AU
B1788-00

Professional verification confirms BYD and standard OBD-II systems define DTC B1788-00 as "Mirror Passenger Down Circuit Short To Battery," rather than the airbag fault stated in the original information — Atto 8

Safety System

Professional verification confirms BYD and standard OBD-II systems define DTC B1788-00 as "Mirror Passenger Down Circuit Short To Battery," rather than the airbag fault stated in the original information.

This fault code falls under the Body System.

It indicates the Body Control Module (BCM) detects an abnormal short circuit between the passenger-side exterior mirror downward adjustment drive circuit and the vehicle power supply positive terminal (+B).

This fault has the following consequences: 1) The BCM activates its protection mechanism and cuts off circuit output, disabling the mirror downward adjustment function. 2) A sustained short circuit can burn out the internal BCM driver chip or blow the related fuse. 3) Fluctuating short-circuit current can trigger unintended operations, such as the mirror automatically tilting downward after locking the vehicle.

Dual-stage airbag system fault codes typically fall within the B10xx-B13xx range.

Always refer to the actual scan tool reading.

The B1788-00 fault code on the Atto 8 indicates a high-severity short to battery in the passenger-side exterior mirror downward adjustment circuit, detected by the BCM. This can disable mirror down movement and may damage the BCM driver or fuse. Common causes include chafed wiring in the passenger door hinge harness or a shorted mirror adjustment motor. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from 3 recorded cases.
3
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Aged and damaged front passenger-side door wiring harness sleeve causes the door mirror power wire and downward adjustment signal wire to chafe and short together (common location: inside the wiring harness sleeve at the door hinge).
  • 2Burned internal coil insulation in the door mirror adjustment motor causes a short circuit between the positive and negative terminals, resulting in abnormally low resistance (normal: 15-25Ω; close to 0Ω when short-circuited).
  • 3Installing an aftermarket door mirror assembly with an internal circuit pinout or resistance value that does not match the genuine part causes the BCM to incorrectly detect a short to power.
  • 4Body Control Module (BCM) internal driver circuit fault: MOSFET breakdown causes continuous high level at output terminal.
  • 5Vehicle wading or poor door sealing allows water to enter and corrode the door mirror connector, creating a short circuit between the pins.
What To Do
  • 1
    Disconnect the battery negative terminal and wait 3 minutes to discharge the residual charge in the BCM capacitor and reset the diagnostic system.
  • 2
    Remove the front passenger door trim panel. Carefully inspect the wiring harness sleeve at the door-to-body connection. Pull back the corrugated conduit and inspect the wire insulation for wear. Repair any damaged wiring and rewrap the harness.
  • 3
    Disconnect the door mirror connector. Use a multimeter to measure the resistance between the "down adjustment" pin and the positive power supply. If the resistance is less than 5Ω, the wiring has a short circuit. Measure the motor resistance. If it falls outside the standard value (15-25Ω), replace the door mirror assembly.
  • 4
    Check BCM output: Connect the diagnostic tool and read the data stream. Observe the BCM output voltage while operating the downward adjustment. A 12V output without operation indicates an internal BCM fault.
  • 5
    After repairing the short circuit source, clear the fault code and perform rearview mirror position initialization learning (on some models, use VDS to execute the "Exterior Rearview Mirror Memory Learning" function). Verify that adjustment in all directions and the memory function operate normally.
Real-World Cases
BYD DTC AI Analysis

BYD S6 - Door wiring harness protective sleeve wear causes short circuit

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Symptoms: Passenger mirror would not adjust downward; other directions normal. DTC B1788-00. Diagnosis: Removed right front door panel. Wiring harness boot at door hinge was torn. Brown (down adjustment signal) and red (power +) wire insulation worn through, causing a short. Repair: Cut damaged sections, re-soldered, and insulated with heat-shrink tubing. Rerouted harness to avoid interference. Cleared DTC; function restored.
BYD DTC AI Analysis

BYD Tang DM – Side mirror motor internal short circuit

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Symptoms: After locking, the passenger-side mirror automatically tilted down (reverse tilt malfunction). DTC B1788-00 stored and would not clear. Diagnosis: Disconnected the mirror connector; the short disappeared. Measured resistance between the motor down-adjust winding and housing at 0.8Ω (should be infinite). Confirmed the internal motor coil burned and shorted. Solution: Replaced the OEM passenger-side mirror assembly (with memory module). Performed "mirror position learning" and "seat memory matching" using VDS. Fault eliminated.
BYD DTC AI Analysis

BYD Song Pro - Aftermarket Parts Incompatibility

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Symptom: Aftermarket passenger-side mirror installed following accident. DTC B1788-00 sets and returns immediately after clearing. Diagnosis: Pin definitions matched between genuine and aftermarket parts, but the downward adjustment circuit on the aftermarket unit measured only 3Ω (versus 18Ω genuine). Internal diode reverse leakage current caused the BCM to falsely detect a short to power. Repair: Installed a genuine certified mirror and performed BCM coding configuration using VDS. Fault code cleared.
Other Atto 8 Fault Codes
B110811This DTC indicates a short circuit in the air conditioning system PM2.5 air quality sensor (rapid detector). Specifically, abnormal continuity exists between the sensor power supply circuit or signal output circuit and body ground or battery positive. This causes the control module (ACU/air conditioning controller) to detect abnormal current or a voltage signal outside the valid range (typically 0V or supply voltage). The PM2.5 sensor monitors internal and external particulate concentrations, providing the data the automatic air conditioning system uses to switch between fresh air and recirculation modes. A short circuit disables the air quality monitoring function. This fault may force the air conditioning system into recirculation protection mode and trigger related thermal management system faults, as the air conditioning system acts as a key actuator in vehicle thermal management. In severe cases, the short circuit current can damage the internal sampling circuit of the air conditioning controller or overheat the wiring harness.B1109DTC B1109 indicates an open circuit in the communication line between the air conditioning system PM2.5 air quality sensor (dust concentration sensor) and the air conditioning control unit (AC ECU), or an open circuit within the sensor internal circuitry. Typically located in the air conditioning intake duct, this sensor monitors real-time PM2.5 particle concentration inside and outside the vehicle. It provides data to the automatic air conditioning system for intelligent switching between fresh air and recirculation modes and for controlling the air purification device. During an open circuit fault, the AC ECU cannot receive the air quality signal, triggering the system fail-safe mode. Symptoms typically include failure of the automatic recirculation function, abnormal air purification indicator light operation, or abnormal air quality data displayed on the air conditioning panel. Severe cases may compromise the cabin environment control strategy, but do not directly affect vehicle driving safety.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 overview →
Data confidence: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.