealer-level reprogramming to restore communication and proper anti-theft function.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Check battery health and charge or replace if weak
- Inspect and clean security module connector pins and ground points
- Check and replace blown fuses related to the security system
- Reprogram the vehicle security module with a dealer scan tool
- Replace the vehicle security control module and re-register keys