U0303 — Software Incompatibility With Transfer Case Control Module

U0303 identifies software incompatibility involving the transfer-case control module. It does not, on its own, indicate a mechanical transfer-case defect or a loss of communication; vehicle-specific software and module information is needed.

Affected system: Network communication

Symptoms

• System warning may illuminate
• Affected feature may be unavailable
• Symptoms depend on the vehicle

Possible causes

• Module power or ground loss, connector or network wiring fault, or a module that stopped communicating
• Module power, ground, or connector fault
• Vehicle-specific mechanical or control issue

What to check

• Record all available module faults
• Scan all accessible modules and record which modules report the communication fault. Check battery voltage, module power and ground, connectors, and network wiring using the vehicle topology.
• Compare results with vehicle-specific service information
• Verify the repair
• Scan all accessible modules and record which modules report the communication fault. Check battery voltage, module power and ground, connectors, and network wiring using the vehicle topology.
• Repair the verified cause and rescan all affected modules

Also written as: U0303-00, U030300, UO303 (some scan tools add the fault-type byte, e.g. -00).