U01AF: Lost Communication With Hybrid/EV Battery Interface Control Module P

What it means

Communication with Hybrid/EV Battery Interface Control Module P 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 P exchanges battery-system data with other controllers over the vehicle network. This code sets when expected messages from module P are missing; it does not identify which network path failed.

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. Scan all modules for communication codes and note freeze-frame data to see whether other controllers on the same network also went offline.
2. Check whether module P responds to a scan tool and whether its battery-system data is available.
3. Inspect module P's connectors and wiring for looseness, corrosion, damage, or signs of water entry.
4. Check the module's power and ground circuits under load against the manufacturer's specification.
5. If power and ground are sound, have the relevant network wiring and gateway message routing checked for opens, shorts, or termination faults.

Common fixes

• Reconnect or repair a loose, corroded, or damaged module P connector.
• Repair damaged wiring or restore the module's power or ground supply.
• Repair a fault in the applicable network wiring or gateway routing.
• Replace module P if it remains unresponsive with verified power, ground, and network connections.

Can I keep driving?

Because this fault can affect hybrid battery functions and may trigger reduced-power operation or shutdown, avoid relying on the vehicle for a long trip. Stop safely if power delivery becomes abnormal or warnings indicate a hybrid-system problem.