BYD Han DM-i Integrated Dual Motor Controller Structure and Fault Diagnosis Guide

Fault Background

The Han DM-i front compartment houses a highly integrated "dual motor controller" assembly: the generator controller, drive motor controller, bidirectional DC, and a power distribution interface are all in one housing. It connects to the traction battery on one side and drives the drive motor and generator on the other, using boost/buck conversion to match battery voltage with motor operating voltage. When this assembly fails, DTCs are distributed among three "roles"—the drive motor controller (FMCU), ISG generator controller, and boost DC. The diagnostic sequence matters: first check the battery, then read and clear codes, then check according to the fault table, and finally replace the assembly. This article organizes the dual motor controller structure, low-voltage connector pinout, diagnostic procedures, and removal/installation points into a field guide.

Dual Motor Controller Assembly: Four-in-One Structure

• The assembly connects to the vehicle via four types of interfaces: high-voltage wiring harness main connector, low-voltage wiring harness main connector, copper busbar connections (three-phase lines), and coolant hose connections (cooling circuit).
• Bus voltage is divided into three platform references: 340–646V (CHCHV), 200–380V (CHCHQ), 240–456V (CHCHS); actual measurements should be based on the battery management system voltage and dual motor controller bus voltage read via VDS.

Low-Voltage Connector Pinout (35-Pin)

The connector front is male; pins 1–12, 13–23, 24–35 are counted from left to right. Main pins are as follows:

• CAN termination resistor: With the connector connected, measure resistance between pins 21–33; standard 54–69Ω (test in OFF mode).

High-Voltage Power-Down Procedure (Before Removal/Service)

1. Power down the vehicle to OFF mode;
2. Disconnect the low-voltage battery negative terminal, wait 5 minutes;
3. Open the front compartment lid and disconnect the DC high-voltage busbar connector at the front compartment electronic control assembly end;
4. Use a voltage measurement tool to confirm the voltage between the disconnected high-voltage busbars is within a safe range (less than 60V DC);
5. Insulate and seal the connector with insulating tape to prevent short circuits and foreign object entry.

Diagnostic Procedure

1. Check the battery: Standard voltage 12–14V; if below 11V, charge or replace first before continuing.
2. Read DTCs: Power to ON mode, connect diagnostic scan tool for terminal diagnostics, read and record all module DTCs.
3. Clear and re-read: Clear all DTCs, power down to OFF mode, wait 3 minutes, then power to ON mode again, read and record again.
4. Refer to the fault diagnostic table: If the symptom is in the table, check according to the corresponding entry; if not, follow the general procedure.
5. After repair or replacement of the dual motor controller, perform a test to confirm.

Typical DTCs and Inspection Points

Common inspection methods:

• Motor body assessment: After removing the controller, measure the motor three-phase resistance separately; the difference between any two phases should not exceed 1Ω, and can be compared with a known-good vehicle.
• IGBT voltage drop method: Set multimeter to diode mode, measure three-phase lines A/B/C to DC bus positive, and DC bus negative to three-phase lines A/B/C for normal voltage drop; impedance between three-phase lines and chassis ground should be in the megohm range (refer to insulation resistance).
• Bus voltage verification: Use VDS to read battery management system voltage and dual motor controller bus voltage, compare with platform references 340–646V / 200–380V / 240–456V.
• Over-temperature faults: First check high-voltage cooling circuit and water pump (oil pump) low-voltage circuit; can read EHS assembly program version info, confirm if DTCs can be cleared, then repeatedly power to OK mode and test drive to see if it recurs; check motor cooling circuit, focusing on motor oil jacket and interfaces, can squeeze hoses to confirm.
• Resolver/phase loss/Hall faults (signal loss, angle anomaly, amplitude reduction, missing A/B/C phase, current Hall A/B fault): First perform motor three-phase resistance assessment; if abnormal, replace motor; if normal, attempt to clear DTCs, if cannot clear, replace dual motor controller (for ISG side, replace EHS assembly accordingly).
• Hardware overcurrent/overvoltage flags, upper/lower arm errors: Power down to OFF mode, check low-voltage wiring harness and low-voltage connector, attempt to clear codes, then power to OK mode and drive to see if it recurs; if recurs, replace dual motor controller.
• EEPROM error: Replace dual motor controller directly.

Removal and Installation Points

Removal sequence: Remove intercooler pipe → Remove dual motor controller DC busbar (M6 bolts) → Remove power distribution wiring harness → Remove power distribution box (M6 bolts) → Remove low-voltage wiring harness → Remove mounting and motor connection studs and bolts (M12 bolts) → Remove dual motor controller inlet and outlet coolant hoses → Remove mating bolts between dual motor controller and dual motors (M12 bolts) → Lift the dual motor controller upward 70mm along the alignment pin direction, then move it to the right to remove.

Installation points:

Safety Warnings

• This article is for technical reference only; high-voltage service must be performed by certified personnel per OEM specifications. Unfamiliar readers are strictly prohibited from performing operations themselves.
• High-voltage work must follow the "supervisor system": designate a dedicated supervisor to monitor the entire process and direct power-on; the worker performs single-handed operations, and in principle, no live work is allowed.
• Power-down sequence must be strictly followed: OFF mode → disconnect low-voltage battery negative → wait 5 minutes → disconnect DC high-voltage busbar connector → confirm <60V.
• Replacement of high-voltage circuit components must use components of the original design capacity; in case of fire, only dry powder extinguishers and dry sand are allowed, water-based extinguishers are strictly prohibited.

Maintenance Insights

The troubleshooting logic for the dual motor controller can be summarized in one sentence: First clarify the "electrical" aspects, then replace the "components" correctly. It packs three power chains—generator, drive motor, and bidirectional DC—into one housing, so DTCs are numbered by "role"—FMCU, ISG, and boost DC each manage a section, but the smallest replacement unit is the entire dual motor controller (for ISG side, replace EHS assembly). Therefore, the two most practical field experiences are: For voltage-type faults, first compare bus voltage references (three platforms 340–646V / 200–380V / 240–456V, first rule out battery pack and BMS issues); For IGBT-type faults, first perform diode-mode voltage drop and three-phase resistance measurements (difference between any two phases ≤1Ω), to distinguish "motor failure vs. controller failure" and avoid replacing a good assembly.

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【This article is for reference only】