AU
U040100

U040100 is a U-class network communication fault code indicating "Invalid data received from Engine Control Module (ECM)" — Qin Plus

Braking System

U040100 is a U-class network communication fault code indicating "Invalid data received from Engine Control Module (ECM)".

In the BYD DM-i hybrid architecture, the IPB (Intelligent Integrated Brake System) receives real-time parameters from the ECM via the powertrain CAN bus—including engine speed, output torque, and operating status—to coordinate the distribution ratio between regenerative and mechanical braking.

If the IPB detects an ECM data frame checksum error, data outside the physically reasonable range, a communication protocol version mismatch, or a data update timeout, it logs "ECM data corrupted" and stores this fault code.

This fault can force the IPB into a degraded mode, resulting in regenerative braking failure, restricted ESC function, and abnormal brake pedal feel.

In extreme cases, it triggers a "Brake System Fault" warning and limits vehicle power output, severely compromising driving safety.

The U040100 fault code on the Qin Plus indicates invalid data received from the Engine Control Module by the brake control system. Severity is medium because it can reduce regenerative braking, affect ESC function, and cause abnormal brake pedal feel. Common causes include poor ECM power or ground connections, or a powertrain CAN bus wiring/connector fault. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
4
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Poor contact in the ECM power supply/ground circuit: a loose fuse connection or oxidized/loose ground points G101/G102 causes unstable ECM operating voltage, leading the ECM to transmit corrupted data frames.
  • 2Powertrain CAN bus physical layer fault: short circuit or open circuit in the twisted pair between the ECM and gateway, terminal resistor drift (normally 60Ω), or oxidized connector pins (e.g., water ingress oxidizing a connector near the firewall).
  • 3ECM software fault: Interrupted flashing causing Flash data corruption, software version mismatch with VCU/IPB (e.g., ECM is V1.02 and VCU is V2.1), or lost calibration data.
  • 4Gateway controller fault: A burnt capacitor on the gateway internal PCB or a processor failure corrupts or delays ECM data packets forwarded to the IPB.
  • 5ECM hardware fault: Internal main processor (MCU) damage, CAN transceiver chip failure, or EEPROM data corruption causing continuous transmission of incorrect data frames.
What To Do
  • 1
    Safety pre-check and fault confirmation: Connect the VDS diagnostic tool to read all fault codes and freeze frame data. Record the frequency and environmental conditions of U040100 (e.g., concurrent communication faults such as U0100). Check the instrument cluster warning light status and confirm if the vehicle exhibits power limitation or braking abnormalities.
  • 2
    Basic circuit check: Check ECM fuses (EF03/EF04, etc.), relays, and connector conditions. Measure ECM supply voltage (constant B+ must be 12V±0.5V, IGN power normal). Measure resistance to ground at ground points G101/G102; resistance must be less than 1Ω. Check engine compartment wiring harness for wear or signs of water ingress.
  • 3
    CAN bus physical layer inspection: Disconnect the battery negative terminal. Measure the terminating resistance between OBD connector pin 6 (CAN-H) and pin 14 (CAN-L) (standard value: approximately 60Ω; if abnormal, check the ECM or gateway terminating resistor). Measure the CAN lines for short circuits to ground or power. Check the ECM connector pins for oxidation or blackening (focus on connectors near the firewall).
  • 4
    Communication network diagnosis: After restoring power, use VDS to perform a 'Network Test' and observe the ECM communication status. Check the powertrain CAN bus waveform (CAN-H 2.5-3.5V, CAN-L 1.5-2.5V, sleep voltage 2.5V). Use an oscilloscope to check for signal interference or waveform distortion.
  • 5
    Software version check and update: Read the current ECM, VCU, and IPB software versions. Compare them against the latest BYD TIS version bulletin to identify any version mismatches. If necessary, update the ECM software (via VDS2000 or OTA). Maintain stable voltage during the update (connect a regulated power supply). After completion, perform 'System Configuration and Calibration'.
  • 6
    Component isolation test: Disconnect the gateway and ECM connectors sequentially and measure the CAN resistance change to locate the faulty module. Perform a swap test using a known-good gateway or ECM. If the fault transfers after replacement, the corresponding module is damaged. For ECM hardware damage (e.g., accompanied by DTC P060C), perform offline programming or replace the ECM assembly, then complete immobilizer matching and parameter configuration.
Real-World Cases
BYD DTC AI Analysis

Oxidized wiring harness connector caused communication fault in Qin Pro DM

✓
Symptoms: While driving, the dashboard displayed "Check Power System", the check engine light stayed on, the vehicle automatically switched to petrol-only mode with restricted power, and EV mode was unavailable. The fault remained after turning the vehicle off and restarting. Diagnosis: VDS retrieved DTCs U040100 (Invalid Data Received from ECM) and U0100 (Lost Communication with ECM). Checked ECM power supply and ground – normal. Measured powertrain CAN bus voltage (CAN-H 2.6V, CAN-L 2.4V) – normal. Further inspection of the engine bay wiring harness found obvious oxidation and blackening on pin 15 of the ECM connector (located near the bulkhead), with contact resistance exceeding 5Ω, interrupting high-speed CAN signal transmission. Resolution: Cleaned the ECM connector pins with electrical contact cleaner, applied conductive paste, re-crimped the pins and applied waterproof sealant. Cleared the DTCs and road tested – communication restored, fault resolved.
Original source ↗
BYD DTC AI Analysis

Song Plus DM-i ECM Software Version Incompatibility

✓
Symptoms: After about 5000 km, the vehicle developed intermittent hard cold starts. Once started, engine speed fluctuated between 800–1500 rpm. The instrument panel fault light came on intermittently, especially after using cruise control. Diagnosis: Scanned DTCs and found only U040100. Checked the vehicle network topology and found data packet loss between the ECM and VCU (Vehicle Control Unit). Comparing configurations showed the ECM ran software version V1.02 while the VCU already ran V2.1. The protocol mismatch caused data frame checksum errors. Fix: Upgraded the ECM software to the latest version V2.1 (via BYD OTA or dealership VDS2000 flash). Ran the 'System Configuration and Calibration' procedure after the upgrade. The fault has not returned.
Original source ↗
BYD DTC AI Analysis

Tang DM gateway controller internal fault

✓
Symptoms: While driving, the vehicle suddenly displayed "Powertrain Severely Limited". Speed restricted to below 40 km/h; accelerator pedal unresponsive. Pulled over, shut down and restarted — fault persisted. Diagnosis: Scan tool showed DTC U040100 and communication faults U0101, U0121. Resistance between OBD pins 6 (CAN-H) and 14 (CAN-L) measured 45 Ω (normal: 60 Ω). Disconnected control modules one by one; resistance normalized only when the Gateway was unplugged. Disassembled the Gateway to find a burnt capacitor on the PCB, corrupting data packets sent to the ECM. Solution: Replaced Gateway controller (Part No.: LGX XX XXX). After replacement, performed Gateway Configuration Coding and Network Topology Learning using the scan tool. Cleared DTCs; road test normal.
Original source ↗
BYD DTC AI Analysis

Destroyer 05 ECM hardware fault (data corruption)

✓
Symptoms: After a routine software update at the dealership, the instrument cluster showed "Check Engine System." The scan tool read DTC U040100 with P060C (Internal Control Module Main Processor Performance). The vehicle could not shift into gear or drive. Diagnosis: The update logs showed communication interrupted during ECM flashing. The technician connected to the ECM with a diagnostic tool and established communication, but the data stream showed fixed values that would not change. The interrupted flash corrupted the ECM's internal Flash data. Physical layer communication remained normal, but the ECM transmitted data frames with incorrect formatting, causing the VCU to flag an "invalid data" fault. Resolution: Technicians performed offline programming on the ECM (using a dedicated programmer to rewrite the underlying data). After reinstalling the unit, they ran immobiliser matching and parameter configuration. Because some dealerships lack offline programming capability, the shop ultimately replaced the ECM assembly with a new unit to resolve the fault.
Original source ↗
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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Qin Plus →Qin Plus overview →
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.