AU
C052901

DTC C052901 indicates a communication interruption or loss of data validity between the IPB (Intelligent Integrated Braking System) control unit and the Steering Angle Sensor (SAS) — Seal U

Braking System

DTC C052901 indicates a communication interruption or loss of data validity between the IPB (Intelligent Integrated Braking System) control unit and the Steering Angle Sensor (SAS).

The steering angle sensor mounts on the steering column and transmits steering wheel angle, rotational speed, and direction information in real time to the IPB, VCU, ADAS, and other modules via the CAN bus.

It provides the core input signal for the Electronic Stability Control (ESC), automatic parking, lane keeping, and Autonomous Emergency Braking (AEB) systems.

The IPB triggers this fault when it fails to receive a valid steering angle data frame within 500 ms, or detects a sensor response timeout or checksum error.

The vehicle then enters a degraded mode: ESC function is limited or disabled, skid control fails, and automatic parking is unavailable.

Extreme cases may alter brake assist characteristics, but the system retains basic hydraulic braking.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Internal steering angle sensor fault: Damaged Hall effect element, internal MCU crash, or EEPROM data loss preventing valid signal output.
  • 2Steering column wiring harness connection fault: Steering angle sensor connector beneath the steering wheel (usually integrated into the combination switch assembly) is loose, has backed-out pins, or shows water ingress and oxidation, or the wiring harness is worn or broken from frequent steering column rotation.
  • 3Power supply and ground fault: 12V battery voltage below 10V, blown sensor power supply fuse, or poor ground circuit contact causing sensor initialization failure.
  • 4IPB system software defect: Early software versions have low fault tolerance for steering angle sensor signals and incorrectly flag the module as lost during rapid steering inputs or voltage fluctuations.
  • 5Modification or external interference: Installing a non-genuine steering wheel, installing an OBD window closer or steering wheel trim that causes physical interference, or an external device occupying the CAN bus and causing communication congestion.
What To Do
  • 1
    Diagnostic scan: Use VDS2000/VDS3000 to access the IPB system. Read the complete fault codes and freeze frame data. Check for accompanying related faults such as C052B (steering angle sensor signal error) and U0416 (IPB communication fault). View the live data stream to confirm if the steering angle value displays as 'invalid' or remains at a fixed value that does not change when turning the steering wheel.
  • 2
    Basic check: Disconnect the 12V battery negative terminal for 5 minutes. Reconnect power and observe if the fault code changes to a history code. Inspect the combination switch connector (grey or black 18-pin connector) on the steering column below the steering wheel for looseness, backed-out pins, or water corrosion. Clean and apply conductive grease if necessary.
  • 3
    Circuit measurement: Keep the ignition switch in the ON position and measure the values at the steering angle sensor connector: power supply (Pins 1/2) should be 12V ± 0.5V, ground (Pins 3/4) less than 0.1Ω, CAN-H (Pin 5) approximately 2.6-2.8V, and CAN-L (Pin 6) approximately 2.2-2.4V. Disconnect the battery and measure the CAN terminal resistance; it should be approximately 60Ω.
  • 4
    Sensor calibration: Select 'Special Functions' → 'Steering Angle Sensor Calibration' on the diagnostic tool. Follow the prompts to center the steering wheel (within ±5°) and perform zero-position learning. Turn the steering wheel fully left and hold for 2 seconds, turn fully right and hold for 2 seconds, then return to center. After a successful calibration, read the data stream to confirm the angle value is 0°±3°.
  • 5
    Software update: Check the IPB control unit software version against the BYD technical bulletin (e.g., TPI-2022-BYD-035). If the version is below V2.1.8, update to the latest version to optimize steering angle sensor signal processing logic.
  • 6
    Component replacement: If the above steps fail, replace the steering column combination switch assembly (part number SA-3774100 or corresponding model number). After replacement, recalibrate the steering angle and initialize the ESC system. Finally, perform a road test at speeds above 20 km/h to verify ESC function.
Real-World Cases
BYD DTC AI Analysis

Song PLUS DMi steering wheel modification caused connector to come loose

✓
A 2021 Song PLUS DMi developed DTC C052901 and the ESC warning light came on after the owner fitted a carbon fibre steering wheel. Inspection revealed the owner had never disconnected the steering column connectors during the modification; forced pulling backed out pin 3 (CAN-H) of the 8-pin steering angle sensor connector. The technician re-crimped the terminal, applied conductive grease, performed steering angle calibration and cleared the fault. When modifying the steering wheel, disconnect all steering column connectors and avoid rough handling.
BYD DTC AI Analysis

Outdated IPB software triggered false alarms.

✓
After jump-starting due to a flat battery, DTC C052901 appeared frequently, especially during cold starts. Testing showed normal power and communication at the steering angle sensor, but the data stream revealed a 10-15ms signal interruption during startup. A technical bulletin check confirmed this VIN is part of a software defect batch (IPB V2.1.2). Upgrading to V2.2.5 enhanced fault tolerance for steering angle sensor communication jitter at startup, and the fault has not recurred.
BYD DTC AI Analysis

Water ingress caused internal corrosion of combination switch

✓
After water ingress above wheel center, the vehicle set C052901 and the ABS light came on. Disassembling the steering column revealed the steering angle sensor seal had degraded. Water entered through the steering shaft, corroding and shorting the PCB. Replaced the combination switch assembly, dried the wiring harness connectors, and repaired the body sealing to resolve the fault. Advise checking the steering column base drainage immediately on any vehicle that has been through water.
BYD DTC AI Analysis

Prolonged dry steering caused wiring harness chafing

✓
The ride-share vehicle had travelled 120,000 km. Frequent dry steering fractured the steering column wiring harness retaining clip. Steering movements pulled the harness, causing the internal copper conductors of the CAN-L line to break while the insulation remained intact. Resistance measurements showed intermittent infinite resistance in the CAN line. Replaced the wiring harness, re-secured the routing, and added protective sleeving to complete the repair.
BYD DTC AI Analysis

Steering angle sensor zero position offset not calibrated

✓
Replaced the front subframe and steering gear after accident repairs without calibrating the steering angle sensor. While driving, fault codes C052901 and C052B triggered randomly. Live data showed -15° steering angle with the steering wheel straight. Performed 'Steering Angle Sensor Calibration' and 'ESC System Longitudinal Acceleration Sensor Calibration'. Live data then read 0°, codes cleared, and road test passed.
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.