U04AC

Code

Generic U — Network/User

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

Brand: Generic

Type: U — Network/User

Views: UK: 20 EN: 29 RU: 27

AI status

Completed

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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

Capture and save all diagnostic trouble codes and freeze-frame data from all control modules. Note any other U-codes present.
Clear codes and attempt to reproduce the fault under the same conditions (key on, driving, charging) to confirm persistence and gather timing data.
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.
Verify 12V supply and ground at the battery interface module; repair loose/corroded connections as required.
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.
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.
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.
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.
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.
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