U2108 — CAN-Bus no Communication with ABS/TC

Causes

• Lost or intermittent power or ground to the ABS/TC module
• Open, short or high-resistance wiring on CAN High (CANH) or CAN Low (CANL) lines
• Disconnected, corroded or damaged ABS/TC module connector(s)
• Missing or incorrect termination (open or shorted 120 Ω resistors) on the CAN bus
• Short to battery or ground on CAN lines
• Faulty ABS/TC control module

Symptoms

• ABS and/or TC warning lamp illuminated
• Loss of ABS/traction control functions (no ABS pumping on heavy braking)
• ABS/TC module not present or not responding on a diagnostic scanner
• Related warning lamps (brake, stability control) or degraded mode messages
• Possible loss of vehicle stability functions during cornering or slippery conditions
• Possible CAN bus related errors or multiple network communication DTCs present

What to check

• Connect a dealer-level or capable OBD2 scan tool and read stored and pending codes from all network modules (ABS, BCM, engine, gateway)
• Confirm whether ABS/TC module is detected by the scanner and whether it reports internal faults
• Visually inspect ABS module connector, wiring harness at module and along routing for damage, corrosion or water entry
• Check ABS module power and ground pins for battery voltage (ignition ON) and a good ground (low resistance to chassis)
• Check fuses and relays for ABS and CAN power circuits
• Measure resistance between CANH and CANL with ignition OFF — expected ~60 Ω (two 120 Ω terminators in parallel)

Signal parameters

• Idle voltages (key ON, bus idle): CANH ≈ 2.5 V, CANL ≈ 2.5 V
• Dominant state voltages during traffic: CANH ≈ 3.5 V, CANL ≈ 1.5 V (differential ≈ 2.0 V)
• Termination resistance end-to-end (whole bus): ≈ 60 Ω (two 120 Ω terminators in parallel)
• Typical bus baud rates (depends on network): commonly 500 kbps or 250 kbps (verify vehicle-specific)
• Supply voltage for module power: vehicle battery nominal 12 V (should be stable 11–15 V during checks)

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