AU
U040100

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

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 Seal U indicates invalid data received from the Engine Control Module by the brake system over the CAN network. This is a medium-severity fault that may reduce regenerative braking, ESC function, or brake pedal feel. Common causes include poor ECM power or ground connections, or a CAN 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.
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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Poor contact in the ECM power supply/ground circuit: a loose fuse connection or oxidized/loose ground points G101/G102 cause unstable ECM operating voltage, resulting in the ECM sending corrupted data frames.
  • 2Powertrain CAN bus physical layer fault: Short or open circuit in the twisted pair between the ECM and gateway, terminal resistor drift (normal: 60Ω), or oxidized connector pins (e.g., water ingress at the 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: Burnt internal gateway PCB capacitor or 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 of U040100 and the environmental conditions during occurrence (e.g., accompanying communication faults like U0100). Check the instrument panel warning light status. Confirm if the vehicle experiences limited power or abnormal braking.
  • 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 must be 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 60 Ω; if abnormal, check the ECM or gateway terminating resistor). Check the CAN lines for short circuits to ground or power. Inspect 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'. 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 with the latest BYD TIS version bulletin to check for 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 CAN resistance changes to locate the faulty module. Install a known-good gateway or ECM for swap testing. If the fault transfers, the corresponding module is defective. 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

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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.
Original source ↗
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.
Original source ↗
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.
Original source ↗
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.
Original source ↗
Other Seal U Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.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.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.