U0603

Lost Communication With Navigation Control Module

U0603 is a generic OBD-II network diagnostic trouble code: Lost Communication With Navigation 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
U0603
Group
Network
System
Network
Severity
Information only
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What U0603 means

U0603 is stored when the gateway or BCM loses all network communication with the Navigation Control Module (NCM). The NCM provides route guidance, map data, and in some architectures also processes GPS positioning data used by other modules such as the telematics unit or the vehicle's time-and-date synchronization function. Loss of the NCM does not affect powertrain or safety systems.

Because the navigation module often shares a high-speed CAN or MOST bus with the infotainment head unit, this code can appear alongside codes for audio, telephone, and display modules when the entire infotainment bus segment fails. Alternatively, U0603 may appear in isolation when only the navigation module has an internal fault or connector problem.

This is a comfort and convenience fault. The vehicle remains fully driveable and all safety-critical systems continue to operate normally. Diagnosis should start with verifying power, ground, and bus connectivity at the NCM before considering replacement, as infotainment modules are frequently prone to connector issues due to limited airflow and thermal cycling in the dashboard environment.

Common causes

Most-frequently reported root causes when U0603 is logged.

  • 1
    Failed Navigation Control Module.
  • 2
    Loss of power or ground supply to the NCM.
  • 3
    Open or short circuit on the CAN, MOST, or proprietary bus wiring to the NCM.
  • 4
    Corroded or damaged connector at the NCM behind the dashboard.
  • 5
    Software crash or unrecoverable firmware fault within the NCM.
  • 6
    Loose or unseated harness connector due to vibration or previous service work.
  • 7
    Blown fuse for the infotainment or navigation module circuit.

Symptoms drivers notice

Navigation and map functions completely unavailable.
Navigation display may be blank or show an error message.
GPS-based features such as time sync or telematics may also be disrupted.
U0603 stored in the BCM or infotainment gateway.
Companion infotainment codes may be present if the full bus segment is affected.

How to diagnose U0603

A typical diagnostic flow when this code is present.

  1. 1
    Read all stored DTCs and identify whether multiple infotainment codes are present or only U0603.
  2. 2
    Check the fuse for the navigation or infotainment module supply circuit.
  3. 3
    Verify power and ground at the NCM connector.
  4. 4
    Inspect the NCM harness connector for seating, corrosion, or damaged terminals.
  5. 5
    Attempt a hard reset by disconnecting NCM power for a minimum of two minutes.
  6. 6
    Check bus wiring between the head unit and NCM for continuity and insulation integrity.
  7. 7
    Replace or reprogram the NCM if all wiring and power checks pass and the module does not recover.

Related network codes

Frequently asked questions

Is it safe to drive with U0603?

Yes. U0603 is a comfort fault; all powertrain and safety systems are unaffected.

Can a software update cause U0603?

Yes. A failed or interrupted firmware update to the NCM can leave it in an unresponsive state, triggering a lost-communication code.

Will disconnecting the battery reset U0603?

A battery disconnect may temporarily clear the stored code, but if the NCM has an internal fault the code will return when the module fails to communicate again.

Could U0603 affect automatic time and date on the dashboard?

Yes, on vehicles where the clock is synchronized to GPS time via the NCM, loss of the navigation module can cause the clock to revert to a default or last-known time.

Disabling U0603 in software

RaceTune can permanently disable U0603 — 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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