C1025 — CAN Communication BAS communication with ESP control unit faulty

Causes

• Open, short or intermittent wiring on the CAN bus between BAS and ESP
• Poor connector contact or corrosion at BAS, ESP or junctions
• Failed BAS module
• Failed ESP control unit
• Missing or incorrect CAN termination (open/multiple terminators)
• Low battery voltage or poor ground affecting module communication

Symptoms

• BAS, ESP and/or ABS warning lamp illuminated
• Brake assist functions reduced or disabled (harder pedal effort)
• Traction control/ESP functions reduced or disabled
• Multiple communication-related DTCs stored
• Intermittent or permanent loss of ABS/ESP functionality
• Possible driveability complaints related to safety system interventions

What to check

• Read and record all stored DTCs and freeze-frame data from all modules (BAS, ESP, ABS, gateway).
• Check battery voltage and charge state; verify good battery terminals and chassis ground.
• Visually inspect harnesses and connectors at BAS and ESP for corrosion, water ingress, bent pins or damage.
• Scan the CAN bus: confirm presence of BAS and ESP nodes and check for additional U/C codes.
• Measure CAN‑High and CAN‑Low voltages at the BAS and ESP connectors with ignition on.
• Measure resistance across CAN H to CAN L with ignition off (termination check).

Signal parameters

• Typical idle voltages: CAN High ≈ 2.5 V, CAN Low ≈ 2.5 V (each to chassis).
• Dominant state: CAN High ≈ 3.5 V, CAN Low ≈ 1.5 V (differential ≈ 2.0 V).
• Differential voltage (CAN H - CAN L) idle ≈ 0 V; dominant ≈ 2.0 V.
• Termination resistance between CAN H and CAN L ≈ 60 ohms (two 120 Ω terminators in parallel).
• Typical CAN baud rates on Mercedes systems are 250 kbps or 500 kbps — verify for the specific vehicle.

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