AU
C102A00

DTC C102A00 indicates the IPB (Integrated Power Brake) control unit detects an invalid or abnormal reverse gear signal — Seal U

Braking System

DTC C102A00 indicates the IPB (Integrated Power Brake) control unit detects an invalid or abnormal reverse gear signal.

In BYD DM-i and e-Platform 3.0 models, the gearshift controller (or TCU) typically sends the reverse gear signal to the IPB system via the CAN bus.

This signal activates reverse-related brake control strategies, such as reverse automatic hold release logic, reverse misapplication prevention (R-AEB), and hill reverse assist control.

The IPB triggers this fault code if it fails to receive a valid reverse gear signal within a predetermined time, if the received signal contradicts actual vehicle state logic (e.g., vehicle speed conflicts with the reverse gear signal), or if the signal voltage or message format falls outside the valid range.

This fault may prevent the automatic hold system from releasing normally during reverse maneuvers, cause abnormal brake pedal feel, or trigger the brake system degraded protection mode, compromising reversing safety.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Defective IPB control unit software version or abnormal calibration data (signal parsing algorithm error)
  • 2CAN communication fault between the shift actuator controller (or TCU) and the IPB (wiring open circuit, short circuit, or abnormal terminating resistance).
  • 3Reverse signal hardwire connection fault (for some early models or specific configurations, including wiring open circuit, short to ground, or short to power)
  • 4IPB internal signal sampling circuit hardware fault (damaged input interface circuit)
  • 5Vehicle 12V low-voltage power supply system fault (voltage fluctuations cause IPB signal acquisition distortion)
What To Do
  • 1
    Use the BYD VDS diagnostic tool to read the complete fault information, including freeze frame data (recording vehicle speed, gear position, power supply voltage, etc., at the time of the fault), and confirm the specific operating conditions when the fault occurred.
  • 2
    Check the IPB system software version against the BYD Technical Service Bulletin (TSB) to determine if a software defect exists for reverse gear signal monitoring. If necessary, upgrade the IPB control unit software or reflash the calibration.
  • 3
    Check the vehicle CAN network communication status, focusing on the Powertrain CAN physical layer: measure the resistance between CAN-H and CAN-L (standard 60Ω±5Ω) and check the wiring harness for wear, water ingress, or poor contact.
  • 4
    If the vehicle uses a hard-wired reverse gear signal: Disconnect the IPB connector and measure the reverse gear signal wire voltage (12V/B+ in reverse, 0V in neutral or P). Check circuit continuity and insulation.
  • 5
    Check the IPB control unit power supply (constant power +B, ignition switch power IG1) and ground circuit. Verify the voltage is within 9-16V and the ground resistance is less than 1Ω.
  • 6
    After clearing the fault code, perform a functional test: repeatedly shift between P/R/N/D gears, observe if "Reverse Signal Status" in the data stream changes normally, and drive in reverse to confirm if the fault reoccurs.
  • 7
    If all the above checks are normal but the fault occurs intermittently, replace the IPB integrated brake assembly (electro-hydraulic module with ECU).
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i IPB software defect causes reverse gear signal parsing error

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When shifted into Reverse, the instrument cluster intermittently displayed "Brake System Fault" and IPB set DTC C102A00. Diagnosis revealed outdated IPB software (early 2021 batch) that lost reverse gear messages under high CAN bus load (e.g., AC and headlights on simultaneously). Updating IPB control unit software to V2.5 or higher restored signal monitoring stability and cleared the fault.
BYD DTC AI Analysis

CAN bus physical layer fault interrupted reverse gear signal transmission

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While reversing, the ABS warning light suddenly came on. Retrieved DTC C102A00. Inspected the Powertrain CAN bus and found the CAN-H terminal backed out at the IPB connector, causing intermittent loss of reverse gear signal. Re-crimped the terminal and secured the connector. CAN communication returned to normal; cleared the code and it has not returned.
BYD DTC AI Analysis

Left front wheel speed sensor fault triggered IPB system warning (Reference case: C102100/C00A900)

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[Note: Reference case for similar C10 series fault codes.] ABS and ESP warning lights suddenly illuminated while driving. Scan tool showed left front wheel speed at 0. Found iron filings on the sensor head and the wiring harness broken at the steering knuckle. Replaced the left front wheel speed sensor assembly and repaired the wiring harness; fault eliminated. This demonstrates IPB system signal validity monitoring similar to C102A00 reverse gear signal logic; check the signal source, transmission line, and control unit.
Original source ↗
BYD DTC AI Analysis

Wheel Speed Sensor Intermittent Fault Diagnostic Reference (C102500/C102600)

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[Note: This is a reference case for similar fault codes in the C10 series] ABS warning light illuminated intermittently during high-speed driving. Fault code indicated intermittent left front wheel speed sensor fault. Inspection found excessive sensor installation clearance (1.8 mm, standard 0.3–1.2 mm). Loose mounting bolts caused signal fluctuation. Readjusted clearance to 0.8 mm and tightened to standard torque (10 N·m). Issue resolved. Note: For intermittent C102A00 reverse gear signal faults, also check signal source mounting stability and wiring contact reliability.
Original source ↗
BYD DTC AI Analysis

Reference Case: Simultaneous ABS, ESP, and Tire Pressure Monitoring Warnings on Song Pro

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[Note: Reference case for similar fault codes in the C10 series] After starting the vehicle, ABS, ESP and tyre pressure monitoring warning lights illuminated simultaneously and steering became heavy. Diagnosis: Water ingress and oxidation in the right front wheel speed sensor connector, plus engine bay wiring harness chafing against the body causing insulation damage and a short circuit. Repaired the damaged harness, cleaned the connector and replaced the sensor. Resolved. Note: IPB system faults (including C102A00) often trigger simultaneous multi-system warnings. Prioritize inspection of wiring harness waterproofing and insulation, especially for harnesses in the underbody and front compartment.
Original source ↗
Other Seal U Fault Codes
B1108For the BYD Song MAX (2017–2019), DTC B1108 indicates a short circuit in the PM2.5 air quality detection module (dust sensor) or its wiring harness. The sensor uses laser scattering to detect in-cabin and outside PM2.5 concentrations and transmits data to the HVAC ECU via the LIN bus or an analog signal. Short circuit conditions include: 1) Sensor power supply wire (+5V/+12V) shorted to ground 2) Signal wire shorted to power or ground 3) Short circuit in the sensor's internal photoelectric detection circuit This fault prevents the automatic climate control from switching between fresh air and recirculation based on air quality. The system enters fail-safe mode (typically forced recirculation). Severe short-circuit current can destroy the HVAC ECU sampling circuit. The system classifies this as a Level 3 severe fault and restricts vehicle operation to prevent electrical fires or controller damage. For other BYD models (such as the Qin EV, E5, and Song DM), B1108 indicates a driver-side sunload sensor fault, reflecting differences in DTC definitions across models.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.B110913DTC B110913 indicates an open signal circuit for the PM2.5 rapid detector (in-cabin air quality sensor). This sensor typically mounts inside the air conditioning system intake duct. It monitors in-cabin PM2.5 concentration in real time and provides data to the automatic air conditioning system for intelligent control of the air purification function. The BYD diagnostic protocol uses sub-code '13' to specifically indicate an open signal circuit. Although this fault theoretically affects a comfort feature, BYD Qin series vehicles classify it as a Level 3 (severe) fault. This classification occurs because the air conditioning system interacts with the battery thermal management system (e.g., monitoring battery cooling intake air quality). The fault can disable the automatic air conditioning mode and prevent the air purification function from operating. In extreme cases, it affects the battery compartment intake air quality assessment, triggering the 'repair immediately' strategy.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
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.