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C1101

DTC C1101 indicates the ABS (Anti-lock Braking System) ECU detected its 12V low-voltage supply exceeds the system safety threshold (typically >16V-18V, depending on vehicle calibration) — Atto 3

Braking System

DTC C1101 indicates the ABS (Anti-lock Braking System) ECU detected its 12V low-voltage supply exceeds the system safety threshold (typically >16V-18V, depending on vehicle calibration).

In BYD new energy vehicles, the DC-DC converter converts high-voltage traction battery power to supply 12V to the ABS.

When the ECU detects an abnormally high supply voltage, it triggers the overvoltage protection mechanism.

This may cause ABS, ESP, EBD, HHC (Hill Hold Control), and Automatic Emergency Braking functions to fail or enter a degraded mode.

Unlike a high-voltage insulation fault, this indicates a power management abnormality in the 12V low-voltage system, which directly affects braking safety performance.

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Cases Logged
Real-World Cases
BYD DTC AI Analysis

BYD E2 DC-DC converter fault causing ABS overvoltage warning

✓
A 2020 BYD E2 with 30,000 km had the ABS, ESP and EBD warning lights illuminate simultaneously. The scan tool showed DTC C1101 System High Voltage. Measuring the 12V battery revealed 16.2V in READY mode, fluctuating with accelerator pedal position. The DC-DC converter output was unstable. Replaced the DC-DC module inside the high voltage distribution box; voltage returned to 14.1V. Cleared the fault codes; fault resolved.
BYD DTC AI Analysis

BYD Yuan EV auxiliary battery ageing caused C1101 fault

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2019 Yuan EV. Brake system warning light illuminated intermittently in winter. Diagnostic scanner retrieved historical fault code C1101. Testing revealed the 12V battery static voltage was 12.1V (low), spiking to 15.8V momentarily during charging. Replaced the 12V battery; charging voltage stabilised at 14.2V and the fault has not recurred. Plate sulfation increased internal resistance and reduced charge acceptance, causing momentary system overvoltage that triggered protection.
BYD DTC AI Analysis

ABS hydraulic modulator internal circuit fault — false positive

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BYD E1 accident repair. C1101 fault code appeared after replacing the front compartment wiring harness. Measured power supply voltage at 13.8V (normal). Found water ingress and oxidized pins at the ABS pump connector. Cleaned the pins but the fault persisted. Disassembled the ABS unit and found the power management chip on the ECU board damaged. Replaced the ABS hydraulic modulator assembly with integrated ECU; fault cleared. Suspect internal circuit damage from reverse polarity connection during the accident or repair.
BYD DTC AI Analysis

Loose ground point caused abnormal voltage detection

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The BYD E3 ABS warning light occasionally lit up on rough roads; the scanner read C1101. Inspection found the battery negative ground cable loose at the front compartment ground point G106, with oxidation. After tightening and cleaning the ground point, resistance in the ABS module ground circuit dropped from 3.2Ω to 0.3Ω. A 20 km road test showed no fault recurrence. A high-resistance connection caused ECU reference ground potential drift, leading to incorrect supply voltage calculations.
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: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.