U0168 — Lost Communication Vehicle Security Control Module

Generic OBD-II · all makesNetwork / communication

OBD-II code U0168 indicates that the vehicle's communication network has lost contact with the Vehicle Security Control Module (VSCM). This module is part of the anti-theft system and is responsible for immobilizer functions. The code sets when the VSCM fails to respond to periodic network messages, which can prevent the engine from starting or cause other security-related issues.

Symptoms

Engine cranks but does not start, often with a flashing security or immobilizer light
Security or anti-theft warning light illuminated on the dashboard
Other modules may also show lost communication codes (U-codes)
Intermittent no-start condition or stalling after starting
Remote keyless entry or push-button start may not function
Check Engine Light or other warning lights may be on

What causes it — most likely first

1. Faulty Vehicle Security Control Module

The VSCM itself may have failed internally due to age, heat, or electrical damage, causing it to stop communicating on the network.

2. Open or shorted communication bus wiring

Damaged, corroded, or broken CAN bus wires between the VSCM and the rest of the network can interrupt data transmission. This is often caused by chafing, pinched harnesses, or water intrusion.

3. Poor electrical connection at the VSCM

Loose, corroded, or pushed-back terminals in the VSCM connector can cause intermittent or complete loss of communication. This is common after module replacement or in high-humidity environments.

4. Blown fuse or power/ground issue to the VSCM

The module requires stable battery voltage and ground to operate. A blown fuse, corroded ground point, or wiring fault can prevent the VSCM from powering up.

5. Network bus fault (e.g., CAN bus short or termination problem)

A short to power, ground, or between bus wires, or a missing termination resistor elsewhere on the network, can disrupt communication for multiple modules, including the VSCM.

6. Faulty Powertrain Control Module (PCM) or other control module

In rare cases, the PCM or another module acting as a gateway may fail to relay messages, but this is the least likely cause and should only be considered after all other possibilities are ruled out.

How it's diagnosed

Use a scan tool to check for other communication codes (U-codes) in all modules. If multiple modules are offline, suspect a network bus issue rather than a single module.
Inspect the VSCM connector and wiring harness for obvious damage, corrosion, loose pins, or water intrusion. Pay special attention to areas where the harness may rub against metal.
Verify power and ground at the VSCM connector using a multimeter. Check the relevant fuse and ensure battery voltage is present with the key on.
Measure CAN bus resistance and voltage at the VSCM connector (typically 60 ohms across CAN High and Low with the battery disconnected, and around 2.5V on each line with the key on). Abnormal readings indicate a wiring or network fault.
Attempt to communicate with the VSCM using a scan tool. If no response, perform a module self-test if supported. If the module is dead, confirm power/ground and network integrity before condemning it.
If all wiring, power, and network tests pass but the VSCM still does not communicate, replace the VSCM. As a last resort, suspect the PCM or another module, but only after a thorough diagnostic process.

Code facts & related codes

SystemNetwork / communication

StandardizationSAE generic — identical on every make

Frequently asked

Can I drive my vehicle with a U0168 code?

It depends. If the engine starts and runs normally, you may be able to drive, but the security system is compromised and the vehicle could fail to start later. If the engine does not start, the vehicle is not drivable.

Is the most common fix replacing the Vehicle Security Control Module?

Often yes, but only after ruling out wiring and power issues. Many VSCMs are replaced unnecessarily when the real problem is a corroded connector or broken wire. Proper diagnosis is essential.

Do I need to replace the PCM for a U0168 code?

Almost never. The PCM is rarely the cause of a lost communication code with the security module. Replacing the PCM is expensive and usually does not fix the problem. Exhaust all other diagnostics first.

Will a U0168 code clear itself?

The code may become a history code if communication is restored intermittently, but the underlying problem will not fix itself. The code will return if the fault persists.