AU
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 — Seal U

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
5
Causes
Likely Causes — Seal U
  • 1Internal carbon track wear or contact oxidation in the brake pedal position sensor (primary/secondary) causes signal interruption.
  • 2Mechanical binding, spring fatigue, or seal failure of the internal button switch mechanism in the IPB electro-hydraulic module.
  • 3Water ingress and corrosion in the wiring harness connector (especially at the pass-through between the engine compartment and cabin) causing the signal wire to short to ground.
  • 4IPB control unit software version bug causes switch signal validation error.
  • 5Moisture ingress after vehicle wading or washing causes a short circuit on the IPB assembly internal circuit board.
What To Do
  • 1
    Use the VDS diagnostic tool to read the DTC freeze frame data and record the pedal travel value, vehicle speed, and system voltage when the fault occurred.
  • 2
    Check the physical connection of the brake pedal position sensor (located above the pedal bracket). Measure the voltage at sensor pin 1 (+5V reference voltage) and pin 2 (signal output) to verify the voltage changes linearly with pedal travel (normal range: 0.5–4.5V).
  • 3
    Check the IPB electro-hydraulic module power supply (30A constant power), the resistance at ground points G101/G102 (< 1Ω), and the CAN line waveforms (CAN-H 2.6-2.8V, CAN-L 2.2-2.4V).
  • 4
    Perform the IPB system bleeding procedure (requires the dedicated brake fluid extraction tool) and calibrate the pedal position sensor zero point (access the IPB special function menu via VDS).
  • 5
    If circuit measurements are normal but the fault remains, replace the IPB integrated electro-hydraulic brake module assembly, complete the new module coding configuration, and calibrate the longitudinal acceleration sensor.
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 Seal U Fault Codes
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.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.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.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.