AU
U058508

DTC U058508 indicates abnormal CAN communication data between the IPB (Intelligent Integrated Braking System) and the TCU (Transmission Control Unit) — Seal U

Braking System

DTC U058508 indicates abnormal CAN communication data between the IPB (Intelligent Integrated Braking System) and the TCU (Transmission Control Unit).

Specifically, the TCU data frames received by the IPB contain checksum errors, implausible data logic, or communication timeouts.

This fault affects critical data exchange between the powertrain and braking systems.

The TCU cannot provide the IPB with accurate gear state, torque request, motor speed, or vehicle speed signals, preventing the braking system from coordinating the switching logic between energy recovery and hydraulic braking.

Potential causes include corrupted internal TCU EEPROM data, CAN bus physical layer interference, logic errors resulting from an abnormal TCU power supply, or parsing errors at the IPB receiver.

When triggered, this fault may limit vehicle power output, disable the energy recovery function, and illuminate the ABS/ESC warning light.

In severe cases, the vehicle enters Limp Home Mode.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1TCU control unit internal program crash or corrupted EEPROM data causes an abnormal transmitted CAN signal frame structure or checksum error.
  • 2Intermittent short circuit, open circuit, or excessive contact resistance in the CAN-H/CAN-L wiring harness between the TCU and IPB, especially at the firewall, in high-temperature areas of the engine compartment, or at bends in the chassis wiring harness.
  • 3Unstable voltage in the TCU power supply circuit (constant B+ or IGN power), or oxidized or loose ground points (such as G303/G304), causing abnormal TCU operating timing.
  • 4Internal fault in the IPB (Intelligent Integrated Braking System) CAN receiving module incorrectly identifies normal TCU data as abnormal data.
  • 5Non-OEM equipment (such as a dashcam or navigation module) connected in parallel to the CAN bus, or electromagnetic interference from the high-voltage system causing communication data distortion.
What To Do
  • 1
    Use the BYD VDS2000 diagnostic tool to read all DTCs. Check for accompanying communication faults, such as U059508 (MG communication fault). Confirm freeze frame data from the time of the fault, including vehicle speed and gear position.
  • 2
    Check TCU power supply fuses F1/9 (constant power) and F2/2 (IGN power). Measure the voltage at TCU connector pin 1 (B+) and pin 2 (IGN). Verify the voltage is within 11-14V with a fluctuation of less than 0.5V.
  • 3
    Measure the resistance between the TCU ground wire (pin 3) and the body ground; it should be less than 1 Ω. Check ground points G303 and G304 for corrosion or looseness.
  • 4
    Disconnect the TCU and IPB connectors. Measure the resistance between CAN-H (pin 6) and CAN-L (pin 7). Standard value: 60Ω (including terminating resistor). Inspect the wiring harness for wear or signs of water ingress.
  • 5
    Use an oscilloscope to monitor the CAN waveform at the TCU terminal. The standard dominant level is CAN-H 3.5V / CAN-L 1.5V, and the recessive level is 2.5V. Check for waveform distortion or noise interference.
  • 6
    Check the TCU and IPB connector sealing rings for aging and the pins for green corrosion. If necessary, clean with electrical contact cleaner and apply conductive grease.
  • 7
    Perform the TCU and IPB software upgrade procedure. Early software versions on some 2020-2021 BYD Song DM and Qin DM models have communication protocol compatibility issues.
  • 8
    If all above checks are normal, replace the TCU control unit assembly and complete online programming and immobilizer matching.
Real-World Cases
BYD DTC AI Analysis

Song Plus DM-i: TCU data abnormality caused braking system warning

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Vehicle: 2021 Song Plus DM-i, 32,000 km. Symptoms: While driving, the instrument cluster suddenly displayed "Check Braking System" and "Check Transmission System". The ESC and ABS warning lights illuminated and the energy recovery function failed. Diagnosis: Scanned with VDS2000 and retrieved U058508 (TCU data corrupted) and U059508 (MG communication data abnormal). TCU power supply was normal. Measuring CAN line resistance revealed 2 MΩ between CAN-H and ground on the TCU-IPB circuit (abnormally low). Further inspection found a loose wiring harness clip at the firewall. The CAN-H line insulation had chafed through against a metal bracket, causing intermittent shorts to ground after driving in rain. This caused the IPB to fail validation of TCU data frames. Solution: Repaired the damaged CAN-H wiring, insulated it with double-layer heat-shrink tubing, and re-secured the harness routing to prevent contact with the body. Cleared the fault codes and test-drove 200 km with no recurrence.
BYD DTC AI Analysis

Qin Pro DM: TCU program error causing abnormal communication data

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Vehicle: 2019 BYD Qin Pro DM, 58,000 km. Symptoms: Cold start normal. After 15–20 minutes of driving, the instrument cluster displays "Transmission function limited" and sets DTC U058508. The vehicle enters limp mode and can only drive at low speed in pure EV mode. Diagnosis: The fault only appears after TCU temperature rises. Initially suspected TCU hardware. TCU power and ground tested normal. CAN waveform normal when cold, but showed intermittent noise when hot. Found BYD technical service bulletin (TSB-2020-03): this TCU batch has a software bug. Under high temperatures, EEPROM data reads incorrectly, causing transmitted gear signals to exceed valid ranges; the IPB flags this as data corruption. Solution: Upgraded TCU software to V2.3.5. After upgrading, conducted a continuous one-hour road test. No fault occurred even when TCU temperature exceeded 75°C. Fault resolved.
BYD DTC AI Analysis

Water ingress in Song DM TCU connector caused data communication error

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Vehicle: 2020 Song DM, 41,000 km, accident-damaged and repaired. Symptoms: After front-end repairs, multiple warning lights flashed on the instrument cluster at startup. Scan tool retrieved U058508 and multiple communication faults. Diagnosis: Found front compartment wiring harness damage from the accident. The TCU connector (located at the left front fender liner) had a broken seal cap latch. Recent rain exposure allowed water into the connector; pins 6 (CAN-H) and 7 (CAN-L) showed electrochemical corrosion, causing CAN signal impedance mismatch. The IPB could not correctly parse data frames from the TCU. Repair: Replaced the TCU connector assembly (includes wiring harness Repair Kit), wrapped it with specialized waterproof tape, replaced the damaged seal ring, cleaned the TCU socket with WD-40 Precision Electrical Cleaner, and cleared fault codes. Communication returned to normal.
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.