BYD Han DM-p High-Voltage Power Distribution Box and DC Charging Power Distribution Box Service Guide

Fault Background

In the Han DM-p, high-voltage DC power is not routed in a single continuous path. Instead, it is distributed by a two-box system: the high-voltage power distribution box (located above the front compartment motor controller) distributes high-voltage DC from the traction battery to the air conditioning system and front PTC heater, with fuses protecting each circuit; the DC charging power distribution box (located under the chassis) uses contactors that open/close each circuit to enable DC charging in this hybrid model, and it includes contactor welding (sintering) detection. The service manual is clear on the repair scope for both boxes: all DTCs are provided by the BMS, and the most common on-site fault is a blown fuse. The only confirmed diagnostic method is: power down the vehicle to OFF, disconnect the 12V battery negative terminal, wait 5 minutes, then open the cover and use a multimeter in continuity mode to test the fuse; if confirmed damaged, replace the entire box under manufacturer guidance. This article compiles the functional division, connector definitions, diagnostic procedures, and torque specifications for both boxes into an on-site guide.

Box Functions and Installation Locations

Memory aid: The front box manages "distribution" (AC + PTC), the chassis box manages "charging" (DC fast charge contactors). Neither box outputs diagnostic codes itself; always read BMS first.

High-Voltage Power Distribution Box: Fuse Inspection and Judgment

High-voltage power distribution box faults typically manifest as blown fuses. Judgment steps (power-off is the first prerequisite):

1. Power down the vehicle to OFF, disconnect the 12V battery negative terminal, wait 5 minutes;
2. Open the front hood, disconnect the dual motor controller busbar connector;
3. Remove the resonator above the high-voltage power distribution box;
4. Open the cover of the high-voltage power distribution box;
5. Set the multimeter to continuity mode, place the probes on both ends of the fuse: continuity indicates normal, no continuity indicates damage.

If the box itself is confirmed faulty, replace the high-voltage power distribution box under manufacturer guidance; do not disassemble or repair internal circuits in the shop.

DC Charging Power Distribution Box: Contactors and Low-Voltage Pins

The core of the DC charging power distribution box assembly is the fast charge positive contactor and fast charge negative contactor, along with contactor welding detection circuitry (to detect if contactors are sintered/stuck). The low-voltage connector pinout on the product side is as follows (compiled from manual section 2.3.4 pin definitions):

The high-voltage side has six connections: DC distribution positive/negative (to battery pack), on-board power supply DC positive/negative (to on-board power supply assembly), DC charge port positive/negative — the complete fast charge current path is "charge port → DC charging power distribution box contactors → battery pack".

Diagnostic Procedure

The standard diagnostic sequence for the DC charging power distribution box (manual sections 2.5/2.6):

1. Bring the vehicle into the service bay, ask the customer about the fault condition and environment (customer-reported fault analysis);
2. Check the starter battery voltage: standard 12–14V — if below 12V, charge or replace the battery first, then proceed to the next step;
3. Refer to the fault symptom table: if the fault is listed → follow the table; if not → proceed to the next step;
4. Comprehensive analysis and diagnosis;
5. Adjust, repair, or replace wiring or components;
6. Verify: after the fault no longer occurs, simulate the conditions and environment of the first fault and test again to confirm it does not reproduce.

Disassembly and Torque

High-Voltage Power Distribution Box Removal (the 3 cover bolts are single-use and must be replaced):

1. Power down vehicle to OFF, disconnect 12V battery negative, wait 5 minutes;
2. Open front hood, disconnect dual motor controller busbar connector; remove resonator;
3. Loosen the 3 cover bolts (discard removed bolts);
4. Unscrew the high-voltage terminal and feed-through connector flange bolts for each circuit inside the box, pull out the feed-through connectors;
5. Use a ratchet to remove the 3 fastening bolts securing the box, then remove the box;
6. Reinstall the cover with 6 bolts.

High-Voltage Power Distribution Box Installation: Wear insulating gloves → position the new box and secure with 3 M6 fastening bolts → align and insert the load-side high-voltage feed-through connectors, secure the terminals with 6 M5 bolts → secure the feed-through connector flanges with 3 M6 bolts → secure the cover with 6 M6 bolts, tighten per torque table → reinstall the resonator and dual motor controller busbar connector (all fasteners meet corresponding torque requirements).

DC Charging Power Distribution Box Removal: Power down to OFF → disconnect 12V battery negative → wait 5 minutes → lift the vehicle, remove the box protective cover → first disconnect the rear high-voltage wiring harness battery pack connector, then unplug the low-voltage connector and cable ties → loosen the 8 M6 bolts on the cover and remove it → loosen the 4 M8 bolts securing the high-voltage cable lugs and the 2 M6 bolts securing the IPT, unplug the IPT connector → loosen the 3 M6 nuts securing the box, then remove the box. Installation is the reverse order.

• Fastener torque: M5 hex flange bolts, M6 hex flange bolts, M8 bolts per manual torque table;
• Tools: wrench set (150-piece), torque wrench, 1000V insulating gloves (for high-voltage box removal);
• General requirements: wear gloves to prevent injury; always wear insulating gloves when connecting/disconnecting high-voltage connectors, and protect male/female terminals with insulating tape; ensure the assembly is clean and free of scratches before installation.

Safety Warnings

• This article is for technical reference only; high-voltage component service must be performed by certified personnel per OEM specifications. Unfamiliar readers must not attempt any operation.
• Before any cover removal or disassembly, power down vehicle to OFF → disconnect 12V battery negative → wait 5 minutes — all steps are mandatory.
• The high-voltage power distribution box cover bolts are single-use; discard after removal, and must be replaced with new ones and torqued to spec during reassembly.
• Always wear insulating gloves when connecting/disconnecting high-voltage connectors, and protect male/female terminals with insulating tape to prevent foreign objects and short circuits.
• Replacement of both boxes must be done under manufacturer guidance; do not repair contactors or fuse circuits inside the boxes in the shop.

Service Insights

The most valuable part of this manual is the three "on-site disciplines." First, the 5-minute wait is not optional — after powering down and disconnecting the 12V battery negative, you must wait a full 5 minutes before opening the cover; this is the minimum time for high-voltage circuit discharge, and skipping it is equivalent to working live. Second, the starter battery is the first gate for charging faults — before diagnosing the DC charging box, measure the starter battery; standard is 12–14V; if below 12V, charge or replace the battery first. Skipping this step may make all subsequent "charging faults" appear as false positives. Third, after repair, you must "simulate and retest" — the fault disappearing is not the end; you must recreate the conditions and environment of the original fault and test again, specifically to catch intermittent and poor-contact faults. Combined with the rule that "DTCs are provided by the BMS," the on-site logic is closed: read BMS → measure starter battery → power down, wait 5 minutes, open cover, test fuse → replace box under manufacturer guidance → simulate and retest.

---

【This article is for reference only】