AU
C120700

DTC C120700 indicates the hydraulic pump motor inside the IPB (Integrated Power Brake) fails to return to its initial mechanical position (Home Position) within the specified time (typically 200-500 ms) after completing brake boost pressure build-up or an ABS/ESC control action — Atto 3

Braking System

DTC C120700 indicates the hydraulic pump motor inside the IPB (Integrated Power Brake) fails to return to its initial mechanical position (Home Position) within the specified time (typically 200-500 ms) after completing brake boost pressure build-up or an ABS/ESC control action.

This fault stems from a malfunction in the motor mechanical return mechanism, Hall position sensor signal feedback, or ECU closed-loop control logic.

Upon setting this DTC, the IPB enters Limp Home Mode, resulting in a stiff brake pedal and reduced brake assist.

The system disables ABS/ESC active intervention and retains only basic hydraulic braking, severely compromising driving safety.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Excessive carbon brush wear or a burned commutator in the internal DC motor of the IPB electro-hydraulic module causes the motor to seize in one position and fail to rotate.
  • 2Motor position sensor (usually a dual Hall sensor) signal drift, damage, or connector water ingress and oxidation, preventing the ECU from identifying the actual position.
  • 3Mechanical binding inside the IPB hydraulic unit, such as piston seal ring aging and swelling or brake fluid impurity particles causing jamming, resulting in excessive motor load.
  • 4IPB ECU internal motor drive circuit fault, such as a shorted H-bridge MOSFET or damaged gate driver chip, resulting in an abnormal return control signal.
  • 5Power supply system fault, such as low battery voltage (<10.5V) or high ground resistance, causing insufficient motor torque to overcome mechanical resistance and return to position.
What To Do
  • 1
    Use the VDS2000/3000 diagnostic tool to read the complete fault codes and freeze frame data. Confirm C120700 is a Current DTC and record parameters such as vehicle speed and pedal travel at the time of the fault.
  • 2
    Visually inspect the IPB assembly to confirm no brake fluid leakage or signs of impact deformation. Check harness connectors C1 and C2 for backed-out pins, oxidation, or water ingress, and measure the retaining clip holding force.
  • 3
    Measure the IPB supply voltage: Use a multimeter to measure the voltage at the +B (constant power) and IG1 (ignition switch power) terminals. The standard value is 12V±0.5V, and the voltage drop during a load test must be <0.3V.
  • 4
    Perform the IPB hydraulic bleeding procedure: Use the diagnostic tool to enter the 'Brake System Bleeding' function. Execute the procedure in the following sequence: right rear - left rear - right front - left front. Check the pump motor for smooth operation and abnormal noise.
  • 5
    Actuator active test: Enter 'IPB Function Test' and activate the pump motor. Use a stethoscope to verify the motor running sound is even. Monitor the motor current waveform (normal: smooth square wave; abnormal: sawtooth or flat-top wave).
  • 6
    If diagnostics confirm an internal fault, replace the IPB with ECU assembly (part number varies by model, e.g., Song PLUS DM-i: 6A-3505010X). When removing the old part, note the brake line markings to prevent cross-contamination.
  • 7
    Perform a complete calibration after replacement: a) Write IPB coding using the diagnostic tool; b) Calibrate the longitudinal acceleration sensor and yaw rate sensor; c) Re-bleed the brake system; d) Perform a road test to verify ABS/ESC functions.
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i IPB Pump Motor Mechanical Jam Case

✓
On arrival, the instrument cluster showed ABS, ESC, and automatic emergency braking warning lights, with the brake pedal noticeably stiff. Retrieved DTC C120700 (current code). Freeze frame data showed the fault occurred at 15 km/h. Removed and inspected the IPB assembly, finding severe burning on the internal DC motor commutator and carbon brush dust accumulation that caused rotor seizure. Measured motor resistance at 8.5Ω (normal 3-5Ω), confirming internal short circuit. Replaced the IPB assembly with ECU, performed coding and bleeding procedures, and cleared the fault.
BYD DTC AI Analysis

Position Sensor Signal Fault After Water Ingress

✓
The owner reported the dashboard occasionally displayed a 'Brake System Fault' warning after driving in wet conditions, clearing after an ignition cycle. Diagnosis revealed historic DTC C120700. Inspection found traces of water and white oxidation inside IPB connector C1. Analysis indicated water had entered through the wiring harness grommet during water wading, causing a momentary short in the Hall sensor signal. Cleaned the connector contacts with electronic cleaner, applied conductive grease, re-wrapped the joint with waterproof tape, and fitted an additional waterproof boot. No faults returned during one month of follow-up.
BYD DTC AI Analysis

False Alarm Case Due to Battery Discharge

✓
After extended parking, C120700 set with a "Check Battery" warning. Battery voltage measured only 10.2V; State of Health (SOH) was below 40%. The IPB ECU logged a motor return timeout during startup voltage sag; insufficient voltage caused the motor to rotate too slowly. Replaced the battery, fully charged it, cleared the code, and performed an IPB power reset (disconnected negative terminal for 10 minutes). Fault has not returned.
BYD DTC AI Analysis

Case: Brake Fluid Contamination Causing Hydraulic Sticking

✓
The workshop reported multiple Song PLUS DM-i vehicles from the same production batch simultaneously developed C120700 faults. Inspection found severely contaminated brake fluid with moisture content >4% (standard <1%) and metal debris. Substandard brake fluid used at an unauthorized shop corroded the IPB internal valves and seized the pistons; excessive motor load prevented the motor from returning. Replaced the IPB assembly, thoroughly flushed all brake lines, and filled with Bosch DOT4 brake fluid. Fault resolved.
BYD DTC AI Analysis

Software update resolved false alarm

✓
No abnormal braking feel, but scan tool showed C120700 intermittently. Found IPB software at V1.02. TSB confirms this version has a bug: return time threshold too strict. Upgraded IPB ECU software to V1.05. Fault code cleared automatically after upgrade. Drove 100 km continuously with no recurrence. Confirmed software false positive.
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.