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U058504

U058504 indicates a private CAN or powertrain CAN communication timeout fault between the IPB (Intelligent Integrated Braking System) and the TCU (Transmission Control Unit) — Atto 8

Braking System

U058504 indicates a private CAN or powertrain CAN communication timeout fault between the IPB (Intelligent Integrated Braking System) and the TCU (Transmission Control Unit).

In the BYD DM-i architecture, the IPB requires real-time key data from the TCU, including motor torque, vehicle speed, gear position, and regenerative braking requests, to coordinate brake force distribution and regenerative braking.

The IPB triggers this fault if it fails to receive a valid data frame from the TCU within a 500ms monitoring period (normal message cycle is 10-20ms), or if it receives data checksum errors for more than 10 consecutive frames.

This fault disables the regenerative braking function and forces the ESC/ABS into degraded mode.

In extreme cases, it triggers the powertrain Limp Home mode, limiting vehicle speed.

5
Cases Logged
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i G202 ground point oxidation causing intermittent communication loss

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A 2021 Song PLUS DM-i with 20,000 km intermittently displayed 'Braking System Fault' on the instrument cluster. Scan showed DTC U058504 (history). When the fault occurred, regenerative braking failed. Inspection found the TCU ground point G202 (located on the left front side member) had a loose bolt with oxidised contact surfaces, causing the TCU operating voltage to fluctuate between 11.2-12.8V and interrupting CAN communication. Cleaned the ground point, applied conductive grease, and tightened the bolt to the standard torque of 25 N·m. Fault resolved.
BYD DTC AI Analysis

Backed-out pin in IPB connector B25 caused CAN-H open circuit

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During new vehicle PDI, found current fault code U058504 that would not clear. Inspected IPB wiring harness connector B25 and found pin 18 (CAN-H) backed out approximately 2mm, interrupting communication with the TCU. Cause: improper assembly during production. Repair: Replaced the backed-out female terminal, reconnected the connector, and applied waterproof sealant. Cleared the fault code; road test normal.
BYD DTC AI Analysis

Firewall wiring harness damaged after accident repair

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After front-end collision repairs, the vehicle frequently set U058504. Inspection found the accident had ruptured the wiring harness protective sleeve at the firewall; the IPB-to-TCU CAN-H line was chafing against the body sheet metal and intermittently shorting to ground (insulation resistance: 200Ω). Replaced the damaged 20 cm harness section, re-wrapped and secured the routing, and added rubber protective sleeves. Fault resolved.
BYD DTC AI Analysis

Aftermarket DSP amplifier caused CAN bus interference

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After the owner fitted an aftermarket audio system (high-power DSP amplifier), U058504 and multiple system warning lights lit up intermittently while driving. Inspection found the amplifier power cable ran parallel to the CAN harness, causing electromagnetic interference (oscilloscope showed glitches on the CAN waveform). Rerouted the amplifier power cable to maintain >20cm clearance from the CAN harness and installed ferrite cores on the CAN lines at the TCU and IPB. Fault frequency dropped significantly; issue resolved.
BYD DTC AI Analysis

IPB and TCU software version mismatch

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After the TCU software upgrade at the dealership (optimising EHS shift logic), the vehicle developed a U058504 fault that would not clear. Inspection found the IPB software remained at the old version (V1.02), incompatible with the new TCU (V2.15) communication protocol, causing a data length validation failure. Upgraded IPB software to V1.08 and performed 'brake system calibration' and 'longitudinal acceleration sensor learning'. Fault cleared.
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.