U01A4

Code

Generic U — Network/User

Lost Communication With Hybrid/EV Battery Interface Control Module E

Brand: Generic

Type: U — Network/User

Views: UK: 22 EN: 37 RU: 24

AI status

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Page language: EN

Causes

Battery interface control module E powered down or failed
Blown fuse or opened relay supplying module power
Poor or missing ground at the module
Damaged, corroded, or disconnected connector/wiring between the module and vehicle network
CAN bus shorted to battery voltage or ground, or open circuit
Missing or incorrect bus termination resistor

Symptoms

Battery/HEV system warning lights or messages on dash
Reduced or disabled hybrid/EV functionality (limited charge/discharge, limp mode)
Inability to read battery interface E data with the scan tool
Other modules reporting related COMM U-codes or battery-related DTCs
Vehicle may not start/drive normally if battery control is lost

What to check

Use a scan tool to confirm U01A4 and list other network DTCs; attempt to communicate directly with module E
Visually inspect module E connector and harness for corrosion, damage, or water ingress
Check fuses and relays supplying module E and measure module supply voltage with key on
Verify good ground(s) at the module mounting/ground point
Measure CAN_H/CAN_L voltages at module connector with key ON (KOEO) and engine off
Check bus termination resistance (approx. 60 ohm across CAN_H and CAN_L for two 120Ω in parallel)

Signal parameters

CAN bus nominal recessive voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (key ON, no traffic)
CAN dominant voltages during frames: CAN_H ≈ 3.5–3.9 V, CAN_L ≈ 0.9–1.3 V (values vary by vehicle)
Bus differential dominant amplitude ≈ 2.0–3.0 V
Typical CAN baud rates used on EV/HV subsystems: 250 kb/s or 500 kb/s (verify vehicle-specific)
Expected periodic messages from battery interface modules (SOC, pack voltage, current, temperature) — message intervals commonly 100–1000 ms
Termination resistance across CAN_H and CAN_L ≈ 60 Ω (two 120 Ω resistors in parallel)

Diagnostic algorithm

Record freeze-frame data and all U-codes from all modules. Note whether module E is present in network topology.
Attempt to communicate with Battery Interface Control Module E using an OEM-capable scan tool. Note any response or lack thereof.
Inspect module E connector and harness for physical damage, water intrusion, bent pins, or corrosion. Repair or clean as needed.
With key ON (engine off) and following HV safety procedures, verify module supply voltage at the module connector and check related fuses/relays. Replace blown fuses or faulty relays.
Verify module ground(s) for low resistance to chassis (use a DVOM). Repair poor grounds.
Measure CAN_H and CAN_L at the module connector: confirm idle voltages and that dominant/recessive levels occur when bus is active. If voltages are incorrect, isolate sections of the bus to find short/open.
Check termination resistance across CAN_H and CAN_L at multiple points. Replace missing/damaged termination resistors.
If one node is suspected, disconnect the module (or suspected interfering module) and observe whether bus returns to normal and communication is restored. Use caution and follow procedures for disconnecting HV-related modules.
If wiring and bus appear good but module does not respond, attempt software reflash or module reset per manufacturer procedures. Reprogram only with correct calibration files.
If module still fails to communicate after power/ground/wiring verification and reflashing, consider replacing the battery interface control module and recheck network for faults.
After repair, clear codes and perform functional test/road test to confirm resume of normal communication and restore EV/HV system operation.