U0146 — Lost Communication With Serial Data Gateway Module A

Causes

• Open or short in CAN/serial data wiring or connectors
• Faulty Serial Data Gateway Module A (SDGM-A)
• Blown fuse or loss of module power/ground
• Network bus off condition or missing termination
• Software/firmware error or module needing a reflash
• Aftermarket device or accessory interfering with the bus

Symptoms

• One or more warning lamps (check engine, ABS, airbag, etc.)
• Loss of multiple vehicle functions that rely on networked modules
• Intermittent or permanent loss of instrument cluster messages
• Unresponsive vehicle features (doors, HVAC, telematics)
• Diagnostic scanner cannot communicate with the gateway module

What to check

• Check battery voltage (should be >12.4 V with key off and >13.0 V with engine running)
• Inspect fuses related to gateway and network power/IGN circuits
• Visually inspect connector pins at the gateway and nearby junctions for corrosion or bent pins
• Use a scan tool to list modules and note which modules are missing or reporting U-codes
• Check for aftermarket modules or recent wiring work that could affect the bus
• Quickly measure CAN bus idle voltages with vehicle key on (see signal_params)

Signal parameters

• CAN high (recessive): approx. 2.4–2.6 V
• CAN low (recessive): approx. 2.4–2.6 V
• CAN high (dominant): approx. 3.5–3.7 V; CAN low (dominant): approx. 1.3–1.5 V
• CAN differential (dominant): approx. 1.8–2.5 V
• Termination resistance (two terminators in parallel): approx. 60 Ω across CANH–CANL
• Common bus data rates: 125 kbps, 250 kbps, 500 kbps (verify vehicle-specific rate with factory data)

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