U025E: Lost Communication With Electronic Brake Booster Control Module A

What it means

A control module has stopped receiving expected messages from electronic brake booster control module A. Brake-assist behavior may be affected; the code alone does not establish the resulting braking mode.

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

Electronic brake booster control module A communicates with other modules to coordinate brake assist and related functions. U025E sets when a monitoring module does not receive the expected messages from that brake booster module; the code alone does not show what braking mode the vehicle has entered.

Common causes

Most likely first.

1. Bus wiring open or shorted
2. Module without power or ground
3. Module failed

Symptoms

• A brake-system warning may appear
• Brake assist or related functions may be limited

How to diagnose it

1. If the brake warning is on or pedal effort or braking behavior has changed, stop in a safe place and do not continue driving until the vehicle is assessed.
2. Record freeze-frame data and scan all modules for brake and communication codes to identify related faults alongside the loss from booster control module A.
3. Inspect module A's connectors and bus wiring for loose or corroded terminals, damaged wires, or signs of a short or open.
4. Check the brake booster control module's power and ground circuits using the manufacturer's procedure, because loss of supply can disable communication and affect assist.
5. If the supplies are correct, test the network wiring to module A for opens or shorts according to the manufacturer's procedure.

Common fixes

• Reconnect a loose connector at electronic brake booster control module A.
• Repair damaged or corroded network wiring and connector terminals serving module A.
• Restore a missing power or ground connection to the brake booster control module.
• Replace module A if its power, ground, and network wiring are correct but it still does not communicate.

Can I keep driving?

Treat this as a potentially safety-critical fault: if a brake warning appears, the pedal feels abnormal, or braking changes, stop safely and arrange recovery rather than continuing to drive. Reduced brake assist can increase pedal effort, and braking performance may be affected.