BYD Seal Complete Vehicle Leakage Diagnosis and High-Voltage Wiring Harness Pinout Guide

Fault Background

The Seal's complete vehicle high-voltage system leakage diagnosis follows a standardized OEM process: software first, then power-down, then per-load insulation testing, and finally precise calculation of the traction battery pack insulation resistance using the "voltage method + parallel resistance method." Meanwhile, the complete vehicle high-voltage wiring harness starts from the charge port on the right rear side panel, runs along a fixed path to the rear drive electric assembly, and each low-voltage pin of the charge port has a clear destination. This article compiles both parts into a field guide—complete leakage diagnosis steps, judgment thresholds, tool requirements, and high-voltage wiring harness layout and pin definitions.

Leakage Diagnosis: Tools and Operation Requirements

Complete Vehicle High-Voltage Load Insulation Testing Steps

1. Software first: Use VDS to confirm the leakage sensor software is the latest version; if the leakage DTC persists after update, power down to OFF and wait 5 minutes.
2. Standard power-down: Wear insulating gloves, first disconnect the low-voltage battery positive terminal → disconnect the air conditioning high-voltage connector → disconnect the traction battery high-voltage output connector → only proceed if the multimeter measures the harness end voltage ≤60V.
3. Per-load insulation test: Use the insulation resistance tester to measure the insulation resistance of each air conditioning component's positive terminal to ground and negative terminal to ground, uniformly using the DC 500V range. If the nameplate traction battery rated voltage is greater than 436V, use a range not lower than and closest to the battery pack maximum voltage; the battery pack maximum working voltage is estimated as 1.15 times the nameplate rated voltage.
4. Judgment and expansion: If any component's resistance is <2MΩ, it is judged as leaking; if normal, sequentially disconnect other high-voltage loads and test each with the same method; after all high-voltage loads on the three-in-one are disconnected, measure the insulation of all its high-voltage connector terminals (positive/negative) to ground; finally, test the DC charge port and AC charge port insulation in sequence.

Battery Pack Insulation Resistance Testing Steps

1. Disconnect high-voltage connectors, and according to the battery connector pin definitions, energize all high-voltage contactors inside the battery pack (except the precharge contactor)—connect the 12V battery positive to the contactor supply pin and negative to the control pin, wearing insulating gloves throughout; then measure the battery pack total voltage to confirm all contactors are energized.
2. Use two multimeters to measure negative terminal to body ground voltage V⁻ and positive terminal to body ground voltage V⁺ respectively, and record.
3. On the side with lower voltage (corresponding to the smaller of V⁺ and V⁻), connect a known resistance R (recommended 1MΩ) in parallel between that side and ground, take a third voltage measurement, and record as V.
4. Calculate the insulation resistance Ri2 using the formula (note: the result is the parallel combination of the minimum insulation resistance and the multimeter internal resistance).
5. Judgment: Divide Ri2 by the battery pack maximum working voltage; the result must not be less than 500Ω/V, otherwise the battery pack is judged as leaking.

High-Voltage Wiring Harness Assembly: Layout and Pins

• Layout path: The AC/DC combo charge port is located on the vehicle's right rear side panel; the harness runs sequentially through the right rear wheel house inner panel, right rear longitudinal member, rear floor, and rear subframe mounting points, finally forming electrical connections with the rear drive electric assembly via DC cable lugs and AC connector; there is also a branch from the right rear wheel house inner panel opening routed to the middle floor rear section, providing the in-vehicle discharge input connector (rear-drive/four-wheel-drive layouts differ slightly).
• AC charge port low-voltage pin definitions:

Key Parameters Quick Reference

Safety Warnings

• This article is for technical reference; high-voltage insulation testing must be performed by certified personnel per OEM specifications; readers unfamiliar with the procedures are strictly prohibited from performing operations themselves.
• Wear qualified insulating equipment (≥1kV) throughout; one operator with one supervisor; isolate the area and post warning signs.
• Strictly follow the power-down sequence: first low-voltage battery positive terminal → then high-voltage connectors; before measurement, confirm the harness end voltage is ≤60V.
• Energizing battery pack contactors for testing is a special operation; it must be performed according to pin definitions and with insulating gloves, and restore to original state after completion.

Maintenance Insights

The Seal's leakage diagnosis process has two clever aspects: first, the "2MΩ and 500Ω/V dual thresholds"—the load side uses an absolute resistance of 2MΩ for quick screening, while the battery pack side uses "resistance divided by maximum working voltage ≥500Ω/V" for normalized judgment; the former governs components, the latter governs the battery pack, and they cannot be mixed; second, the "parallel known resistance to obtain true insulation"—the multimeter internal resistance is only on the order of 10MΩ, so directly measuring high-voltage insulation will be "pulled down" by the internal resistance; by paralleling a 1MΩ resistor and taking three measurements before applying the formula, a credible insulation value can be obtained. Also, do not overlook the first step of the process: update the leakage sensor software first—many "leakage" cases are actually false alarms from old software versions.

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【This article is for reference only】