C1550 — Replace Electronic Control Unit (ECU)

Causes

• Internal ECU hardware or processor failure
• Corrupted or incompatible ECU software/firmware
• Intermittent or lost power supply to the ECU (battery, fuse, wiring)
• Poor or open ground connections at the ECU
• CAN / LIN bus communication faults or short circuits
• Water ingress, corrosion or physical damage to ECU or connectors

Symptoms

• Malfunction indicator/ABS/traction lights illuminated (depending on module)
• Loss of functions controlled by the affected ECU (brakes/ABS/ESP/steering assists, etc.)
• Intermittent or complete loss of communication with the module on a diagnostic tool
• Vehicle enters limp mode or certain systems disabled
• Unusual error messages or multiple related DTCs stored

What to check

• Read and record all stored DTCs and freeze-frame data with a capable scan tool
• Check battery voltage (resting and cranking) and battery condition
• Inspect fuses and relays related to the module power/ignition circuits
• Visually inspect ECU connectors for water, corrosion, bent pins or damage
• Verify solid ground(s) at the ECU and continuity to chassis
• Check CAN/LIN bus continuity and resistance between CAN H and CAN L

Signal parameters

• Battery/resting voltage: ~12.4–12.8 V (vehicle-specific acceptable range)
• Operating voltage at ECU power pin with ignition ON: ~11–14.5 V
• Ground continuity: near 0 ohms to chassis
• CAN bus idle voltages (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V
• CAN bus dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V
• CAN bus differential resistance between termination resistors: ≈ 60 ohms (two 120 ohm terminators in parallel)

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