U04B1

Code

Generic U — Network/User

Invalid Data Received From Battery Monitor Module

Brand: Generic

Type: U — Network/User

Views: UK: 34 EN: 163 RU: 92

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Faulty or intermittent CAN/LIN communication between BMM and other modules
Corroded, loose, damaged or disconnected connectors/wiring at the battery monitor or junctions
BMM power or ground supply fault (low supply voltage, open ground, blown fuse)
Battery cells or sensor faults inside the battery pack producing invalid readings
Software/calibration mismatch, corrupted module software, or incompatible replacement module
Electromagnetic interference (EMI) or short to battery/ground on communication lines

Symptoms

Battery/charging system warning lamp or MIL illuminated
Incorrect state-of-charge (SOC) or range displayed
Reduced charging or limp-home mode depending on vehicle
Battery pack or cell voltage/temperature readings missing, erratic or out-of-range on scan tool
No cranking or start issues if 12V battery monitored and allowed to discharge
Loss of linked functions that rely on BMM data (regenerative braking, energy management, HVAC limitations)

What to check

Read all related U-codes and freeze frame data with a capable scan tool; record BMM message values and timestamps
Verify vehicle battery (12 V) resting voltage and while cranking/vehicle ON; check for low supply
Visually inspect BMM connector(s), wiring harness, and battery pack connections for damage, corrosion, water ingress, or loose pins
Check fuses and ground points for the BMM and battery management circuits
Use a scope or CAN bus tester to verify CAN-H/CAN-L differential signals and message traffic while reproducing the fault
Check termination resistors (≈120 ohm across CAN H/L) and for shorts to battery or ground on communication lines

Signal parameters

BMM pack voltage — should match measured pack voltage (vehicle-dependent; e.g., ~12–15 V for 12V systems, or manufacturer HV pack nominal voltage for HV systems)
BMM pack current — should reflect charging/discharging current and not be erratic (range depends on vehicle)
Cell voltages — individual cell voltages within expected cell range (typical 2.5–4.2 V per cell for lithium chemistries)
State of Charge (SOC) — expected 0–100% and consistent with pack voltage and state
Temperature sensors — cell/pack temps within sensor operating range (typical -40 to +125 °C) and consistent with ambient/pack heating
CAN bus idle differential — ≈0 V differential when inactive, ~2.5 V common-mode; active frames show expected differential pulses

Diagnostic algorithm

Connect a scan tool and note all U-codes and BMM data fields (pack voltage, cell voltages, SOC, temps). Capture freeze frame if available.
Verify basic power and ground: measure 12 V battery voltage and BMM supply and ground pins with key ON/OFF. Repair low supply or bad ground before further testing.
Visually inspect connectors, harness and junctions for damage, corrosion, water intrusion or bent pins; repair as required.
With the engine/vehicle ON, use an oscilloscope or CAN bus analyzer to check CAN-H/CAN-L signal integrity at the BMM connector and at a known-good node. Look for missing messages, noise, or incorrect voltages.
Check for proper bus termination (≈120 ohm between CAN H and CAN L). Repair wiring faults, shorts to power/ground or opens.
Compare the BMM reported voltages/temps to independent measurements on the pack (only by qualified personnel for HV systems). If readings differ significantly, suspect BMM sensor or module fault.
If wiring and power/grounds are good and bus traffic is valid but data values are implausible, check for software updates or calibration level mismatches and perform reflash/update if available.
If still unresolved, attempt to reproduce code with a known-good BMM (if available) or swap with a reconditioned/bench-tested unit per manufacturer procedure. Replace BMM if confirmed faulty.
After any repair, clear codes and perform road test or operational checks to confirm U04B1 does not return. Document findings and repairs.

Likely causes

Open/short/intermittent CAN bus wiring or connector at BMM
Low battery or poor ground causing corrupted data from BMM
BMM itself producing invalid cell/pack values due to internal fault
Module communication timeout or message checksum/frame errors
Recent module replacement or software update with incorrect calibration

Fault status

⚠️ Status

Invalid data received from Battery Monitor Module (BMM). Possible communication error, wiring/power fault, or BMM malfunction. Verify battery voltage, connectors, and CAN/LIN communications.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5-3.0 hours