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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 8

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
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

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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

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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

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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 8 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.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.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.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
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.