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 8

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.

The C2A1700 fault code on the Atto 8 indicates abnormal pressure compensation in the IPB brake hydraulic circuit, usually during pressure hold or build-up. Severity is medium, as it may affect brake pedal feel and limit ABS, ESC, or AEB functions. Common causes include air in the brake lines after poor bleeding or an internal IPB pressure sensor fault. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Atto 8
  • 1Air in the brake hydraulic system: Incomplete bleeding after replacing brake fluid or repairing brake lines, or poor sealing at line connections drawing in air. This increases hydraulic compressibility and causes the IPB motor to frequently compensate for pressure.
  • 2IPB electro-hydraulic module internal pressure sensor fault: L1 circuit pressure sensor signal drift or failure sends incorrect pressure values to the ECU, 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 swelling, compromising normal hydraulic circuit sealing.
  • 4Damaged hydraulic valve body or sealing ring inside the IPB: A sticking solenoid valve or check valve in the L1 circuit, or an aged and cracked sealing ring, causes pressure leakage during the pressure-holding phase and triggers continuous compensation.
  • 5Brake line physical leak: 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 the VDS2000/Launch X431 diagnostic tool to read the complete fault codes, verify if C2A1700 is a current fault (Active), and read the Freeze Frame data to record vehicle speed, pressure value, and pedal travel when the fault occurred.
  • 2
    Check if the brake fluid reservoir level is between MIN and MAX. Check the brake fluid color and moisture content using a brake fluid moisture tester. If the moisture content is >2.5% or the color is cloudy, replace with DOT4 low-viscosity brake fluid.
  • 3
    Visually inspect the IPB module and L1 circuit lines (typically the left front wheel or primary master cylinder 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 the diagnostic tool): perform conventional bleeding in the sequence of right rear, left rear, right front, and left front, then perform IPB internal bleeding to ensure the L1 circuit is free of air.
  • 5
    After bleeding the system, 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; perform a road test with multiple hard braking applications to activate the ABS and observe if the hydraulic circuit pressure builds normally.
  • 6
    If the fault persists, use the diagnostic tool to read the L1 circuit real-time pressure data and check the deviation between the actual and target pressures. If the deviation is >10bar 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 the following: coding, longitudinal acceleration sensor calibration, pedal position learning, and a signal check for all 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 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.