OBD-II trouble code
U0168: Lost Communication with Vehicle Security Control Module
A module on the network can no longer hear from the vehicle security / anti-theft control module. The immobilizer or alarm may misbehave and the engine may not start. Usually a power, ground, wiring, or connector fault.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- Medium severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $100 – $1,000
- DIY difficulty
- Shop recommended
What does U0168 mean?
U0168 is set when another module on the vehicle's communication network stops receiving messages from the vehicle security control module — the controller responsible for the anti-theft system, alarm, and on many vehicles the immobilizer that verifies the key before allowing the engine to start. It's a networked module that exchanges data with the engine computer and other controllers. When the network loses contact with it, the monitoring module logs U0168.
The causes follow the standard communication-code pattern: lost power or ground through a blown fuse, a corroded ground, or a wiring fault; a corroded, loose, or backed-out connector terminal; chafed, broken, or shorted CAN/bus wiring; an internally failed security module; or another module on the bus disrupting communication for everyone. Because the security system is sometimes integrated with the body control module or a dedicated immobilizer, it's worth confirming exactly which controller the vehicle uses and whether the security module is the only one missing.
The practical effect depends on how the vehicle handles a missing security module. On many vehicles the immobilizer is part of the security system, so if the engine computer can't confirm with the security module that a valid key is present, it won't allow the engine to start — a deliberate anti-theft behavior. That's why U0168 is rated medium severity and not reliably driveable: the car may crank but refuse to start, the alarm may behave erratically, and security warning lights may appear. Even when the engine does start, an unreliable security module is worth diagnosing promptly because it can leave you stranded.
Common causes
- Blown fuse feeding the vehicle security control module
- Corroded or loose ground at the security module
- Corroded, loose, or backed-out terminal at the module connector
- Chafed, broken, or shorted CAN/bus wiring to the security module
- Failed vehicle security / immobilizer control module
- Harness disturbed during alarm, remote-start, or accessory installation
- Water intrusion in a connector or harness
- Another module on the bus disrupting network communication
Symptoms
- Engine cranks but will not start (immobilizer not satisfied)
- Security or anti-theft warning light on or flashing
- Alarm arming, disarming, or sounding erratically
- Remote key fob functions intermittent or not working
- Scan tool cannot communicate with the security module
- Security-related messages in the driver information display
- Other modules may store communication codes alongside U0168
Diagnostic steps
- 1.Scan all modules and confirm the security module is the unreachable one while others respond — if several modules are missing, suspect the bus itself.
- 2.If a remote start, alarm, or accessory was recently installed, inspect that work first — it commonly disturbs security wiring.
- 3.Check the fuse feeding the security module and verify its power and ground.
- 4.Inspect the module connector for corrosion, looseness, and backed-out terminals.
- 5.Inspect the CAN/bus wiring to the module for chafing, breaks, and shorts.
- 6.If power, ground, and wiring are good but the module still won't communicate, replace and program it to the vehicle per the manufacturer procedure — security modules typically require anti-theft relearn.
Repair cost
$100 – $1,000
A blown fuse, corroded ground, or connector repair is the cheapest fix at $100-$300 plus diagnostic time. Repairing wiring runs $150-$500. Replacing the vehicle security / immobilizer module runs $300-$1,000+ including programming and the anti-theft relearn, which usually requires a manufacturer-level tool and valid keys. Correcting a faulty aftermarket alarm or remote-start install is a common and variable cost.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with module communication / can bus diagnosis preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.