AU
U1004-00

DTC U1004-00 indicates a short to ground in the CAN bus communication circuit of the BYD vehicle's airbag system (SRS) — Qin Plus

Safety System

DTC U1004-00 indicates a short to ground in the CAN bus communication circuit of the BYD vehicle's airbag system (SRS).

In the BYD Qin series network architecture, the SRS ECU communicates in real time with the vehicle control unit, instrument cluster, and other modules via the CAN bus (typically powertrain CAN or body CAN).

If either CAN_H (high line, usually orange/black) or CAN_L (low line, usually orange/brown) shorts to body ground (GND) due to damaged insulation, water corrosion, or mechanical damage, the short pulls the differential bus signal voltage low and prevents normal transmission of communication messages.

This fault forces the SRS system into fail-safe mode, illuminates the airbag warning lamp on the instrument cluster, and prevents proper coordination between the seat belt pretensioners, crash sensors, and airbag deployment circuits.

This creates a severe safety hazard where the airbags fail to deploy during a collision.

5
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Water ingress or terminal corrosion at the SRS ECU wiring harness connector. Water flowing under the center armrest (the common SRS ECU mounting location on the Qin series) after wading, car washing, or a blocked sunroof drain tube shorts the CAN terminals to ground.
  • 2During front-end accident repair or dashboard removal/installation, the metal frame and sheet metal pinched the wiring harness, damaging the insulation and causing the CAN line to contact the body ground point.
  • 3Underbody impact or scraping splits the floor wiring harness sleeve, causing the SRS communication harness to contact a sharp chassis edge and short to ground.
  • 4During non-professional electrical modifications (such as installing a dash cam, ambient lighting, or audio system), fixing screws or cable ties pierce the SRS wiring harness, or splicing wires for power mistakenly grounds the CAN wire.
  • 5Damaged internal CAN transceiver chip in the SRS ECU (e.g., lightning strike, electrostatic breakdown, or power surge), causing the controller's internal CAN port to short to ground.
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 3 minutes for the SRS high-voltage capacitor to fully discharge, preventing accidental airbag deployment.
  • 2
    Fault confirmation: Read the DTC using a BYD VDS or Launch X431 diagnostic tool. Confirm U1004-00 is a current fault and fails to clear. Record the freeze frame data.
  • 3
    Physical inspection: Locate the SRS ECU (typically under the center armrest box or near the gear selector mechanism on Qin 100/Qin EV). Check the wiring harness connector for signs of water ingress, terminal corrosion, or backed-out pins.
  • 4
    Resistance measurement: Disconnect the SRS ECU connector. Use a multimeter to measure the resistance between the harness-side CAN_H (refer to the specific vehicle wiring diagram for the pin number, usually the orange/black wire) and ground. The normal value must be greater than 1 MΩ. Measure the resistance between CAN_L (usually the orange/brown wire) and ground; this value must also be greater than 1 MΩ.
  • 5
    Voltage check: Reconnect the battery, turn the ignition switch to ON (do not start), and measure CAN_H to ground voltage (normal: 2.5-3.5V) and CAN_L to ground voltage (normal: 1.5-2.5V). If the voltage is 0V, confirm a short to ground.
  • 6
    Wiring harness inspection: If resistance is abnormal, inspect the SRS wiring harness section by section along its routing (typically through the floor channel, A-pillar, and instrument panel frame). Check the harness sleeve for wear, especially where it passes moving parts such as door hinges, the steering column, and pedal brackets.
  • 7
    Fault repair: After locating the damage, rewrap the wiring harness with high-temperature fleece tape (avoid PVC tape). Adjust the harness routing to maintain a minimum clearance of 20mm from body metal parts. Repair or replace the damaged connector.
  • 8
    Terminal verification: Measure the resistance between CAN_H and CAN_L (approximately 60Ω, the parallel value of two 120Ω terminating resistors). Confirm no internal short circuit exists in the ECU, then restore the connection.
  • 9
    Clear and test: Clear the fault code, perform a road test on a bumpy road, and confirm U1004-00 does not recur and the airbag warning lamp turns off normally.
Real-World Cases
BYD DTC AI Analysis

Qin EV450 SRS system logged DTC U1004-00 after wading

✓
After driving through standing water, the instrument cluster displayed "Check SRS System" and the airbag warning light stayed on. Scanned with the VDS2000 diagnostic tool and retrieved current fault code U1004-00. Inspection found water pooling beneath the center console. The SRS ECU connector seal deteriorated, and internal terminal oxidation caused a CAN_H short to ground. Dried the wiring harness thoroughly, cleaned the connector terminals with electronic contact cleaner and applied conductive grease, replaced the waterproof seal, and rerouted the drain hose. No recurrence during the one-month follow-up after repair.
BYD DTC AI Analysis

Song MAX CAN network communication fault (similar to U1004-00 symptom)

✓
The vehicle occasionally cut out while driving, with multiple warning lights on the instrument panel. Diagnosis revealed loss of communication between the engine ECU and TCU. CAN bus voltage measurements showed anomalies characteristic of a short to ground. Investigation found a loose bolt on the left-side engine bay ground (G103), causing reference ground potential drift across the entire powertrain CAN network. Several modules logged CAN short-to-ground faults similar to U1004-00. Polished the ground point, applied conductive paste, and tightened the bolt to the specified torque of 10 N·m. Communication returned to normal.
Original source ↗
BYD DTC AI Analysis

Qin 100 U1004-00 DTC After Accident Repair

✓
Minor front collision. After the shop replaced the front bumper and dashboard, the SRS warning light stayed on. Read DTC U1004-00. Found the SRS main harness pinched between the dashboard crossmember and the AC duct bracket during the accident repair. A metal edge cut the insulation, shorting CAN_L to ground. Repair: Released the harness, repaired the wire insulation with heat-shrink tubing, rerouted the wiring per standard procedure, and installed a rubber grommet at the interference point. Fault resolved.
BYD DTC AI Analysis

Aftermarket modifications caused CAN short to ground on Qin 80

✓
After the owner installed an aftermarket 360-degree camera system, the SRS warning light came on. The scan tool showed code U1004-00 and could not clear it. Inspection found the installer had driven self-tapping screws through the firewall to secure the wiring harness, piercing the SRS harness sheath and shorting CAN_H and CAN_L to the body. Repair: Replaced the damaged SRS harness assembly (ECU-to-floor section), removed the self-tapping screws, secured the wiring with proper harness clips, and restored the factory routing.
BYD DTC AI Analysis

BYD Qin EV300 SRS ECU internal fault causing U1004-00

✓
No accident, water damage, or modification history. U1004-00 set suddenly during normal operation. Measured at the SRS ECU connector harness side: CAN_H and CAN_L both exceeded 10MΩ resistance to ground (normal), and harness voltage was normal. Connecting the ECU caused a short to ground at the connector. Diagnosed as a failed internal CAN transceiver chip in the SRS ECU. Replaced the airbag control module (required online coding and crash sensor calibration). Fault completely resolved.
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.