U0168

Universal

Lost Communication With Vehicle Security Control Module

Definition source: General OBD-II reference catalog
Definition verification: Not independently verified for display.
Time: Varies by diagnosis and vehicle | Diagnostic difficulty: Medium
Medium Severity

The vehicle has detected that one or more control modules cannot communicate with the vehicle security control module over the vehicle network. This module may support functions such as theft deterrence or authorization to start, depending on the vehicle. The code does not prove that the security module itself has failed; a power, wiring, network, or connection issue can also interrupt communication.

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⚠️ Before You Begin (Safety First)

If the vehicle will not start, stalls, or has an active security warning, avoid relying on it until the issue is diagnosed. Do not bypass the anti-theft system or probe safety-system circuits. If the vehicle otherwise operates normally, arrange diagnosis soon and stop driving if it becomes unreliable or unsafe.

Common Symptoms

  • There may be no noticeable symptoms if the communication loss is intermittent or the affected function is not currently needed.
  • A security or anti-theft warning may appear if the vehicle cannot receive status from the security control module.
  • The vehicle may fail to start or may have intermittent starting trouble if starting authorization depends on this module.
  • Remote entry, alarm, or other security-related functions may behave intermittently or stop working, depending on the vehicle's design.

Common Causes

  • A weak battery or interrupted power supply may cause a control module to reset or stop communicating.
  • A blown fuse, poor ground, loose connector, corrosion, or damaged wiring may interrupt power or communication to the security module.
  • A fault elsewhere on the vehicle network may prevent modules from exchanging messages.
  • An aftermarket alarm, remote-start device, or other added equipment may interfere with wiring or network communication.
  • The security control module may have an internal fault, but this should be considered only after its power, grounds, connections, and network path are checked.

Diagnostic Steps

  1. Note any security warnings, starting problems, or changes to alarm and remote-entry operation; these details help identify which functions are affected.
  2. Check that the battery is secure and that its terminals are clean and tight. Low or unstable vehicle voltage can interrupt module communication.
  3. With the vehicle off, check the owner's manual for fuses related to the security system or control modules. Replace a failed fuse only with the specified type and rating; if it fails again, seek diagnosis.
  4. Look for obvious damage, looseness, or corrosion at accessible wiring and connectors without forcing them apart. Avoid touching unfamiliar safety-system wiring.
  5. Have the vehicle scanned for codes in all available modules. Related communication codes can help distinguish a module-specific problem from a wider network or power-supply issue.

When to Call a Professional

Use a scan tool that can communicate with all vehicle modules. Check whether other modules report communication faults, then follow vehicle-specific service information to inspect the security module's power, grounds, connectors, and network wiring. Confirm the fault and its cause before replacing a module; programming or configuration may be required if a module is replaced.

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Commonly Asked Questions

Does U0168 prove the vehicle security control module is bad?

No. It indicates lost communication, which can result from a power, ground, connector, wiring, or network problem as well as an internal module fault.

Can U0168 cause a no-start?

It can, if the vehicle relies on the security control module for starting authorization. The effect varies by vehicle, so other causes of a no-start should also be checked.

Can I keep driving with this code?

If the vehicle starts and operates normally, the code may not immediately affect driving, but security or starting functions could be unreliable. Stop driving if the vehicle stalls or becomes unsafe, and arrange diagnosis.

Should I replace the security module or clear the code first?

Do not replace the module based on this code alone. A technician should check related codes, module power and grounds, connectors, and network communication. Clearing the code without finding the cause may only hide the symptom temporarily.

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