U015A: Lost Communication With Anti-Lock Brake System (ABS) Control Module B

What it means

ECU lost CAN communication with the secondary ABS control module B. A communication loss with this module breaks any function relying on its data — diagnostic tools may show 'no response' and dependent modules can fall into limp 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

ABS Control Module B is a secondary anti-lock brake system controller that communicates brake-related information over the vehicle network. U015A sets when the reporting module does not receive the expected messages from this specific ABS module for the required time; other modules may then lose functions that depend on its data.

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, not just the engine controller, to identify which ones report U015A, check for other lost-communication codes, and review freeze-frame data for low voltage.
2. Check battery condition and charging-system operation before tracing network faults, because low voltage can make multiple modules drop offline.
3. Inspect ABS Control Module B's power and ground connections, fuses, and network connector for a loss of supply, corrosion, or damaged wiring.
4. Use a scan tool to check whether ABS Control Module B responds and note any ABS or brake warnings and affected functions.
5. If its power and ground are sound, test the CAN wiring and gateway communication path for opens, shorts, or routing faults.
6. If the network path is intact, test the CAN termination only as specified by the vehicle manufacturer and investigate the module itself.

Common fixes

• Restore battery charge or repair the charging-system fault.
• Repair a blown supply fuse or poor power or ground connection to ABS Control Module B.
• Repair damaged CAN wiring or connector terminals, or correct a verified gateway routing fault.
• Repair the CAN termination fault if testing confirms it is outside the manufacturer's specification.
• Repair or replace ABS Control Module B if its supplies and network path are sound.

Can I keep driving?

Treat this as a brake-system warning: drive only as needed to reach a safe place, avoid high speeds and hard braking, and do not rely on ABS or related assistance until checked. If braking feels abnormal or a brake warning appears, stop safely and arrange recovery.