AU
C2A1700

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

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 Qin Plus indicates abnormal pressure compensation in the IPB brake hydraulic circuit. Severity is medium because it may affect brake pedal feel and limit ABS, ESC, or AEB functions. Common causes include air in the brake system after repair or bleeding, or a faulty internal pressure sensor in the IPB module. Visit an authorised dealer for diagnosis, bleeding, and module checks. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Qin Plus
  • 1Air in the brake hydraulic system: Incomplete bleeding after replacing brake fluid or repairing brake lines, or poorly sealed line connections drawing in air, increasing hydraulic compressibility and requiring the IPB motor to frequently compensate pressure.
  • 2IPB electro-hydraulic module internal pressure sensor fault: L1 circuit pressure sensor signal drifts or fails, sending incorrect pressure values to the ECU and causing the system to falsely identify an over-compensation condition.
  • 3Brake fluid contamination or degradation: Excessive water content (>3%) or impurities in the brake fluid cause the valve body to bind and sealing rings to swell, compromising normal hydraulic circuit sealing.
  • 4Damaged IPB internal hydraulic valve body or sealing rings: Stuck L1 circuit solenoid valves or check valves, or aged or cracked sealing rings, cause pressure leakage during the pressure hold phase and trigger 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 all fault codes, confirm 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 that 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 the brake fluid with DOT4 low-viscosity brake fluid.
  • 3
    Visually inspect the IPB module and L1 circuit lines (usually the left front wheel or master cylinder first circuit) for obvious leaks, bulging, or loose fittings. Focus on the IPB master cylinder high-pressure outlet fitting.
  • 4
    Perform the IPB system bleeding procedure (use the diagnostic tool to activate bleeding mode): perform conventional bleeding in the order of right rear - left rear - right front - left front, followed by IPB internal bleeding to ensure 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 perform multiple hard braking events to activate the ABS. 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 pressure and the target pressure. If the deviation is >10bar and the motor continues running, this indicates a fault in the IPB internal valve body or sensor. 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 for all four wheel speed sensors. Finally, conduct a complete road test to verify.
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 Qin Plus 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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Qin Plus →Qin Plus 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.