AU
C058800

DTC C058800 indicates the signal voltage of the brake booster Motor Position Sensor (MPS) inside the Integrated Power Brake (IPB) electro-hydraulic module falls below the ECU threshold (typically below 0 — Seal U

Braking System

DTC C058800 indicates the signal voltage of the brake booster Motor Position Sensor (MPS) inside the Integrated Power Brake (IPB) electro-hydraulic module falls below the ECU threshold (typically below 0.5V or 10% of the reference voltage).

The sensor uses electromagnetic or Hall effect principles to monitor the booster motor rotor position in real time, enabling closed-loop control of the motor torque output and brake assist level.

When the ECU detects the sensor voltage remains continuously below the calibrated value, it sets a circuit undervoltage fault.

This fault prevents the IPB system from accurately determining the motor position, which limits or disables the electric brake assist function.

As a result, the vehicle may enter Limp Home Mode, the brake pedal becomes hard, and the ESC/ABS warning lights illuminate.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Internal short circuit in the motor position sensor or component aging: a short circuit in the sensor's internal coil or damage to the Hall element pulls the output voltage low.
  • 2Wiring harness short to ground or connector fault: damaged sensor wiring harness insulation causing a short to the vehicle body, or water ingress, oxidation, or loose connector pins causing excessive contact resistance.
  • 3Abnormal IPB module internal power supply circuit: Internal 5V reference voltage regulator fault or filter capacitor short circuit causes insufficient sensor supply voltage.
  • 4Sensor signal wire chafing: The wiring harness rubs against a metal edge of the vehicle body. Long-term vibration wears through the wire insulation, causing a short to ground.
  • 5Extreme low temperatures or electromagnetic interference: Although rare, sensor characteristic drift in extreme environments or strong electromagnetic interference can trigger a momentary false undervoltage reading.
What To Do
  • 1
    Fault confirmation and freeze frame analysis: Use VDS or X-431 to read DTC C058800 and freeze frame data. Record parameters such as vehicle speed, voltage, and temperature when the fault occurred. Confirm whether the fault is Current or History.
  • 2
    Visual and connector inspection: Check the IPB module exterior for impact damage or leakage. Disconnect the IPB wiring harness connector. Check the pins for corrosion, backed-out terminals, or signs of water ingress. Test the connector sealing.
  • 3
    Sensor supply voltage measurement: With the key ON, measure the voltage to ground at the motor position sensor supply pin on the IPB connector (typically the 5V reference voltage). Standard value: 4.8-5.2V. If the voltage is below 4.5V, check the module internal power supply circuit.
  • 4
    Signal line voltage and continuity check: Measure the voltage at the sensor signal feedback pin. Normal voltage varies continuously between 0.5-4.5V. If the voltage is 0V, measure the wiring harness continuity from the IPB to the sensor (internal) and the insulation resistance to ground. The insulation resistance must be greater than 10MΩ.
  • 5
    Dynamic signal monitoring and load testing: Use an oscilloscope to monitor the sensor signal waveform while operating the brake pedal. Check for signal interruptions or voltage drops. Perform a road test and observe if the fault recurs under specific conditions (such as hard braking or driving over bumps) to rule out intermittent poor contact.
  • 6
    IPB assembly replacement and calibration: If diagnostics confirm an internal sensor fault or internal module circuit fault (the sensor is typically integrated with the IPB and not serviced separately), replace the IPB electro-hydraulic module assembly. After replacement, perform the bleeding procedure, sensor zero-point calibration, and ESC function test.
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i brake booster failure after wading

✓
After driving through flood water, the instrument cluster displayed "Braking System Fault". Scanning showed DTC C058800. Found the IPB module in the left front wheel arch. The connector waterproof seal had deteriorated, letting water in to oxidise the pins and create a 0.8kΩ short between the sensor supply pin and ground. Cleaned and dried the connector, applied conductive grease, and temporarily cleared the fault, but it returned after one week. Replaced the IPB wiring harness connector and sealed it properly to permanently fix the issue.
BYD DTC AI Analysis

Wiring harness wear causes intermittent low voltage

✓
When driving on rough roads, the brake pedal intermittently hardened and DTC C058800 appeared. Static voltage measurements normal. Found the IPB-to-body harness loose at the firewall penetration; vibration wore through the insulation, exposing copper wires that shorted to ground. Rewrapped the harness, adjusted the clip positions, and ensured 10 mm or more clearance from the body. The fault has not reoccurred.
BYD DTC AI Analysis

Replaced IPB module assembly due to internal sensor failure.

✓
Vehicle started with ABS warning light on; DTC C058800 present. External harness power supply measured 5.02V (normal). Signal wire showed continuity to ground (abnormal). Disconnected external harness and measured IPB internal sensor pins directly: still showed short to ground (<1Ω). Determined IPB internal motor position sensor coil short. Replaced IPB electro-hydraulic module assembly, bled brake system, performed ESC calibration and cleared DTC. Assist function restored.
Other Seal U 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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.