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Home / DTC / U04AC — Invalid Data Received From Hybrid/EV Battery Interface Control Module L

U04AC — Invalid Data Received From Hybrid/EV Battery Interface Control Module L

Detailed page for trouble code U04AC.

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U04AC

Generic U — Network/User

Invalid Data Received From Hybrid/EV Battery Interface Control Module L

Brand: Generic
Type: U — Network/User
Views: UK: 11 EN: 21 RU: 16
AI status
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Page language: EN

Causes

  • Intermittent or open/shorted wiring between the battery interface module and vehicle communication bus (CAN/HS-CAN).
  • Poor connector contact, corrosion, bent pins, or water ingress at the battery interface module harness or junctions.
  • Loss of module power or ground to the battery interface control module.
  • Bus termination or wiring resistance out of tolerance (missing or damaged termination resistor).
  • Module firmware/software mismatch or corrupted software in battery interface module or communicating modules.
  • Electromagnetic interference (high voltage transients) affecting CAN messages.

Symptoms

  • MIL/EV warning lamp illuminated and stored U04AC (or related) fault.
  • Reduced vehicle performance, limited regenerative braking, or limp-home mode.
  • Inability to charge or to start HV system enable sequence.
  • Intermittent electrical faults or multiple communication-related DTCs present.
  • Battery system or HV warnings/messages displayed in vehicle info screens.

What to check

  • Read all U/P codes from all modules and record freeze-frame and snapshot data.
  • Confirm vehicle 12V battery voltage and HV interlock/insulation statuses before probing.
  • Visually inspect connectors, protective boots, and wiring for damage, corrosion, or water entry at the battery interface module and main junctions.
  • Check and wiggle harness while monitoring live data for intermittent changes or communication loss.
  • Measure CAN bus idle voltages at the module connector: CAN_H and CAN_L should both be ~2.5 V (recessive).
  • Measure CAN differential and dominant voltages with a scope: dominant roughly CAN_H ~3.5 V, CAN_L ~1.5 V (differential ~2 V).

Signal parameters

  • Physical bus levels: recessive ~2.5 V on CAN_H and CAN_L (high-speed CAN); dominant ≈ CAN_H 3.5 V / CAN_L 1.5 V (diff ≈ 2 V).
  • Termination resistance: approx. 60 ohms across CAN_H–CAN_L (with ignition off).
  • Typical bus baud rate: manufacturer-specific (commonly 500 kbps or 250 kbps for HS-CAN).
  • Battery interface module CAN messages typically include: pack voltage, pack current, state-of-charge (SOC), cell voltage/imbalance flags, temperature sensors, HV interlock status, insulation monitoring, and a checksum/CRC field.
  • Message frequency and CAN IDs are vehicle-specific; some critical messages are periodic while others are event-driven. Check OEM data for exact IDs and frequencies.

Diagnostic algorithm

  1. Capture and save all diagnostic trouble codes and freeze-frame data from all control modules. Note any other U-codes present.
  2. Clear codes and attempt to reproduce the fault under the same conditions (key on, driving, charging) to confirm persistence and gather timing data.
  3. Perform a detailed visual inspection of the battery interface module connectors, harness sections, and any high-voltage/low-voltage junctions for damage, corrosion, or water contamination.
  4. Verify 12V supply and ground at the battery interface module; repair loose/corroded connections as required.
  5. Check CAN bus electrical integrity: measure idle voltages at the module connector, resistance across CAN_H–CAN_L, and check for short-to-power or short-to-ground conditions on each bus wire.
  6. Use a diagnostic scan tool or CAN sniffer/oscilloscope to monitor CAN traffic from the battery interface module. Look for missing periodic messages, malformed frames, repeated CRC/checksum errors, or bus-off conditions.
  7. If noise or corrupted frames are present, isolate sections of the bus (disconnect branches) to locate the source; repair or replace damaged wiring or connectors found.
  8. If wiring/power/grounds check out and communications remain invalid, verify software/firmware levels on the battery interface module and related control modules; update to OEM revisions if required.
  9. If a suspected module failure remains after all wiring/power/firmware checks, consider module replacement. Re-test and confirm the issue is resolved before finalizing repair.
  10. After repairs, clear all codes and perform a full system relearn or HV system enable/disable sequence per manufacturer procedures, then road-test and re-scan.

Likely causes

  • Damaged connector or wiring harness at the battery interface module (most common).
  • CAN bus voltage levels outside normal range due to short to battery/ground or open circuit.
  • Loose or corroded ground/power connection to the battery interface module.
  • Software communication protocol mismatch after module replacement or update.
  • Failed battery interface module (less common after wiring/power checks).

Fault status

⚠️ Status
Invalid or corrupted data received from Hybrid/EV Battery Interface Control Module (left) — communication/data integrity fault. Check CAN wiring, power/ground, and module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-4 hours

Similar codes

U0100 U0073 U0416 U0140
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