U01A2: Lost Communication With Hybrid/EV Battery Interface Control Module C

What it means

Communication with Hybrid/EV Battery Interface Control Module C was not received as expected. This code does not identify the cause or specify the communication network used.

At a glance

• Usually lights the warning light of the system that lost communication
• The engine or gearbox may go into limp mode

How it works

Hybrid/EV Battery Interface Control Module C exchanges battery-system information with other controllers as part of the vehicle's network. U01A2 sets when expected messages from interface module C are not received, and does not by itself identify a battery defect or a fault in modules A, B, or D.

Common causes

Most likely first.

1. Module unpowered
2. Gateway module routing CAN messages incorrectly
3. CAN terminating resistor (120 Ω) drifted out of spec

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Save freeze-frame data and scan the vehicle modules to determine whether module C alone is offline or there are broader battery-network communication faults.
2. Check the instrument panel for battery-system warnings, reduced power, disabled functions, or an inability to enter ready mode.
3. Inspect accessible low-voltage connectors and wiring for interface module C for damage, corrosion, water intrusion, or a loose fit.
4. Check the relevant low-voltage fuse and module power and ground circuits according to the manufacturer's procedure.
5. Have a qualified technician check gateway routing and network integrity, following the manufacturer's safety procedure for any high-voltage interlock checks.

Common fixes

• Repair damaged or corroded accessible wiring or connector terminals at interface module C.
• Restore module C's low-voltage power or ground supply and find the cause of any blown fuse.
• Correct a gateway routing fault affecting module C.
• Repair a confirmed network or interlock fault using the manufacturer's procedure.

Can I keep driving?

Do not drive if a high-voltage warning, reduced propulsion, or abnormal battery behavior appears; the vehicle may limit power or shut down. If no such symptoms are present, arrange prompt diagnosis and keep clear of high-voltage components.