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U040100

U040100 is a U-class network communication fault code indicating "Invalid data received from Engine Control Module (ECM)" — Atto 8

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.

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Cases Logged
Real-World Cases
BYD DTC AI Analysis

Oxidized wiring harness connector caused communication fault in Qin Pro DM

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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.
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BYD DTC AI Analysis

Song Plus DM-i ECM Software Version Incompatibility

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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.
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BYD DTC AI Analysis

Tang DM gateway controller internal fault

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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.
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BYD DTC AI Analysis

Destroyer 05 ECM hardware fault (data corruption)

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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.
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Other Atto 8 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: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.