C1A72 — ABS module CAN communication fault

Causes

• Open, short, or intermittent wiring on CAN High or CAN Low between the ABS module and the CAN bus
• Corroded or damaged ABS module connector or pins
• Failed ABS control module
• Faulty gateway, BCM, or other module on the same CAN network
• Missing or damaged termination resistor(s) (open or incorrect resistance)
• Low battery voltage, poor power or ground to the ABS module

Symptoms

• ABS warning lamp illuminated
• Traction control / DSC / ESP warning lights may also be on
• Loss or intermittent loss of ABS and traction control functions
• Related vehicle dynamic systems or dash messages may report communication errors
• Speedometer or other networked modules may show faults or incorrect behavior
• Stored communication fault(s) in ABS and other modules

What to check

• Connect a compatible diagnostic scanner and read all stored and pending codes from ABS and other network modules; note freeze-frame and time stamps
• Check battery voltage (should be stable ~12.5–13.5 V with engine off / >13.5 V with engine running)
• Visually inspect ABS module connector(s) and nearby wiring for corrosion, damage, water ingress or heat damage
• Check fuses and relays related to ABS power and control circuits
• Use a scope or multimeter to measure voltages at the ABS module pins (power, ground, CAN H, CAN L)
• Measure termination resistance between CAN H and CAN L (expected ~60 ohms with ignition on, two 120Ω in parallel)

Signal parameters

• CAN bus idle (recessive) voltage: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (approximately equal)
• CAN bus dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
• Termination resistance between CAN_H and CAN_L: approximately 60 Ω (two 120 Ω terminators in parallel)
• ABS module supply voltage: ~12 V nominal (check for 15 V faults)
• Module ground resistance to chassis:
• CAN bus bit rate: vehicle-specific (commonly 500 kbps or 250 kbps); verify using scope or scan tool

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