AU
C2A1700

DTC C2A1700 indicates the pressure compensation value in the IPB (Intelligent Power Brake) internal hydraulic circuit exceeds the normal ECU-calibrated threshold — Atto 3

Braking System

DTC C2A1700 indicates the pressure compensation value in the IPB (Intelligent Power Brake) internal hydraulic circuit exceeds the normal ECU-calibrated threshold.

Specifically, during pressure holding or build-up in the L1 hydraulic circuit (master cylinder primary circuit or a specific wheel cylinder circuit), the compensation frequency or amount the system requires to maintain target pressure constantly exceeds normal values.

Delayed pressure build-up or pressure fluctuations usually accompany this condition.

The ECU triggers this fault upon detecting abnormal hydraulic system compressibility (e.g., air ingress) or an internal leak, which forces the system to overwork to maintain pressure.

This represents a self-check anomaly within the IPB electro-hydraulic control module.

A persistent fault can cause abnormal brake pedal travel, restrict ABS/ESC functions, or disable Automatic Emergency Braking (AEB), posing a driving safety hazard.

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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1Air in the brake hydraulic system: Incomplete bleeding after replacing brake fluid or repairing brake lines, or air entering through poorly sealed line connections, increases hydraulic compressibility and forces the IPB motor to frequently compensate for pressure.
  • 2IPB electro-hydraulic module internal pressure sensor fault: L1 circuit pressure sensor signal drifts or fails, transmitting incorrect pressure values to the ECU and causing the system to falsely detect an overcompensation state.
  • 3Brake fluid contamination or deterioration: Excessive water content (>3%) or impurities in the brake fluid cause valve body binding and seal ring swelling, compromising hydraulic circuit sealing.
  • 4Damaged hydraulic valve body or sealing ring inside the IPB: Sticking L1 circuit solenoid valve or check valve, or an aged or cracked sealing ring, causes pressure leakage during the pressure-holding phase and triggers continuous compensation.
  • 5Brake line physical leak: A microscopic leak in the L1 circuit lines, hoses, or wheel cylinders causes the system to continuously detect a low-pressure condition and attempt compensation.
What To Do
  • 1
    Use a VDS2000 or Launch X431 diagnostic tool to read the complete fault codes and confirm if C2A1700 is a current fault (Active). Read the Freeze Frame data to record vehicle speed, pressure value, and pedal travel at the time of the fault.
  • 2
    Check that the brake fluid reservoir level is between MIN and MAX. Check the brake fluid colour and moisture content (using a brake fluid moisture tester). If the moisture content is >2.5% or the colour is cloudy, replace with DOT4 low-viscosity brake fluid.
  • 3
    Visually inspect the IPB module and L1 circuit lines (usually the left front wheel or master cylinder primary circuit) for obvious leaks, bulging, or loose connections. Focus on the IPB master cylinder high-pressure outlet fitting.
  • 4
    Perform the IPB system bleeding procedure (activate bleeding mode using a diagnostic tool): perform conventional bleeding in the sequence of right rear, left rear, right front, left front, then perform IPB internal bleeding. Confirm the L1 circuit is free of air.
  • 5
    After bleeding, clear the fault code and perform the IPB function test: cycle the ignition switch ON/OFF three times to complete the IPB self-check and check if the fault code returns; road test the vehicle and apply hard braking multiple times to activate the ABS, and observe if the hydraulic circuit builds pressure normally.
  • 6
    If the fault persists, use the diagnostic tool to read the real-time pressure data for the L1 circuit and compare the actual pressure with the target pressure. If the deviation is >10 bar and the motor continues to run, the IPB internal valve body or sensor is faulty. Replace the IPB electro-hydraulic module assembly with ECU.
  • 7
    After replacing the IPB module, perform coding, longitudinal acceleration sensor calibration, pedal position learning, and a signal check of the four wheel speed sensors. Finally, perform a complete road test for verification.
Real-World Cases
BYD DTC AI Analysis

C2A1700 fault code found during PDI of new BYD Song Plus DM-i

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Vehicle: 2021 Song Plus DM-i, pre-delivery PDI inspection. Symptom: No warning lights on the dashboard, but the diagnostic tool logged historical DTC C2A1700. Diagnosis: Brake fluid level checked normal; no leaks found. Tiny air bubbles detected during IPB system self-testing in transit triggered the code. Repair: Ran the IPB dedicated bleed program (activated bleed pump mode via diagnostic tool), performed three bleed cycles on the L1 circuit, cleared the DTC, and road-tested 10 km. Fault did not recur. Follow-up: Tracked for one month post-delivery. No recurrence.
BYD DTC AI Analysis

Seal 6 DM-i: Warning light on after brake caliper replacement

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Vehicle: Seal 6 DM-i, 23,000 km. Repair history: Left front collision, replaced brake hose and caliper. Fault: After replacement, ABS/ESC warning lights stayed on. DTC C2A1700 (hydraulic circuit L1 overcompensation). Diagnosis: Found left front brake line disconnected during bleeding. Suspected air entered the IPB internal L1 circuit. Conventional bleeding did not clear the fault. Resolution: Connected a diagnostic scan tool and accessed the IPB special functions. Performed "Internal Bleeding" and "Pressure Sensor Zero Calibration." Cleared the DTCs, then completed multiple emergency stops from 20 km/h to 0 km/h on a flat, straight road. System returned to normal.
BYD DTC AI Analysis

IPB sensor drift caused intermittent fault

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Vehicle: Song Pro DM-i, 48,000 km. Symptom: Intermittent "Braking System Fault" dashboard warning; DTC C2A1700 appearing sporadically, especially on cold starts. Diagnosis: Brake fluid showed no degradation; lines had no leaks; multiple bleeds ineffective. Live data revealed L1 circuit pressure sensor signal drifting 0.8 bar at rest (normal: 0±0.2 bar). Resolution: Confirmed internal IPB pressure sensor failure. Replaced IPB electro-hydraulic module assembly (with ECU), performed module coding and sensor calibration. Fault eliminated.
BYD DTC AI Analysis

Expired, contaminated brake fluid caused compensation malfunction

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Vehicle: Qin PLUS DM-i, 3 years without brake fluid change. Symptoms: ABS warning light on, brake pedal travel increased. Fault codes C2A1700 and C2A2000. Diagnosis: Brake fluid moisture content tested at 4.2%, dark brown. Disassembled IPB outlet port and found gum deposits at the valve orifice. Degraded brake fluid stuck the L1 circuit valve and degraded the seals. Solution: Replaced brake fluid, flushed lines with dedicated cleaning fluid, and cleaned the IPB valve body using a non-dismantle cleaning machine. Cleared fault codes and pedal travel returned to normal.
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.