A poor or corroded electrical connection at the ABS control module B connector, often caused by water intrusion or road salt.; Damaged, chafed, or open wiring in the CAN bus circuit between the module and the network, frequently near a flex point or a repaired body panel.; A blown fuse or a faulty relay that supplies power to the ABS control module B, which prevents it from waking up and communicating.; A failed ABS control module B itself, either from internal electronics failure or from a cracked circuit board due to heat and vibration.; Low battery voltage or a weak charging system that causes the module to drop offline intermittently, especially during engine cranking.; A network communication fault elsewhere on the CAN bus that disrupts messages to and from the ABS module, such as a shorted bus wire or another module holding the bus down.; Aftermarket accessories or poor previous repairs that tapped into the CAN wiring and introduced interference or a bad splice.

DTC codes / U01xx · Lost communication with a control module / U015A

U015ALost Communication With Anti-Lock Brake System (ABS) Control Module B

U015A means the vehicle's main communication network has lost contact with the anti-lock brake system (ABS) control module designated as 'B', which is typically a secondary or auxiliary ABS module on vehicles with more than one such controller. The computer that stores this code has detected that it is no longer receiving the periodic status messages that module is supposed to broadcast over the controller area network (CAN) bus.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaLost communication with a control module

Symptoms you may notice

The ABS warning light, traction control light, or both illuminate steadily on the dashboard.
The stability control system may be disabled, and the driver may notice a message such as 'Stability Control Off' or 'ABS Unavailable'.
On some vehicles the speedometer, odometer, or cruise control may stop working because wheel-speed data from the ABS module is missing.
The brake pedal may feel normal, but panic stops could lock the wheels if the ABS function is genuinely offline.
Often no symptoms besides the warning light, especially if the primary ABS module still handles base braking and the secondary module is only used for a specific function.
Intermittent warning lights that come and go, particularly over bumps or in wet weather, point to a wiring or connector issue rather than a failed module.

Common causes, most likely first

A poor or corroded electrical connection at the ABS control module B connector, often caused by water intrusion or road salt.
Damaged, chafed, or open wiring in the CAN bus circuit between the module and the network, frequently near a flex point or a repaired body panel.
A blown fuse or a faulty relay that supplies power to the ABS control module B, which prevents it from waking up and communicating.
A failed ABS control module B itself, either from internal electronics failure or from a cracked circuit board due to heat and vibration.
Low battery voltage or a weak charging system that causes the module to drop offline intermittently, especially during engine cranking.
A network communication fault elsewhere on the CAN bus that disrupts messages to and from the ABS module, such as a shorted bus wire or another module holding the bus down.
Aftermarket accessories or poor previous repairs that tapped into the CAN wiring and introduced interference or a bad splice.

How to diagnose and fix it

Verify the battery state of charge and charging system output, then clear the code and test-drive to see whether U015A returns immediately or only intermittently.
Check all fuses and relays that feed the ABS control module B, referring to the vehicle's power distribution diagram, and replace any that are open or intermittent.
Inspect the ABS module B connector for corrosion, water intrusion, bent pins, or a loose latch, and clean or repair as needed.
Perform a voltage drop and resistance test on the CAN bus wires at the module connector, looking for opens, shorts to ground, or shorts to voltage.
Use a scan tool with live data to confirm whether the module appears on the network at all, and check for other communication codes that might point to a shared bus fault.
If wiring and power are good, substitute a known-good module of the same part number or perform a module communication test to confirm the module itself has failed.
After any repair, clear all codes and perform a full drive cycle including ABS activation to verify the fix and ensure no related codes return.

Why the secondary ABS module goes quiet

Many vehicles use two ABS modules, and module B often controls only a specific function such as trailer sway control or a rear-wheel ABS channel, so base braking may feel normal even when the code is set.
A common misdiagnosis is replacing the ABS module when the real fault is a chafed CAN wire inside the wheel well or under the hood, so always inspect the harness before condemning the module.
This code can be set by a weak battery that drops below the module's minimum operating voltage during cranking, leaving no permanent fault in the module itself.
Aftermarket alarms, remote starters, or dash cameras tapped into the CAN bus can disrupt communication and set U015A without any factory component being defective.
On some vehicles, a failing wheel-speed sensor or a damaged tone ring can cause the ABS module to shut down its communication, so check for ABS-specific codes before chasing the network.

Can I keep driving with U015A?

You can usually drive the vehicle with U015A set because base braking remains functional, but the ABS and stability control systems may be disabled, so avoid panic stops and slippery conditions until the fault is repaired. If the brake pedal feels abnormal or the red brake warning light is also on, stop driving and have the vehicle towed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.