U018A – Lost Communication With Audio/Video Module “B”

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

Definition source: SAE J2012/J2012DA (industry standard)

U018A indicates that one or more modules on the vehicle network have detected a loss of communication with Audio/Video Module “B”. In practical terms, the vehicle expects to exchange messages with that module over the communication bus, and the expected data is missing for long enough to be considered a fault. This is a network-type DTC, so the underlying issue is often related to module power/ground, bus wiring integrity, connector quality, or a module that is not awake or not responding. DTC behavior, set conditions, and naming of “Module B” vary by vehicle, so confirm module location, network topology, and test points using the correct service information before starting repairs.

What Does U018A Mean?

U018A – Lost Communication With Audio/Video Module “B” means the vehicle has detected that it can no longer communicate with the Audio/Video Module “B” on the network. SAE J2012 defines the structure and general intent of U-codes as network communication faults, where modules share data over a serial bus. This DTC does not, by itself, prove the audio/video unit is failed; it indicates that expected network messages from that specific module are not being received (or cannot be understood) within the monitor’s criteria. Root cause must be confirmed with network, power/ground, and wiring checks specific to the vehicle.

Quick Reference

• Subsystem: Vehicle communication network (bus) link to Audio/Video Module “B”.
• Common triggers: Module “B” offline, loss of power/ground to the module, bus open/short, poor connector contact, or module reset.
• Likely root-cause buckets: Wiring/connector issues, power/ground faults, network bus faults, module internal fault, configuration/software (varies by vehicle).
• Severity: Usually comfort/infotainment related, but may affect other features that rely on shared network data; driveability impact varies by vehicle.
• First checks: Scan for companion U-codes, confirm module presence on the scan tool, check module fuses/feeds/grounds, inspect network connectors and harness routing.
• Common mistakes: Replacing the module before verifying power/ground and bus integrity, ignoring low battery/voltage events, or overlooking a loose connector/pin-fit issue.

Theory of Operation

Modern vehicles use a serial communication network so modules can share status and commands. The Audio/Video Module “B” typically broadcasts and/or responds to periodic messages, and other modules (or a central gateway) monitor the presence and validity of these messages. If the expected messages stop arriving, arrive corrupted, or the module does not respond to directed requests, the monitoring module flags a loss-of-communication condition and stores U018A.

A communication loss can occur if the module is powered down unexpectedly, has an unstable ground, is stuck during initialization, or the network wiring is disrupted. Bus faults can include opens, shorts between bus circuits, shorts to power/ground, excessive resistance at terminals, or poor shielding/routing that degrades signal quality. The exact monitor timing and which controller sets the code vary by vehicle, so service information is essential.

Symptoms

• Infotainment: Audio/video screen may be blank, frozen, rebooting, or non-responsive.
• Sound: No audio output, intermittent audio dropouts, or loss of certain audio sources/features.
• Controls: Steering-wheel or console media controls may not function or respond slowly.
• Messages: Warning message or feature-unavailable notice related to audio/video functions (wording varies by vehicle).
• Connectivity: Loss of connected features that depend on the audio/video module interface (availability varies by vehicle).
• Intermittent: Symptoms may appear over bumps, during temperature changes, or after a restart if a connection is marginal.

Common Causes

• Open circuit, short-to-ground, or short-to-power on the network communication wiring between the main network and the Audio/Video Module “B” (varies by vehicle network layout)
• High resistance or intermittent connection at the Audio/Video Module “B” connector (loose terminal fit, fretting, partial unplug, pin push-out)
• Power feed issue to the Audio/Video Module “B” (blown fuse, faulty relay where used, open in the power supply circuit)
• Ground circuit issue at the Audio/Video Module “B” (loose ground point, corrosion, broken ground conductor, excessive voltage drop under load)
• Connector contamination or physical damage affecting network or power/ground terminals (moisture intrusion, corrosion, bent pins)
• Network backbone/junction or splice fault affecting the Audio/Video Module “B” branch (damaged splice, poor crimp, harness damage)
• Another module on the same network segment disrupting communications (network wiring fault elsewhere that loads the bus)
• Audio/Video Module “B” internal fault or software issue (consider only after verifying network integrity and stable power/ground)

Diagnosis Steps

Tools that help include a scan tool capable of full-network scans and viewing module status, a digital multimeter for power/ground and voltage-drop checks, and back-probing supplies. A wiring diagram and connector views are essential because the network type, splice locations, and module power/ground distribution vary by vehicle. If available, use a breakout lead or test harness to reduce terminal damage during testing.

1. Confirm the DTC and context. Perform a complete network scan and record all stored and pending codes across all modules, along with freeze-frame or event data where available. Note whether U018A is current/active or history, and whether other communication or power-related DTCs are present.
2. Verify the complaint and identify what is missing. Check whether the Audio/Video Module “B” is listed as “offline/not responding” in the scan tool topology. Attempt to enter the module directly; record whether the scan tool can communicate intermittently, consistently, or not at all.
3. Check for pattern clues. If multiple modules on the same network segment are offline, prioritize diagnosing the shared network backbone/junction/splice or a common power supply. If only the Audio/Video Module “B” is offline, focus on its specific power, ground, and branch network circuits.
4. Perform a visual inspection before testing. With the ignition off, inspect accessible harness routing and connectors for the Audio/Video Module “B” and nearby junctions/splices (location varies by vehicle). Look for chafing, pinch points, prior repair work, partially seated connectors, terminal damage, and contamination. Do not force connectors; use correct release methods.
5. Verify module power and ground integrity under load. Using wiring diagrams, identify all power feeds and grounds for the Audio/Video Module “B.” With the circuit energized as required by service info, check for proper power supply presence and perform voltage-drop testing on grounds and power feeds while the circuit is loaded. Excessive drop indicates resistance in wiring, connectors, fuses, or ground points.
6. Check fuses/relays correctly. If a fuse is associated with the Audio/Video Module “B,” confirm it is not only intact but also has proper feed on both sides in the operating mode that powers the module. If a relay is used, verify command and output operation per service information. Replace components only after identifying why a fuse opened or why a relay output is missing.
7. Evaluate the network branch to the module. With the module connector accessible and the correct key-off/key-on state per service information, test the network circuits for opens/shorts between the module connector and the next splice/junction/backbone point. Use continuity and short-to-power/short-to-ground checks as appropriate, and compare results side-to-side where the diagram shows paired lines.
8. Inspect terminals and perform a pin-fit check. Disconnect the Audio/Video Module “B” connector(s) and inspect terminals for spread pins, push-out, corrosion, or overheating. Perform a gentle retention/pin-fit check with the correct terminal tool or a known-good mating pin gauge method as specified by service information. Repair or replace terminals as needed.
9. Wiggle test for intermittents. Reconnect as needed, then monitor network/module status on the scan tool while gently manipulating the harness, connector body, and nearby splice areas. If communication drops in/out with movement, isolate the exact section and inspect for broken conductors, poor crimps, or terminal fretting.
10. Log live data/network status during the failure. If the issue is intermittent, drive or operate the vehicle in the conditions that reproduce the fault while logging the network scan status and relevant module wake/sleep or voltage PID information (as available). Use the timestamp of the communication loss to narrow the diagnostic focus to power/ground transitions, connector movement, or specific operating modes.
11. Rule out module fault last. If power, ground, and network wiring tests are all normal and the network segment is stable, consider the Audio/Video Module “B” as a suspect. Follow service information for any reset/relearn, configuration, or programming requirements. If substitution is used, ensure correct setup; do not condemn the module solely because it is offline without verifying its feeds and network circuits.

Professional tip: Treat “lost communication” as a network-and-power integrity problem first. A module that appears “dead” on the scan tool can be caused by a voltage-drop ground issue, a shared splice fault, or a connector terminal that opens only with vibration. Confirm stable power/ground under load and isolate the network branch with targeted tests before considering module replacement.

Possible Fixes & Repair Costs

Repair cost for U018A varies widely because the fix depends on why communication with the Audio/Video Module “B” was lost. Total effort is driven by diagnostic time, harness access, connector condition, and whether any module programming or configuration is required after repairs.

• Repair power/ground faults: Restore the module’s power feed(s) and ground(s) by repairing opens/high resistance, replacing damaged terminals, and correcting poor ground attachment points after confirming with testing.
• Network wiring repair: Repair CAN (or applicable network) bus opens/shorts, chafed insulation, pinched sections, or incorrect splices; confirm integrity with continuity checks (with power off) and voltage-drop testing under load.
• Connector/terminal service: Clean and tighten connectors, correct backed-out pins, replace spread/corroded terminals, and ensure proper connector seating/CPA engagement where used.
• Address intermittent wiring: Re-route and secure harnesses that are tensioned or rubbing; verify the fix with a controlled wiggle test and a road-test while logging communication status.
• Module reset/relearn: Perform a battery reset procedure only when appropriate for the platform, then re-check for U018A; follow service information for any required network/module reinitialization steps.
• Software update/configuration: If service information supports it, update or reconfigure modules involved in network communication; confirm that configuration matches the vehicle’s as-built options.
• Replace Audio/Video Module “B” (verified): Replace the module only after confirming proper power, ground, and network circuits at the module connector and ruling out wiring/connector faults; perform required setup/programming per service information.

Can I Still Drive With U018A?

Usually, yes, because U018A is a network communication fault tied to the audio/video system, so primary drivability may be unaffected; however, features controlled by or routed through the Audio/Video Module “B” may be inoperative or unstable. Do not drive if the vehicle also shows warnings related to braking, steering, reduced power, stalling, or a no-start condition, or if multiple network codes appear at once—those conditions suggest a broader network or power issue that can affect safety-critical systems.

What Happens If You Ignore U018A?

Ignoring U018A can leave audio/video functions unavailable and may cause repeated warning messages, intermittent display behavior, or accessory features not responding. If the underlying cause is a progressing wiring/connector problem or unstable module power/ground, the fault can spread to additional network communication codes and create harder-to-diagnose intermittents over time.

Last updated: March 17, 2026

Vehicles Commonly Affected by U018A

• Vehicles with multiple infotainment-related modules: Systems that separate display, tuner, amplifier, and video processing across different controllers.
• Vehicles with distributed network gateways: Platforms where infotainment modules communicate through a gateway between multiple networks.
• Vehicles with rear-seat entertainment or auxiliary video interfaces: Additional video modules increase network nodes and connectors.
• Vehicles with premium audio/video feature sets: More data traffic and more module interdependencies can expose marginal connections.
• Vehicles with recent electrical repairs: Harness disturbance, connector not fully seated, or pin fit issues after service work.
• Vehicles with known harness flex points: Areas where the harness moves with panels, seats, or hinges (varies by vehicle design).
• Vehicles operated in corrosive environments: Terminal corrosion and ground degradation can destabilize module power and communication.
• Vehicles with battery or charging concerns: Low or unstable system voltage can cause modules to drop off the network intermittently.

After any repair, confirm the fix by clearing codes, cycling the ignition as required, and verifying that communication with Audio/Video Module “B” remains stable during a road-test while monitoring network-related data and checking that U018A does not reset.