Communication / Network Path

When this path fits

Use this path when a scan returns one or more U-codes, when several warning lights came on together, or when a scan tool cannot reach a module. If multiple U-codes are stored at once, a shared power, ground, or bus wiring fault is far more likely than several modules failing at the same time.

1. 1Test the battery and charging system. Low voltage is the most common cause of module communication faults.
2. 2Scan every module, not just the engine. Several U-codes together point to one shared power, ground, or bus fault.
3. 3Check the power and ignition fuses for the affected module, and find out what blew any fuse you replace.
4. 4Clean and re-torque the module ground. Corroded or loose grounds create exactly this behaviour.
5. 5Inspect the module connector for corrosion, water staining, and backed-out pins.
6. 6Trace the bus wiring from the module to the gateway and the diagnostic (DLC) connector, looking for chafing, rodent damage, and repairs.

Most likely causes

• Weak or dead battery, or low system voltage
• Corroded or loose module ground
• Damaged or water-intruded connector
• Chafed, broken, or shorted bus wiring
• Blown module power fuse
• Failed module (last, and only after the above are verified)

Inspect-first tools

Relevant parts after inspection