U01AA: Lost Communication With Hybrid/EV Battery Interface Control Module K

What it means

Communication with Hybrid/EV Battery Interface Control Module K 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 K exchanges battery-system information with other vehicle modules over a communication network. The vehicle sets U01AA when expected messages from module K are missing; the code does not establish whether module K, its power supply, the gateway, or the network is at fault.

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. Record all codes and freeze-frame data, noting whether U01AA appears with other lost-communication codes that could point to a shared power or network problem.
2. Use a scan tool that supports the vehicle to check whether module K responds and compare its status with the other battery interface modules.
3. Inspect module K's accessible connectors and wiring for looseness, corrosion, damage, or signs of water intrusion.
4. Check the power and ground circuits serving module K using the vehicle wiring information and the manufacturer's specification.
5. If power and ground are sound, have the relevant network wiring, gateway message routing, and CAN termination checked against the manufacturer's specification.

Common fixes

• Reconnect or repair a loose, corroded, or damaged module K connector.
• Repair a damaged power, ground, or communication wire serving module K.
• Correct a confirmed module K power or ground supply fault.
• Repair a verified gateway routing or CAN termination fault.
• Replace module K only if testing confirms it is faulty and the manufacturer's service information supports replacement.

Can I keep driving?

Because missing battery-system communication can trigger reduced-power operation or shutdown, avoid relying on the vehicle for routine or long-distance travel if warnings or drivability changes are present. Stop in a safe place if propulsion or other essential functions become unreliable, and arrange diagnosis.