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Home / DTC / U01A8 — Lost Communication With Hybrid/EV Battery Interface Control Module I

U01A8 — Lost Communication With Hybrid/EV Battery Interface Control Module I

Detailed page for trouble code U01A8.

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U01A8

Generic U — Network/User

Lost Communication With Hybrid/EV Battery Interface Control Module I

Brand: Generic
Type: U — Network/User
Views: UK: 12 EN: 26 RU: 16
AI status
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Page language: EN

Causes

  • Battery Interface Control Module (BICM) failed or software crashed
  • Loss of module power (12 V or internal supply) or poor ground
  • Open/short/low integrity in CAN/LIN communication wiring or connector
  • Blown fuse or faulty relay supplying the module
  • Improper bus termination, missing resistor or short to chassis
  • High-voltage pack service disconnect/open interlock preventing module operation

Symptoms

  • Hybrid/EV warning lamp or MIL illuminated
  • No battery pack data (voltage, current, SOC) available on scan tool
  • Reduced propulsion or hybrid system in limp/reduced-power mode
  • Inability to start or enable HV system
  • Multiple modules reporting communication loss or network errors
  • Intermittent loss of charging or regenerative braking data

What to check

  • Use a capable scan tool to confirm U01A8 and list all communication-related U-codes; note freeze frame and occurrence conditions
  • Confirm presence/absence of the BICM in the scan tool module list and check firmware/calibration version
  • Visually inspect wiring and connectors to the battery interface module for corrosion, damage, or water intrusion
  • Check fuses and relays that supply the module for continuity and correct operation
  • Measure module supply voltage (expected ~11–14 V when key on/run) and verify a low-resistance ground
  • Measure CANH/CANL idle voltages and check for proper termination resistance (~60 ohms across CANH–CANL with key on, network powered)

Signal parameters

  • CAN idle: CANH ≈ 2.5 V (recessive); CANL ≈ 2.5 V (recessive); dominant: CANH ≈ 3.5 V, CANL ≈ 1.5 V
  • Typical dominant differential ~1.5–2.5 V during frames
  • Termination resistance: ~60 ohms measured across CANH–CANL with power on
  • Module supply (12 V): nominal 11–14 V (key on/run); ground resistance preferably
  • Possible bus speeds: 125 kbps / 250 kbps / 500 kbps (confirm vehicle-specific)
  • Message frequency: battery interface telemetry typically 10–1000 ms depending on parameter (verify expected message IDs and rates)

Diagnostic algorithm

  1. Safety first: follow vehicle manufacturer high-voltage and battery isolation procedures before performing in-depth work. Wear required PPE.
  2. Connect a dealer-level or advanced scan tool. Record U01A8 and any related codes, freeze-frame data, and module list. Note whether the BICM appears on the tool.
  3. Clear codes and attempt to reproduce. If code returns, proceed. If intermittent, try ignition cycles and bus activity tests.
  4. Verify basic power/ground: check 12 V supply and ground at the BICM connector with the harness connected. Repair any open/poor circuits.
  5. Inspect connectors and wiring harness for physical damage, corrosion, or water intrusion. Repair or replace damaged connectors/wires.
  6. Check fuses/relays supplying the module. Replace any blown fuses and test relays for proper operation.
  7. Measure CAN bus: with key on, measure CANH/CANL idle voltages, and measure resistance across the two lines (≈60 Ω). Use an oscilloscope or CAN logger to verify expected messages and bus speed. Identify missing message IDs from the BICM.
  8. If bus is silent or shows bus-off, locate the offending branch or module by disconnecting segments/connectors one at a time while monitoring bus activity until normal operation returns.
  9. Verify HV interlocks and service disconnect status; correct any open interlock that prevents the BICM powering up.
  10. Check for software/calibration mismatches: compare module software level to vehicle service info. Reprogram or update if required.
  11. If wiring, power, and gateway function are good and the BICM still does not communicate, consider bench-testing or replacing the battery interface module per OEM procedure. After replacement, program and relearn as required.
  12. After repairs, clear codes and perform a full system check. Confirm normal communication, no recurrence, and proper hybrid/EV system operation.

Likely causes

  • Disconnected/damaged CAN connector at the battery interface module
  • Blown 12 V fuse or bad relay feeding the module
  • CAN bus shorted to battery or ground at a harness chafing point
  • Battery pack interlock/open safety contact preventing module power-up
  • Failed battery interface module requiring replacement or reflash
  • Gateway/module software version mismatch blocking communication

Fault status

⚠️ Status
Lost Communication With Hybrid/EV Battery Interface Control Module I — the vehicle network reports the battery interface module is not responding or its messages are not present. Verify wiring, power, and module status.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-4.0 hours

Similar codes

U0073 U0100 U0121 U0140 U0299
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