U016A – Lost Communication With Brake System Control Module

System: Network | Standard: ISO/SAE Controlled | Fault type: General

Definition source: SAE J2012/J2012DA (industry standard)

DTC U016A indicates that one or more modules on the vehicle network are reporting a loss of communication with the Brake System Control Module. In practical terms, the rest of the vehicle can no longer reliably exchange messages with that brake-related controller over the data bus, so related functions may be limited or disabled as a precaution. The exact set of affected features, warning indicators, and whether the fault is intermittent or hard depends on how the vehicle is engineered and what network architecture it uses. Always confirm the module locations, network topology, fuses, grounds, and diagnostic routines in the applicable service information before making repair decisions.

What Does U016A Mean?

U016A – Lost Communication With Brake System Control Module means the vehicle has detected that expected network messages from the Brake System Control Module are missing or invalid for a calibrated period of time. SAE J2012 defines the structure of DTCs, and “U” codes generally relate to network communication issues rather than a single sensor signal being high, low, or out of range. This code does not, by itself, prove that the brake control module has failed; it only confirms that the communication path to that module is not functioning as expected. The root cause can be within wiring, connectors, power/ground supply, the network itself, or the module.

Quick Reference

• Subsystem: Vehicle network communication with the Brake System Control Module
• Common triggers: Module offline, missing network messages, bus interference, poor power/ground to the module, connector/wiring faults
• Likely root-cause buckets: Wiring/connector issues, network faults, power/ground supply problems, module internal fault, configuration/software issues (varies by vehicle)
• Severity: Potentially high; brake-related functions may be reduced and warning indicators may illuminate
• First checks: Scan for multiple network DTCs, verify battery/charging health, check related fuses/grounds, inspect connectors and harness routing to the module
• Common mistakes: Replacing the module before verifying power/ground and network integrity, ignoring other U-codes that indicate a broader bus problem

Theory of Operation

The Brake System Control Module typically communicates with other controllers over the vehicle network to share status and requests related to braking functions. Other modules expect to receive periodic messages (and may also request data) so they can coordinate features and illuminate warnings when needed. The network uses a shared communication pair (varies by vehicle) with multiple modules connected; message timing, IDs, and validity checks are used to determine whether communication is healthy.

U016A is set when one or more modules determine that the Brake System Control Module is not communicating as expected. This can happen if the module loses power or ground, if the network wiring is open/shorted or has high resistance, if a connector has poor terminal contact, or if network traffic is disrupted. Some vehicles will log additional U-codes pointing to a specific bus segment or multiple modules dropping offline at once.

Symptoms

• Warning lights: Brake-related warning indicators illuminated
• ABS/traction status: ABS/traction or stability-related functions limited or disabled (varies by vehicle)
• Driver messages: “Service brake system” or communication-related messages on the information display (varies by vehicle)
• Intermittent behavior: Symptoms that come and go with vibration, temperature changes, or moisture
• Stored codes: Multiple network (U) codes present in several modules
• Scan tool access: Brake System Control Module not responding to scan tool requests, or responding intermittently

Common Causes

• Open, shorted, or high-resistance wiring in the network communication circuits between modules (varies by vehicle network design)
• Loose, corroded, backed-out, or damaged terminals at the brake system control module connector or at intermediate network connectors/splices
• Power supply issue to the brake system control module (blown fuse, faulty relay, poor power feed connection)
• Ground circuit problem for the brake system control module (loose ground fastener, corrosion, damaged ground wire) causing module reset or dropout
• Short to power or short to ground on a network line due to chafing, pinched harness, or water intrusion affecting the harness/connector
• Another control module or accessory on the same network segment pulling the bus down or disrupting messaging (network-wide fault)
• Intermittent module reset from unstable system voltage (charging system concern or high-resistance main connections)
• Brake system control module internal fault (hardware/software), considered after power/ground and network integrity are verified

Diagnosis Steps

Tools that help: a scan tool capable of full-vehicle network scans and live-data logging, a digital multimeter for continuity and voltage-drop testing, and basic backprobing/pin-testing supplies. Service information is needed for connector pinouts, fuse/relay identification, network topology, and approved test points. A battery/charging system tester is useful when resets or low system voltage are suspected.

1. Confirm the code and capture context. Run a full scan and record U016A plus any additional network, power supply, or brake-related codes. Save freeze-frame or “event” data if available. Multiple communication codes often indicate a shared power/ground or network issue rather than a single module failure.
2. Check scan tool communication with the brake system control module. Attempt to enter the module directly. Note whether the module is completely non-responsive, intermittently responsive, or responsive with stored history codes. This observation guides whether to focus first on power/ground (no response) or network integrity/intermittent issues (intermittent response).
3. Assess vehicle warnings and baseline operation. Note any brake/traction/stability warnings and whether they change with key cycles. If the vehicle indicates reduced braking assist or multiple safety warnings, prioritize a stationary diagnosis and avoid road testing until basic checks are completed.
4. Inspect battery and main connections first. Verify battery terminals are clean and tight and inspect main ground points and high-current connections for looseness or corrosion. Perform voltage-drop testing on key power and ground paths under electrical load (headlamps, blower, rear defrost) to identify excessive resistance that can cause module dropouts or resets.
5. Verify module power feeds and grounds. Using service information, locate the brake system control module fuses/relays and confirm they are intact and properly seated. With the connector(s) accessible, check for the presence of the required power supply feeds and solid grounds at the module. If power/ground is missing or unstable, diagnose that circuit before any network testing.
6. Perform a focused visual and physical inspection of the harness. Inspect the brake system control module connector(s), nearby harness routing, and any known splice/junction areas for pinched sections, rubbing/chafing, prior repair, or signs of moisture/corrosion. Look for terminal damage such as spread pins, pushed-out terminals, or poor pin fit.
7. Wiggle test for intermittent dropouts. With the scan tool connected and live data/communication status displayed (or with a continuous module ping), gently move the harness and tap connectors along the suspected path. If communication drops in/out or additional network codes set during movement, isolate the exact area that triggers the fault.
8. Network integrity checks at the connector. With the ignition state set as directed by service information, test the network circuits for continuity and for shorts to power or ground. If the network uses paired lines, check for damage affecting either line and confirm there is no unwanted continuity between the lines where it should not exist (refer to service procedures for the correct method).
9. Isolate a bus disruptor if the issue appears network-wide. If multiple modules show “lost communication” or the scan tool intermittently loses connection, isolate by disconnecting suspected devices/branches one at a time as allowed by service procedures, then re-check network stability. This can help identify a module or harness branch that is pulling the network down.
10. Compare live data and status across modules. Use the scan tool to monitor network status indicators and related brake/vehicle dynamics parameters that other modules may broadcast/receive (names vary by vehicle). Log data during key cycles and during a controlled wiggle test to correlate the exact moment the brake module drops offline.
11. After repairs, verify with a full network scan and road test as appropriate. Clear codes, cycle the key, and confirm the brake system control module remains reachable and U016A does not reset. Re-scan all modules for pending codes. If safe and permitted, perform a short road test while logging data to confirm communication remains stable under vibration and load.

Professional tip: If the brake system control module is completely unreachable, treat it like a power/ground or connector/terminal problem until proven otherwise. Prove stable power and ground at the module with voltage-drop testing under load, then prove the network circuits are not shorted or open. Replacing a module before validating these basics often results in a repeat U016A because the underlying dropout condition remains.

Possible Fixes & Repair Costs

Repair costs for U016A vary widely because the underlying cause can range from a simple connection issue to a module power/ground problem or network wiring fault. Parts, labor time, and diagnostic effort depend on vehicle design and what testing confirms.

• Clean, reseat, and secure the brake system control module connector(s); repair terminal fit issues found during inspection
• Repair or replace damaged network wiring (twisted pair where applicable), including chafed sections, pinched harnesses, or corrosion-related conductor damage
• Restore module power supply and ground integrity by repairing open circuits, high resistance, poor grounds, or fuse/relay/connector issues verified by testing
• Correct improper harness routing or strain that causes intermittent opens/shorts; add proper retention where missing
• Repair water intrusion sources and address corrosion at connectors or splices after confirming they affect communication
• Reprogram/configure the brake system control module or related network modules if service information directs and diagnostics indicate a software/configuration issue
• Replace the brake system control module only after confirming power/grounds and network circuits are correct and communication loss is isolated to the module

Can I Still Drive With U016A?

Use caution. U016A indicates the network lost communication with the brake system control module, which can affect brake-related functions and warning indicators depending on vehicle design. If brake, stability/traction, or ABS warnings are present; if the pedal feel changes; or if any safety-related messages appear, do not drive and arrange for diagnosis and towing. If the vehicle seems normal, drive only as needed to reach a safe location or repair facility, and avoid high-speed or low-traction conditions.

What Happens If You Ignore U016A?

Ignoring U016A can lead to intermittent or persistent loss of brake-related features that rely on module communication, repeated warning lights, and reduced system redundancy. A communication problem may worsen over time if caused by corrosion, wiring damage, or poor terminal tension, potentially leaving you without driver-assist brake functions when you need them.

Last updated: March 16, 2026

Vehicles Commonly Affected by U016A

• Vehicles using a networked brake control architecture where brake functions communicate over the vehicle bus
• Vehicles with integrated stability control/traction control that relies on brake module network messaging
• Vehicles with multiple chassis control modules sharing data on the same communication network
• Vehicles exposed to moisture, road salt, or humidity that can accelerate connector and splice corrosion
• Vehicles with prior collision repair, harness repairs, or aftermarket electrical work near chassis wiring
• High-mileage vehicles where connector terminal tension and ground integrity may degrade over time
• Vehicles with wiring routed near heat sources or moving components that can chafe or pinch the harness
• Vehicles that have recently had battery, fuse box, or ground point service that could introduce connection issues

Always confirm the final repair by verifying stable network communication with the brake system control module using a scan tool and by rechecking for returning codes after an appropriate drive cycle.