U0168

Lost Communication With Vehicle Security Control Module

U0168 is a generic OBD-II network diagnostic trouble code: Lost Communication With Vehicle Security Control Module. It is logged by the engine control unit when the network monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
U0168
Group
Network
System
Network
Severity
Warning (MIL on, possible limp mode)
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What U0168 means

U0168 is set when the ECM, PCM, or a gateway module stops receiving expected messages from the Vehicle Security Control Module (VSCM) -- the node responsible for immobiliser, transponder-key authentication, and alarm-system control. On modern vehicles, the ECM queries the VSCM over the serial data bus to confirm that a valid key is present before authorising fuel injection and ignition output. Loss of this communication therefore carries a significant risk of no-start or engine shutdown depending on the platform's security strategy.

Some calibrations enter a timed failsafe that permits the engine to continue running for a short period after communication is lost (to avoid a sudden shutdown while driving), then immobilise at the next key cycle. Others apply immediate limp-mode fuelling restrictions. The exact behaviour is manufacturer-specific and must be verified against technical service documentation.

Diagnosis must address both the network communication fault and any underlying security-system hardware fault before releasing the vehicle, because a partially repaired system could leave the vehicle vulnerable to theft or could fail the immobiliser at an inconvenient time. Battery state is particularly important to check here, as low voltage during startup is a common trigger for transient security-bus faults.

Common causes

Most-frequently reported root causes when U0168 is logged.

  • 1
    Open, short, or high-resistance fault on the CAN bus wiring between the ECM and VSCM.
  • 2
    Failed Vehicle Security Control Module (immobiliser transponder receiver or processor fault).
  • 3
    Damaged or missing ignition-key transponder causing the VSCM to fault internally.
  • 4
    Blown fuse or open ground for the VSCM supply circuit.
  • 5
    Battery voltage too low to power the VSCM reliably during cranking.
  • 6
    Corroded harness connector at the VSCM (often located near the steering column, exposed to moisture).
  • 7
    ECM replacement without performing the required immobiliser pairing procedure.

Symptoms drivers notice

MIL illuminated; security indicator lamp may also be on or flashing.
Engine cranks but will not start (immobiliser active).
Engine starts briefly then stalls after the security timeout expires.
Alarm system may not arm or disarm correctly.
Remote keyless entry functions may be inoperative.

How to diagnose U0168

A typical diagnostic flow when this code is present.

  1. 1
    Record all DTCs; pay attention to any B-code security faults stored alongside U0168.
  2. 2
    Check battery voltage and load-test the battery; correct any charging system faults before continuing.
  3. 3
    Verify ignition-on supply voltage and ground at the VSCM connector.
  4. 4
    Inspect the VSCM harness, especially at the steering column entry and firewall grommet.
  5. 5
    Attempt direct scan tool communication with the VSCM to determine if the module is alive on the bus.
  6. 6
    Check for outstanding TSBs or software updates for the security system.
  7. 7
    If the VSCM cannot be reached and wiring is confirmed good, replace the VSCM and perform the manufacturer-specified immobiliser programming sequence with the ECM.

Related network codes

Frequently asked questions

Will U0168 cause a no-start?

Often yes. Because the ECM relies on the VSCM for immobiliser authorisation, most calibrations will prevent starting or will stall the engine when VSCM communication is lost.

Can I bypass the VSCM to get the car running?

Bypassing the immobiliser is outside the scope of OBD-II diagnosis and may be illegal depending on jurisdiction. The correct repair is to restore communication or replace and pair the VSCM.

If I replace the ECM, will U0168 clear on its own?

No. Replacing the ECM without performing the immobiliser pairing procedure will typically set U0168 and prevent starting because the new ECM does not recognise the existing VSCM key codes.

Can a flat key battery cause U0168?

Indirectly. A flat transponder battery in the key fob reduces the signal strength to the VSCM receiver. If the VSCM cannot validate the key it may fault internally, which can result in U0168 being set by the ECM.

Disabling U0168 in software

RaceTune can permanently disable U0168 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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