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Home / DTC / C1025 — CAN Communication BAS communication with ESP control unit faulty

C1025 — CAN Communication BAS communication with ESP control unit faulty

Detailed page for trouble code C1025.

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Code

C1025

MERCEDES-BENZ C — Chassis

CAN Communication BAS communication with ESP control unit faulty

Brand: MERCEDES-BENZ
Type: C — Chassis
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Page language: EN

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.

Diagnostic algorithm

  1. Record all DTCs from all control units and note any related U-codes or additional C-codes.
  2. Verify battery voltage ≥ 12.4 V (engine off) and charging system operation. Repair charging/ground issues first.
  3. Visually inspect BAS and ESP connectors and harness routing; repair any damage, corrosion or pin issues.
  4. With ignition ON, measure CAN H and CAN L at BAS and ESP connectors and compare to expected signal parameters.
  5. With ignition OFF, measure resistance between CAN H and CAN L at a convenient splice to confirm ≈ 60 Ω. If open or wrong, trace wiring for open/short.
  6. Perform continuity and short-to-power/ground checks on CAN wires between BAS and ESP. Repair any short or open.
  7. If wiring and termination are correct, disconnect the BAS module and check whether the bus behaves differently (some modules can hold bus in a dominant state).
  8. Swap or replace with a known-good BAS or ESP module only after confirming wiring and power/ground integrity and after obtaining OEM reprogramming procedures if required.
  9. After repairs, clear codes and perform road test/validated communication checks. If code returns, escalate to module bench testing or dealer-level diagnostics with manufacturer tools.

Likely causes

  • Damaged/loose connector at BAS or ESP
  • CAN bus short to battery or ground between BAS and ESP
  • Failed BAS module
  • Faulty ground or low supply voltage to BAS or ESP

Fault status

⚠️ Status
CAN communication fault: BAS control unit not communicating correctly with ESP control unit. Safety-related functions may be reduced.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5-3.0 hours

Similar codes

C1023 C1024 U0121 U0100 C1030
856

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