BYD Han DM-p Vehicle Control Unit (VCU) Diagnosis and Replacement Guide

Fault Background

The Han DM-p's Vehicle Control Unit (VCU) module is located under the driver's seat. It handles real-time powertrain calculation and distribution, information exchange and centralized forwarding, sensor signal acquisition and processing, CAN communication, fault alarm and handling, program updates, and self-diagnostics. The service manual defines a clear diagnostic procedure: the low-voltage battery voltage is the overall threshold (standard 11–14V), followed by using the VDS2000 to follow the standard chain of "module detected → check power and ground pins → troubleshoot by DTC". Before replacing the VCU, the anti-theft key must be disarmed using VDS2000; after installation, the key must be re-armed. The fixing nut torque is 7+1 N·m. The DTC table covers 71 codes—from accelerator pedal signals, water pump series (short to ground/power, open circuit, overcurrent, overvoltage, overtemperature, stall), electronic thermostat, clutch and main pressure valves, vacuum pump relay, to BMS/leakage/IPB/front and rear motor systems. This article organizes the functions, pinouts, diagnostic procedures, DTCs, and replacement specifications into a field guide.

System Function and Location

Connector Pin Highlights

The VCU product-side connector is 64-pin and 48-pin (A/B rows). Commonly used pins for field diagnostics:

• Power/Wake-up: B8 (battery positive), B29 (digital input, VCU hardwired wake-up signal), B31 (battery ground), two protected battery supply pins (VCU power driver supply);
• CAN: Two 500 kbps CAN buses, with built-in 120Ω termination resistors; A20 (communication CAN2H, no termination resistor); B18 (half-bridge power, 500 kbps);
• Accelerator Pedal: A52 (sensor 1 power, to pedal pin 3), A53 (sensor 2 power, to pin 6), A35 (sensor 1 ground, to pin 5), A34 (sensor 2 ground), A64 (pedal shield ground), analog input (sensor 1 position signal);
• Coolant Pump Control: A58 (frequency input, electric coolant pump PWM signal feedback), B23 (low-side output, electric coolant pump PWM control, to pump pin 3), engine water pump LIN interface, B-row low-side output (engine water pump PWM control);
• Cooling Fan: B5? (high-side output, cooling fan enable control, to fan pin 1), B24 (low-side output, cooling fan PWM control);
• Hydraulic/Clutch: B16 (half-bridge output, clutch pressure valve), B17 (main pressure solenoid valve), B28 (sub-cool protection solenoid valve), B27 (low-side output, canister purge valve control), plus power and ground pins for main pressure/oil temperature/fuel tank pressure/clutch pressure sensors.

Diagnostic Procedure

1. Bring the vehicle into the service bay.
2. Check low-voltage battery voltage: standard 11–14V—if out of range, refer to the low-voltage battery service manual first; only proceed if within range.
3. Connect VDS2000 to the diagnostic port and read codes. Note: If a communication error occurs, it may be a diagnostic port or VDS2000 issue—connect the VDS2000 to another vehicle to test: if it displays, the original vehicle's diagnostic port is faulty (check port power and hardware); if it does not display, the VDS2000 itself is faulty.
4. Module detected? If not detected, go to step 8 to replace the VCU and rescan.
5. With ignition ON, check VCU harness-side pins B8, A2, A4, B29 for voltage (11–14V).
6. Check harness-side pins A7, A8, B31 for continuity to ground.
7. If power distribution checks are abnormal, inspect the corresponding harness or replace the fuse; after restoring normal operation, rescan with VDS. If normal, proceed with DTC-based troubleshooting.
8. Replace the VCU → rescan with VDS → return to step 1.
9. Confirm the test.

Collision-specific procedure: Has the vehicle been in a collision? If yes, follow the collision procedure. If no, clear the VCU DTCs using VDS.

DTC Table (Typical Codes from 71)

Replacement Specifications (Including Anti-theft Key)

Four preparations before removal:

1. Disarm the anti-theft key using VDS2000.
2. Set ignition switch to OFF.
3. Disconnect the low-voltage battery.
4. Remove the driver's seat.

Removal: Disconnect the VCU low-voltage connectors → loosen and remove the retaining nuts in diagonal order → remove the VCU.

Installation: Position the VCU over the mounting holes → tighten the nuts at positions 1 and 2 to the specified torque (7+1 N·m) → install the low-voltage connectors → re-arm the anti-theft key.

Safety Warnings

• This article is for technical reference only. VCU service must be performed by certified personnel following the OEM manual. Unfamiliar readers must not attempt any operation.
• VCU replacement must complete the full sequence: "disarm anti-theft key → power down and work → re-arm anti-theft key after reassembly". Missing any step will prevent the vehicle from starting or trigger the anti-theft alarm.
• Before removal, the ignition must be OFF and the low-voltage battery disconnected. Supply pin checks are performed with ignition ON; take personal safety precautions.
• Loosen/tighten the retaining nuts in diagonal order, torque 7+1 N·m, to prevent deformation of the mounting feet.

Repair Insights

Three field disciplines worth copying from this VCU manual. First, "voltage before module"—diagnosis starts with the 11–14V battery voltage; with ignition ON, measure supply pins B8/A2/A4/B29 and ground continuity on A7/A8/B31; if power distribution fails, check the harness and replace fuses before replacing the VCU. Second, "VDS2000 cross-vehicle test"—when a communication error occurs, connect the tool to another vehicle and test once: if it displays, the original vehicle's diagnostic port is faulty; if not, the tool is faulty. This immediately identifies the responsible side. Third, "anti-theft key closed loop"—VCU replacement is not just mechanical: disarm the key before removal and re-arm after installation; this is the most easily missed and most consequential step. For DTCs, remember two series: the water pump codes, a group of 12 with the seven-code pattern "short to ground/short to power/open circuit/overcurrent/overvoltage/overtemperature/stall" (engine water pump P2B54xx, electric water pump P2B55xx)—when you see the seven-code pattern, first test the pump wiring and fuses; the vacuum pump P1D8xxx series—when relay faults are reported, check the relay first before suspecting the pump body.

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【This article is for reference only】