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C051200

DTC C051200 indicates the IPB (Intelligent Integrated Braking System) detected a persistent or intermittent electrical fault in the right rear wheel speed sensor (RR WSS) circuit — Atto 3

Braking System

DTC C051200 indicates the IPB (Intelligent Integrated Braking System) detected a persistent or intermittent electrical fault in the right rear wheel speed sensor (RR WSS) circuit.

This fault occurs when the IPB module fails to receive a valid wheel speed signal within the specified time, or detects signal voltage/resistance outside the threshold range (typically an open circuit, short to ground, short to power, or signal interference).

On vehicles equipped with the IPB (One-box) integrated braking system, such as the BYD Song PLUS DM-i, this fault disables or limits the Anti-lock Braking System (ABS), Electronic Stability Control (ESC), Automatic Emergency Braking (AEB), Hill Hold Control (HHC), and Adaptive Cruise Control (ACC) functions.

Additionally, because New Energy Vehicles (NEVs) rely on wheel speed signals to calculate regenerative braking torque, this fault may cause abnormal energy recovery, inaccurate driving range display, and force the drive system into protection mode.

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Cases Logged
Real-World Cases
BYD DTC AI Analysis

Intermittent right rear wheel speed failure on Song PLUS DM-i after water wading

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Model: Song PLUS DM-i 2021, 23,000 km. Symptoms: ABS and ESC warning lights on the instrument cluster lit intermittently after driving through water in wet weather. Scanner showed current code C051200. Diagnosis: Found the right rear wheel speed sensor connector (located on the inner side of the rear suspension trailing arm) had water inside with green oxidation on the pins. Harness continuity tested good; sensor resistance measured 1.2kΩ (normal). Cause: Connector seal deteriorated, allowing moisture entry during water crossings and causing intermittent poor contact. Repair: Cleaned connector pins with anhydrous ethanol, applied electrical contact protectant after drying, and replaced the waterproof seal. Resolved. Advised owner to avoid directing high-pressure water at the inner wheel hubs.
BYD DTC AI Analysis

Wiring harness chafing caused an open circuit in the right rear wheel speed signal

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Model: BYD Song Pro DM, 58,000 km. Issue: ESC warning light came on steadily while driving. Active DTC C051200; live data showed right rear wheel speed stuck at 0. Troubleshooting: Visual inspection found the right rear wheel speed wiring harness sheath worn through at the rear subframe clip. Three of the four internal copper wires were broken; only one remained connected. Cause: Long-term driving on unsealed roads caused the harness to rub against the metal bracket, resulting in fatigue fracture. Fix: Cut out the worn harness section and spliced in matching wire (0.5mm² shielded twisted pair) using soldered joints. Applied triple-layer heat shrink tubing for insulation and waterproofing. Rerouted and secured the harness to avoid contact with sharp objects. Cleared the codes and confirmed normal operation.
BYD DTC AI Analysis

False fault from loose IPB connector

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Model: Han EV, mileage 11,000 km. Symptoms: C051200 DTC appeared intermittently after 3,000 km from new, accompanied by "Automatic Emergency Braking Limited" warning. Tapping below the instrument panel cleared the fault. Diagnosis: Measured right rear wheel speed sensor and harness resistance—both normal. Inspected the IPB module (left side of engine bay) 32-pin connector and found pin 15 (RR WSS signal) backed out, lock tab not fully engaged. Cause: Assembly did not fully lock the connector; vehicle vibration gradually worked the pin loose. Repair: Reinserted the pin and confirmed the lock tab engaged. Applied silicone-based grease to prevent oxidation. Secured the IPB wiring harness with cable ties. Monitored for one month with no recurrence.
BYD DTC AI Analysis

Sensor internal open circuit misdiagnosed as wiring fault

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Model: Tang DM-i, 42,000 km. Symptom: Instrument cluster displayed brake system fault; retrieved DTC C051200. Troubleshooting: Measured infinite resistance at the sensor connector, initially suspected an open circuit in the wiring. However, continuity from the IPB end checked normal. Disassembling the sensor revealed internal coil leads fractured from prolonged high temperatures (proximity to brake disc). Root cause: Internal sensor failure; the DTC indicates a wiring fault because the IPB detected an open circuit. Solution: Replaced the right rear wheel speed sensor (P/N SC-3630100), adjusted the sensor-to-tone ring air gap to 0.8mm during installation. Cleared the DTCs and road tested — signal normal at all vehicle speeds.
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: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.