U0168

Code

Generic U — Network/User

Lost Communication With Vehicle Security Control Module

Brand: Generic

Type: U — Network/User

Views: UK: 19 EN: 78 RU: 38

AI status

Completed

ready

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Page language: EN

Causes

Blown fuse or loss of power to the security control module
Poor or missing ground at the module
Damaged or disconnected wiring or connector to the security module
CAN/LIN network fault (open/short/low termination or high error rate)
Failed security control module (internal electronic fault)
Aftermarket alarm/remote start or incorrect installation interfering with the bus

Symptoms

Security/immobilizer warning lamp illuminated or flashing
Vehicle may not start or crank (immobilizer preventing engine start)
Remote keyless entry, keyless start or alarm functions inoperative
Other modules report network communication DTCs
Door locks, trunk release or interior lights behave erratically
Intermittent or permanent loss of body network devices

What to check

Verify battery voltage (>=12.4 V nominal) and good charge state
Use a scan tool to read U0168 and list network modules present/absent
Check fuses related to the security/control module and replace if blown
Inspect connectors and wiring at the security module for corrosion, bent pins, or disconnection
Check for aftermarket alarm/remote-start components and temporarily disconnect them
Verify module power and ground with a DVOM at the module connector

Signal parameters

Battery voltage at module: typically 12–14.5 V (engine running 13.5–14.5 V)
CAN idle voltages (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (both near mid-rail)
CAN dominant voltages: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V when active; differential ≈ 2 V
Termination resistance: ~60 ohms measured across CAN_H and CAN_L (two 120 Ω in parallel)
Expected message rate: security module message IDs and periodic heartbeat frequency vary by vehicle — typically 1–10 Hz for heartbeat/status messages
CAN bus error counters and 'bus-off' status reported by some scan tools

Diagnostic algorithm

Reproduce/confirm: Connect a capable scan tool, confirm U0168 is present and note freeze frame/occurrence history and any related U-codes.
Battery & basics: Verify battery state of charge and charging system. Recharge or stabilize battery if low and clear codes to retest.
Visual: Inspect security module connector, harness and nearby components for damage, rodent chew, corrosion, water intrusion or poor pin contact.
Fuses & power/ground: Locate and test fuses for the security module. Back-probe/check for ignition-switched and constant power at the module pins and verify solid ground(s).
Network presence: Use the scan tool to view module list/addresses on the network. If the security module does not appear, attempt to communicate at the module connector.
Measure CAN signals: With ignition on (engine off) measure CAN_H and CAN_L at the module and at the data bus gateway. Check recessive and dominant voltages and compare to reference values.
Termination & shorts: Measure resistance between CAN_H and CAN_L with ignition off (~60 Ω). Check for short to 12 V or ground on either CAN line.
Isolate bus segments: If multiple networks or gateways exist, isolate the segment with the security module by disconnecting other modules or aftermarket devices to find the failing element.
Check for bus errors: Monitor live CAN traffic with a scope or advanced scan tool. Look for error frames, bus-off conditions, or missing periodic messages (heartbeat).
Aftermarket interference: Temporarily disconnect any aftermarket alarm, remote starter or immobilizer bypass and retest communications.
Module reset/relearn: If wiring, power and bus are good, try a controlled power-cycle and clear codes. Follow manufacturer procedure for module reset or reprogramming if required (use correct security/key programming tools).
Replace or reprogram: If all wiring, power, grounding and bus integrity are good and the module still does not communicate, consult service manual for authorized module replacement and reprogramming/relearning procedures.

Likely causes

Fuse for security module or related power circuit blown
Corroded, loose or damaged connector at the module
Short or open on CAN high or CAN low between module and gateway
Aftermarket alarm or bypass device connected to security wiring
Module has gone 'bus-off' due to repeated CAN errors
Battery voltage low (

Fault status

⚠️ Status

Lost Communication With Vehicle Security Control Module (U0168): The vehicle network did not receive expected messages from the Security/Immobilizer module. Check module power, ground, connectors, wiring/CAN bus integrity, termination, and for interfering aftermarket devices. Module failure or software issues can also cause this code.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-3.0 hours