U0168 – Lost Communication With Vehicle Security Control Module

System: Network | Standard: ISO/SAE Controlled | Fault type: General

Definition source: SAE J2012/J2012DA (industry standard)

DTC U0168 indicates a network communication problem: the vehicle’s other controllers have detected a loss of communication with the Vehicle Security Control Module. This is not a “bad module” verdict by itself; it means required messages on the vehicle network were missing for long enough to set a fault. The exact conditions that trigger U0168, the timeout logic, and which modules are involved can vary by vehicle, so confirm the monitor description, network topology, and connector locations using the correct service information. Because security functions may interact with immobilizer, alarm, key recognition, or authorization logic (varies by vehicle), the impact can range from a stored code to a no-start condition.

What Does U0168 Mean?

U0168 – Lost Communication With Vehicle Security Control Module means one or more control modules on the vehicle network determined they can no longer reliably exchange data with the Vehicle Security Control Module. Under SAE J2012 DTC structure, “U” codes relate to network communication, and this specific entry is defined strictly as a loss of communication with that module. In practice, the code sets when expected network messages from the Vehicle Security Control Module are absent, corrupted, or not acknowledged beyond a calibrated time window. The DTC points you toward network integrity, module power/ground, and connector/wiring conditions that prevent normal communication.

Quick Reference

  • Subsystem: Network communication with the Vehicle Security Control Module (data bus messaging).
  • Common triggers: Module offline, network open/short, high resistance at connectors, low system voltage during crank, or intermittent power/ground to the security module.
  • Likely root-cause buckets: Wiring/connector issues, power/ground faults, network bus faults, module internal fault, configuration/programming issues (varies by vehicle).
  • Severity: Varies; may be a warning-only condition or may affect starting/authorization and security features.
  • First checks: Verify battery/charging health, scan for related U-codes, confirm module appears on the network, and inspect power/ground and network connectors.
  • Common mistakes: Replacing the security module before verifying power/ground, network continuity, connector pin fit, and whether another module is the true source of bus disruption.

Theory of Operation

The Vehicle Security Control Module exchanges identification and status information with other modules over the vehicle network. Depending on platform design, it may participate in functions such as theft deterrent status, key/credential recognition, alarm state, and authorization messages needed by other controllers. Each module expects certain messages at a regular interval and may also require successful message validation (such as counters or checksums) before considering the data “alive.”

U0168 sets when one or more modules determine the Vehicle Security Control Module is no longer communicating. Common reasons include the security module losing power or ground, an open or short affecting the network wiring to that module, or poor terminal contact causing intermittent dropouts. Some vehicles may log the fault as current when the module is fully offline, or as history when communication resumes after an interruption.

Symptoms

  • Warning indicators: Security or general warning lamps/messages may illuminate (varies by vehicle).
  • No-start: Engine may crank but not start, or starting may be inhibited (varies by vehicle design).
  • Intermittent start: Starts normally at times, then fails after a power cycle or vibration-related dropout.
  • Remote functions: Remote lock/unlock, alarm arming, or passive entry features may be inoperative or inconsistent (varies by vehicle).
  • Multiple U-codes: Additional network communication codes may be stored in several modules.
  • Lost module data: Scan tool may show the security module not responding or appearing/disappearing during a session.

Common Causes

  • Open, shorted, or high-resistance network wiring between the vehicle security control module and the rest of the vehicle network
  • Poor connector contact (spread terminals, corrosion, contamination, loose locking) at the vehicle security control module or at an in-line network connector/junction
  • Power supply issue to the vehicle security control module (blown fuse, faulty relay, poor feed connection, excessive voltage drop under load)
  • Ground circuit problem for the vehicle security control module (loose ground fastener, corrosion at ground point, high resistance in ground lead)
  • Module not waking up or going to sleep incorrectly due to a wake/sleep control issue (varies by vehicle network design)
  • Network bus fault affecting multiple modules (short between network lines, short to power/ground, or a termination issue, depending on network type)
  • Recent electrical work or accessory installation causing disturbed wiring, back-probing damage, or pin fit issues near the module or network harness
  • Vehicle security control module internal fault (hardware/software) preventing it from transmitting/receiving expected messages

Diagnosis Steps

Tools that help for U0168 include a scan tool capable of full-network scans and module communication checks, a digital multimeter for voltage-drop and continuity testing, and service information for network topology, connector pinouts, fuse/ground locations, and wake/sleep behavior. Back-probe leads and terminal test adapters are strongly recommended to avoid spreading terminals during testing.

  1. Confirm the DTC context. Perform a full vehicle scan and record all codes and which modules report U0168. Save freeze-frame/environment data and note whether the vehicle security control module is listed as “offline” or “no communication.”
  2. Check for broader network issues first. If multiple “lost communication” codes are present across many modules, treat this as a network-wide concern before focusing on the vehicle security control module alone. Use service information to identify which network segment is involved.
  3. Attempt direct communication with the vehicle security control module. Using the scan tool, try to enter the module and read identification/data. If communication is possible, clear codes and proceed with an intermittent/connection-focused strategy. If communication is not possible, proceed with power/ground and network circuit testing.
  4. Verify battery voltage integrity and basic electrical health. Check battery state of charge and inspect battery terminals for looseness/corrosion. Poor system voltage stability can create communication dropouts and misleading network codes.
  5. Inspect fuses/relays feeding the module. Using service information, identify all module power feeds (constant and switched, if applicable). Check fuses and related relays, then verify the module receives power at the connector. Do not rely on visual fuse inspection alone; test for power on both sides under the correct key state.
  6. Perform voltage-drop testing on power and ground. With the circuit loaded (key state as required by service information), measure voltage drop across the module power feed path and across the ground path. Excessive drop indicates resistance in wiring, connectors, splices, relay contacts, or ground points that can prevent stable network operation.
  7. Check connector condition and terminal fit. Disconnect the module connector(s) and inspect for corrosion, moisture, bent pins, pushed-out terminals, and damaged seals. Gently verify terminal tension/retention using appropriate terminal tools (do not “pin drag” with oversized probes).
  8. Wiggle test while monitoring communications. Reconnect as needed and perform a controlled harness/connector wiggle test at the module, nearby splices, and any junction connectors while observing the scan tool’s module online status and network DTC setting behavior. If the fault toggles, isolate the exact location.
  9. Verify network circuit integrity. With the module disconnected (as appropriate for the network and service procedures), check the network circuits for opens/shorts between the network lines and for shorts to power/ground. Use service information to determine which pins are network circuits and what checks are valid for the specific network type.
  10. Compare readings at two points to locate the fault. If a network line shows an abnormal condition at the module connector, repeat the same check at a nearer junction/splice or at another accessible module on the same segment. A difference between points helps localize the harness section or connector at fault.
  11. Check wake/sleep behavior and intermittent resets. If the issue occurs after key-off or during startup, use live-data logging (where available) to monitor module status, network activity, and related power-mode signals. Look for patterns that suggest the module is not powering up, is resetting, or is dropping off the bus during specific transitions.
  12. Only after wiring/power/ground/network checks pass, evaluate the module. If the module has correct power/ground, network circuits test good, and the issue persists (especially with no scan tool communication), follow service information for module testing, programming, or replacement procedures (varies by vehicle).

Professional tip: When U0168 is intermittent, focus on reproducing the dropout while logging network/module status and simultaneously performing targeted wiggle testing and voltage-drop checks. Intermittent communication faults are commonly caused by marginal terminal tension or high resistance at a power/ground splice that looks visually acceptable but fails under vibration or load.

Need network wiring diagrams and module connector views?

Communication stop and network faults require module connector pinouts, bus wiring routes, and power/ground diagrams. A repair manual helps you trace the exact circuit path before replacing any ECU.

Factory repair manual access for U0168

Check repair manual access

Possible Fixes & Repair Costs

Repair costs for U0168 vary widely because the fix depends on what actually caused the network communication loss, how accessible the wiring and connectors are, and whether power/ground, network integrity, or a module fault is confirmed during testing.

  • Repair or replace damaged network wiring (open circuits, shorts between network lines, or shorts to power/ground) after confirming the fault with continuity and isolation testing
  • Clean, repair, or replace compromised connectors (corrosion, backed-out terminals, poor pin fit) and ensure proper terminal tension where applicable
  • Restore proper power and ground to the vehicle security control module by repairing the affected fuse, feed circuit, ground point, or high-resistance connection verified by voltage-drop testing
  • Correct network connection issues at junctions/splices by reworking an overheated, loose, or high-resistance splice pack after pinpoint testing
  • Perform a verified module configuration/setup procedure if required by the platform after power loss or module replacement (varies by vehicle and service information)
  • Replace the vehicle security control module only after confirming power/ground and network circuits are correct and the module remains non-communicative or repeatedly drops offline

Can I Still Drive With U0168?

You may be able to drive with U0168 if the vehicle starts and no critical warnings are present, but treat it as a security/network reliability concern. A lost-communication fault can lead to intermittent no-start, immobilizer-related issues, warning messages, or other modules setting additional communication DTCs. If you experience stalling, a no-start condition, reduced power, or multiple warning indicators that affect braking/steering, do not drive—diagnose the network and module power/grounds first.

What Happens If You Ignore U0168?

Ignoring U0168 can allow an intermittent network or power/ground problem to worsen, increasing the chance of random no-start events, intermittent security-related malfunctions, repeated warning messages, and cascading communication faults across the vehicle network. In some cases, a marginal connection can become a complete open circuit, leaving the vehicle security control module offline and making the condition harder to reproduce and diagnose.

Compare nearby lost vehicle trouble codes with similar definitions, fault patterns, and diagnostic paths.

  • U0167 – Lost Communication With Vehicle Immobilizer Control Module
  • U017D – Lost Communication With Control Module “M”
  • U017C – Lost Communication With Control Module “L”
  • U017B – Lost Communication With Control Module “K”
  • U017A – Lost Communication With Control Module “J”
  • U0179 – Lost Communication With Control Module “I”

Key Takeaways

  • U0168 indicates a loss of communication with the vehicle security control module, not a confirmed component failure by itself
  • Most root causes fall into wiring/connector faults, power/ground issues, or network integrity problems; module failure is a later conclusion
  • Confirm the concern with a full-network scan and verify module power/ground before suspecting the module
  • Intermittent faults are common; use wiggle testing and data logging to capture dropouts
  • Driving may be possible, but the risk of intermittent no-start or escalating network faults increases if left unaddressed

Vehicles Commonly Affected by U0168

  • Vehicles using a dedicated vehicle security control module that communicates on a shared in-vehicle network
  • Vehicles with immobilizer or theft-deterrent functions integrated across multiple modules via network messaging
  • Vehicles with multiple network buses and gateway routing between subsystems
  • Vehicles with security-module wiring routed through areas prone to movement or pinch points (varies by vehicle)
  • Vehicles that have experienced battery issues, recent battery replacement, or low-voltage events that can expose marginal connections
  • Vehicles with prior electrical repairs affecting harness routing, connectors, splices, or grounds (varies by vehicle)
  • Vehicles operated in conditions that can accelerate connector corrosion (varies by vehicle environment and design)
  • Vehicles with aftermarket electrical additions that share power, grounds, or harness routing near network circuits (varies by vehicle)

FAQ

Does U0168 mean the vehicle security control module is bad?

No. U0168 only indicates that other modules detected a loss of communication with the vehicle security control module. The cause could be a power/ground problem, wiring/connector damage, network circuit faults, or the module itself. Confirm power, ground, and network integrity before considering module replacement.

Can a weak battery or recent battery disconnect cause U0168?

It can contribute, depending on the vehicle. Low voltage, unstable system power, or an interrupted power supply can cause modules to reset or drop off the network, which may set a lost-communication DTC. If U0168 returns after the electrical system is stable, focus on power/ground connections and network wiring rather than the battery alone.

Why do I also see multiple U-codes with U0168?

Communication networks are shared. If the vehicle security control module goes offline, other modules may report additional communication DTCs because messages they expect are missing. Diagnose the network systematically and prioritize the codes that indicate which module is not communicating and whether a bus-wide fault is present.

What is the first thing to check for U0168?

Start by confirming whether the vehicle security control module communicates with a scan tool. Then verify its power and ground circuits under load using voltage-drop testing, and inspect its connectors for corrosion, loose terminals, or damage. If power/ground are correct, move to network circuit checks for opens/shorts and intermittent dropouts.

If I clear U0168 and it comes back, what does that indicate?

A returning U0168 indicates the communication loss is still occurring or is intermittent. This commonly points to an unstable connection (poor pin fit, corrosion, harness stress), a marginal power/ground feed, or a network wiring fault that reappears with vibration or temperature changes. Use live-data logging and a controlled wiggle test to capture when communication drops.

For an accurate repair plan, confirm whether the vehicle security control module is non-communicative or intermittently dropping offline, then verify power, ground, and network integrity before replacing any modules.