AU
C102A00

DTC C102A00 indicates the IPB (Integrated Power Brake) control unit detects an invalid or abnormal reverse gear signal — Atto 3

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 — Atto 3
  • 1IPB control unit software defect or abnormal calibration data (signal parsing algorithm error)
  • 2CAN communication fault between shift actuator controller (or TCU) and IPB (wiring open circuit, short circuit, or abnormal terminating resistor)
  • 3Reverse signal hardwire connection fault (for some early models or specific configurations, including wiring open circuit or short to ground/power)
  • 4IPB internal signal sampling circuit hardware fault (input interface circuit damaged)
  • 5Vehicle 12V low-voltage power supply system fault (voltage fluctuations distort IPB signal acquisition)
What To Do
  • 1
    Use the BYD VDS diagnostic tool to read the complete fault information, including freeze frame data (recording vehicle speed, gear status, 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 identify any software defects related to reverse gear signal monitoring. If necessary, upgrade the IPB control unit software or refresh 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 inspect 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 signal wire voltage (12V/B+ in reverse, 0V in neutral/P). Check the circuit for 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: shift between P/R/N/D gears multiple times, observe if the "Reverse Signal Status" in the data stream changes normally, and drive in reverse to confirm if the fault reoccurs.
  • 7
    If all 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 Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.