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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 — Qin Plus

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
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Causes
Likely Causes — Qin Plus
  • 1Physical damage to the right rear wheel speed sensor wiring harness: Chassis bottoming out, driving through water, or prolonged vibration damages the harness sheath, breaks the wires, or oxidizes the internal copper strands. This commonly occurs at stress concentration points where the harness routes past the suspension control arm or through body apertures.
  • 2Connector water ingress and corrosion: Direct high-pressure washing, driving through water, or degraded seals allow water to enter the sensor connector (located near the right rear wheel hub) or the IPB module connector (in the engine compartment), causing terminal oxidation and increased contact resistance.
  • 3Internal sensor fault: Although the fault code points to the wiring harness, the IPB misinterprets an open circuit (infinite resistance) or short circuit (resistance below 0.5 kΩ) in the sensor's internal coil as a wiring fault. Normal magnetic inductive sensor resistance is 1.0-1.8 kΩ.
  • 4IPB module interface fault: Internal sampling circuit failure in the IPB assembly or poor connector contact prevents correct recognition of the right rear wheel speed signal. This condition often triggers intermittent fault codes for other wheel speed sensors.
  • 5Electromagnetic interference or shielding failure: Damaged or improperly grounded wiring harness shielding causes the high-voltage system (drive motor, DC-DC) or aftermarket electronic equipment to interfere with the wheel speed signal waveform.
What To Do
  • 1
    Initial diagnosis: Use the VDS2000/VDS3000 diagnostic tool to read all fault codes and confirm if C051200 is a historical or current code. Check the vehicle speed, wheel speed values, and IPB voltage in the freeze frame data. Verify if the right rear wheel speed displayed 0 km/h or fluctuated abnormally when the fault occurred.
  • 2
    Visual inspection: Raise the vehicle and remove the right rear wheel. Follow the sensor wiring harness route (from the wheel hub bearing → body longitudinal beam → IPB module) to check the protective sleeve for wear, breaks, or pinching. Focus on contact points between the harness and the control arm, shock absorber, and body sheet metal. Also check the sensor connector (black 2-pin) and the IPB module connector (32-pin or 48-pin, located on the left firewall in the engine compartment) for water ingress, oxidation, or terminal back-out.
  • 3
    Sensor body inspection: Disconnect the right rear wheel speed sensor connector and use a multimeter to measure the resistance between the two sensor terminals. The standard value is 1.0-1.8 kΩ (20°C). Replace the sensor if the resistance is infinite or close to 0 Ω. Measure the insulation resistance between the sensor and the vehicle body ground; it must be greater than 10 MΩ.
  • 4
    Harness continuity check: Disconnect the IPB module connector and the right rear wheel speed sensor connector. Use a multimeter in continuity mode to check circuit continuity: IPB terminal → sensor terminal (signal wire to signal wire, ground wire to ground wire). Resistance should be less than 1 Ω. Measure the circuit insulation to ground and to power; resistance should be greater than 10 MΩ. If a short circuit exists, repair the wiring harness.
  • 5
    Dynamic signal check: Refit the connector. Use an oscilloscope or diagnostic tool data stream function, rotate the right rear wheel, and observe the wheel speed signal waveform (variable reluctance type: sine wave; Hall type: square wave) and amplitude. Normal amplitude increases with wheel speed (variable reluctance type: 100-3000mV). If the signal is missing or shows excessive noise, inspect the shielding layer.
  • 6
    Repair and replacement: If the wiring harness is damaged, waterproof it using heat-shrink tubing or replace the wiring harness assembly (possible part number K2D-3639160); if the connector is oxidized, clean it with electrical contact cleaner and apply conductive grease; if the sensor is faulty, replace the right rear wheel speed sensor (remove the brake disc/drum before installation; maintain an air gap of 0.3-1.2 mm).
  • 7
    Verification test: Clear the fault code and perform a road test (maintain a vehicle speed above 40 km/h for over 5 seconds). Confirm on the diagnostic tool that all four wheel speed values are consistent and change synchronously. Verify the ABS/ESC warning light turns off, and perform an emergency braking test to confirm ABS function restoration.
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 Qin Plus 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.