U01A1

Code

Generic U — Network/User

Lost Communication With Hybrid/EV Battery Interface Control Module B

Brand: Generic

Type: U — Network/User

Views: UK: 21 EN: 32 RU: 27

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open or short in CAN/CAN-FD data lines between BCM/TCU and Battery Interface Control Module B
Loss of module power (12V feed, ignition-switched power) or ground to the Battery Interface Control Module B
Faulty Battery Interface Control Module B (internal failure)
Blown fuse or relay supplying the battery interface module
Corroded, loose, or damaged connector at the module or harness
Network termination resistor missing or shorted, bus wiring short to chassis or battery

Symptoms

Hybrid/EV system disabled or fails to engage
Reduced power, limp-home mode or EV mode unavailable
Malfunction Indicator Lamp (MIL) or hybrid system warning displayed
Stored DTCs relating to charging, battery management, or vehicle control modules
Inability to start or drive in expected modes
Instrument cluster messages indicating communication loss with battery module

What to check

Use a compatible scan tool to read all network controllers and confirm U01A1 and any related codes or freeze frame data
Check for presence of Battery Interface Control Module B in the vehicle network (module list) via scan tool
Inspect fuses and relays supplying the battery interface module
Visually inspect module connector and harness for corrosion, damage, or moisture
Measure module supply voltage (12V) and ground integrity at the module harness
Measure CAN High and CAN Low voltages at the module connector with ignition ON (see signal parameters)

Signal parameters

CAN/CAN-FD idle voltages: CANH ≈ 2.5 V, CANL ≈ 2.5 V (recessive); dominant state: CANH ≈ 3.5 V, CANL ≈ 1.5 V
Typical CAN differential when dominant: ≈ 2.0 V
Resistance across CANH and CANL with network connected: ≈ 60 ohms (two 120 ohm terminators in parallel)
Module 12V supply (battery/ignition feed): ≈ 11–14 V (with ignition ON)
Module ground continuity: near 0 ohms to chassis ground

Diagnostic algorithm

Connect a scan tool and read U01A1 plus any other active or stored codes. Note freeze frame/conditions when the fault set.
Attempt to communicate with Battery Interface Control Module B via the scan tool. If module not present, proceed to wiring/power checks.
Inspect related fuses/relays and verify 12V supply and ground at the module connector. Repair any open circuits or poor grounds.
Visually inspect the module connector and harness for damage, corrosion, water ingress, or pin damage. Repair as required.
With ignition ON, measure CANH and CANL at the module connector. Compare to expected idle voltages and check differential during communication attempts.
Check bus termination resistance (≈60 ohms). If abnormal, isolate and inspect modules or terminators on that segment.
Use a CAN bus analyzer or oscilloscope to observe traffic and error frames. Look for repeated retransmissions, error counters, or absence of messages from the module.
Perform a wiggle test on the harness while monitoring the bus to locate intermittent faults. Repair wiring or connectors as found.
If wiring, power, and termination are good but module remains unresponsive, update module software per manufacturer procedures if available, then re-test.
Replace Battery Interface Control Module B only after confirming module is non-communicative and wiring/power/termination are good. Follow all high-voltage and manufacturer safety procedures when handling hybrid/EV components.

Likely causes

Damaged or disconnected CAN high/low wiring to Battery Interface Control Module B
No 12V supply or poor ground to the battery interface module
Connector corrosion or bent pins at the module connector
Failed Battery Interface Control Module B
Blown fuse in the module power circuit

Fault status

⚠️ Status

Lost Communication With Hybrid/EV Battery Interface Control Module B — the module did not respond or messages from it were not detected on the vehicle communication bus (CAN/CAN-FD).

🔴 Repair difficulty: Hard

⏱️ Diagnostic time: 1.5-3.0 hours