BYD Seal AC Driver Cold / Passenger Hot: Air Mix Door Motor Power Supply Wiring Diagnosis

Fault Background

The Seal is equipped with dual-zone automatic climate control, where the left and right vent temperatures are independently regulated by their respective air mix doors. When one side's "air mix (blend) door motor" loses power, the door stops at the wrong position, causing one side to blow cold air and the other hot air. This article breaks down a repair case of "driver cold, passenger hot"—starting from the DTC, but ultimately finding the break in the wiring harness, without blindly replacing any major components.

Fault Symptom

Cause Analysis

1. Passenger air mix door motor fault—motor stuck or burnt, unable to drive the door.
2. Right domain controller fault—controller not outputting drive signal.
3. Wiring fault—motor power or feedback line open circuit, intermittent connection.

Diagnostic Procedure

1. Basic data confirmation: No updates or targeted flashing tasks for VCU, left domain controller, or right domain controller—rule out software factors first.
2. Quantify the symptom: Insert thermometer into vents, measure driver 11.8 °C, passenger 35.9 °C; read heat pump live data from right domain controller, passenger air mix door motor position percentage 0% (abnormal).
3. Refrigeration system verification: Evaporator temperature 1 °C, compressor operating data normal, refrigerant sufficient—cooling capacity is fine, issue is only on passenger side air door.
4. Component swap test: Remove passenger glove box, swap passenger air mix door motor, fault persists, motor position still 0%—motor itself ruled out.
5. Controller swap test: Suspect right domain controller, swap right domain controller, fault persists—controller also ruled out.
6. Wiring measurement: Refer to wiring diagram, measure motor power supply 1 (G103-1 pin) to ground voltage 0 V (abnormal), motor power supply 2 (G103-2 pin) to ground voltage 0 V (abnormal); while passenger air mix door motor feedback power input to ground 5 V (normal), feedback power output also normal—motor is missing "drive power".
7. Continuity localization: Measure motor power supply 1 G103-1 pin to G86F-3 pin harness resistance 0.29 Ω (continuous); motor power supply 2 G103-2 pin to G86F-18 pin not continuous (abnormal)—power supply 2 branch open, break point locked inside harness.
8. Repair verification: Replace relevant wiring harness, passenger air mix door motor returns to normal operation, left and right vent temperatures consistent, fault resolved.

Repair Plan

1. Perform component swap tests (motor, controller) first, use elimination method to narrow down scope, avoid blind part replacement.
2. Refer to wiring diagram, first measure motor power and feedback voltage (distinguish "missing power" vs "missing feedback"), then do resistance continuity measurement to precisely locate open branch.
3. After confirming internal harness open, replace corresponding harness, avoid temporary "splice a wire" fixes.
4. After repair, measure left and right vent temperatures, observe motor position live data 0%→normal range, and perform HVAC self-learning/initialization (if required by vehicle model).

Key Parameter Quick Reference

Safety Warnings

• When inspecting HVAC air door area, be cautious of sharp metal brackets and duct edges inside dashboard to prevent cuts.
• Before measuring harness continuity, ensure complete vehicle power-down to avoid damaging measurement equipment or triggering controller protection.
• When replacing harness, ensure all connectors are fully locked to prevent secondary intermittent connection from driving vibration.

Repair Insights

"Motor not moving" is most easily attributed to the motor itself, but this case used two swap tests to rule out both motor and controller, finally finding the break in the harness. Three key points: First, quantify before acting—the measured 11.8 °C and 35.9 °C from both vents is far more convincing than a vague "passenger blows hot"; Second, voltage first, resistance follows—first measure power to ground voltage to find "missing power", then use continuity measurement to lock the break to specific pins; Third, dare to use swap tests—on low-voltage actuators (excluding high-voltage components), swap testing is the fastest and most economical elimination method.

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【This article is for reference only】