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C104C04

DTC C104C04 indicates a signal failure in the brake pedal position detection switch or internal mode switch within the Integrated Power Brake (IPB) system — Qin Plus

Braking System

DTC C104C04 indicates a signal failure in the brake pedal position detection switch or internal mode switch within the Integrated Power Brake (IPB) system.

In the BYD brake-by-wire architecture, the IPB monitors this switch signal to identify driver braking intent and trigger hydraulic pressure build-up.

Switch failure prevents the IPB from accurately identifying pedal travel status, forcing the system into Limp Home mode with limited brake assist.

This condition may cause a stiff brake pedal, increased braking distance, and disabled ESC/ABS functions, constituting a severe fault that compromises driving safety.

3
Cases Logged
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i IPB switch failed after wading through water

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After driving through a flooded section of road, the dashboard displayed "Brake System Fault" and the ABS/ESC warning lights illuminated. Retrieved DTCs C104C04 (switch failure) and C104008 (signal plausibility fault). Inspection found the IPB mounted on the left side of the front compartment. Water surge during the wading caused the bottom seal of the module to leak. Disassembled the IPB and found the pedal travel detection switch contacts on the internal PCB corroded and oxidized. Replaced the IPB assembly and waterproofed the wiring harness connectors to resolve the fault.
BYD DTC AI Analysis

Worn brake pedal sensor wiring harness caused intermittent fault

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The brake system warning light occasionally illuminates when driving on rough roads, but not on flat surfaces. DTC C104C04 is present as an intermittent current fault. Inspection found the brake pedal position sensor harness chafing against the steering column mounting bracket during repeated pedal movement; the chafing wore through the signal wire insulation and caused a short to earth. Repaired the harness, rerouted and secured it to maintain more than 15mm clearance from moving parts. Fault has not reoccurred.
BYD DTC AI Analysis

Internal mechanical sticking in the IPB caused abnormal switch signals

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While driving normally, the brake pedal suddenly went hard and the instrument cluster displayed a brake system fault. Retrieved DTC C104C04 with the scan tool, but the code would not clear. The pedal position sensor output voltage measured normal, yet the switch status fed back from the IPB did not match the sensor's actual position. Determined the cause to be sticking of the master cylinder pushrod switch mechanism inside the IPB. Replaced the IPB assembly, bled the brake system and calibrated the ESC sensors. Brake assist 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.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.