AU
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 3

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
5
Causes
Likely Causes — Atto 3
  • 1Loose connection or oxidation in the TCU power supply or ground circuit, causing intermittent TCU resets (inspect TCU constant power fuse F1/16, IG2 power F2/08, and ground points G201/G202).
  • 2Open or short circuit in CAN-H (orange/black) or CAN-L (orange/brown) wiring between IPB and TCU, or wiring harness chafing at the firewall grommet (common fault point on Song PLUS DM-i).
  • 3Internal TCU CAN transceiver chip damage or software crash prevents response to IPB communication requests.
  • 4Gateway module routing table error or CAN bus interference (e.g., aftermarket dash cams or audio amplifiers causing signal reflection)
  • 5IPB unit CAN communication interface circuit fault (e.g., damaged TJA1101 or TJA1043 transceiver)
What To Do
  • 1
    Use the VDS2000/VDS3000 diagnostic tool to read all network fault codes. Check for accompanying U01xx series communication faults in other modules, and access 'Network Topology' to confirm if the TCU is offline.
  • 2
    Measure the terminal resistance between OBD diagnostic connector pins 6 (CAN-H) and 14 (CAN-L) (Standard: 60±3Ω; disconnect the battery before measuring) and the static voltage (CAN-H: 2.6V, CAN-L: 2.4V).
  • 3
    Check TCU power supply: Measure TCU connector A25-1 (constant power, 12V), A25-24 (IGN, 12V), and A25-12/13 (ground, <0.1Ω). Inspect ground point G201 for oxidation.
  • 4
    Disconnect IPB connector (B25) and TCU connectors (A25/A26). Measure CAN wiring harness continuity between them (resistance <1Ω) and insulation to ground/power (>1MΩ). Closely inspect the wiring harness protective sleeve at the firewall.
  • 5
    Check the TCU software version. If earlier than version 211203, update to the latest version and perform gear position self-learning. Also verify the IPB software version matches the TCU.
  • 6
    If the wiring harness and power supply are normal, replace the TCU assembly (perform anti-theft matching, EHS motor zero-position learning, and gear position self-learning).
  • 7
    If the fault persists, replace the IPB assembly (part number HA2-3550010). After replacement, perform 'Brake System Bleeding', 'Yaw Rate Sensor Calibration', and 'Longitudinal Acceleration Sensor Calibration'.
Real-World Cases
BYD DTC AI Analysis

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

✓
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

✓
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

✓
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

✓
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

✓
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 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.