B150A – Lost communication with HMI-LAN (Toyota)

B150A means your 2015 Toyota Auris lost communication on the HMI-LAN, so the audio and display functions may act up or stop responding. You may see a blank screen, frozen controls, or missing menu features. According to Toyota factory diagnostic data, this is a manufacturer-specific body DTC that indicates “Lost communication with HMI-LAN.” This code does not prove a bad radio or screen. It tells you a network link failed long enough for a module to flag a communication loss. Diagnose the power, ground, and network wiring first. Confirm which module dropped off the network before replacing anything.

B150A Quick Answer

B150A on Toyota indicates a loss of communication on the HMI-LAN network. Fix it by confirming which HMI-related module stopped talking, then checking power, ground, and network integrity at that module.

What Does B150A Mean?

Official definition: “Lost communication with HMI-LAN.” In plain terms, a Toyota body-related module expected to “hear” another device on the Human Machine Interface network, but it did not. In real use, the car can lose infotainment, display, or control-panel functions. The vehicle may still drive normally, but the user interface can become unreliable.

What the module checks and why it matters: The module that set B150A monitors message traffic and network presence on the HMI-LAN. It looks for expected communication within a time window. When it misses messages, it stores the DTC to point you toward a network, power/ground, or module wake-up problem. That distinction matters because a simple voltage drop at a connector can mimic a failed HMI unit.

Theory of Operation

On Toyota platforms, HMI-related devices share data over a dedicated communication link that supports the display, audio, and user input functions. Each device wakes up, powers its internal logic, and then transmits network messages. Other modules use those messages to coordinate screen content, button commands, and system status.

B150A sets when a module stops receiving the expected HMI-LAN traffic. A wiring fault can block messages. A weak power or ground can reboot a module and make it disappear from the network. Sleep/wake control faults can also keep a device offline, even with good wiring.

Symptoms

B150A most often shows up as a network dropout that affects the Toyota infotainment and display interface.

• Scan tool HMI-related ECU missing from the ECU list, shows “no communication,” or drops out intermittently during a health check
• Display screen blank, frozen, rebooting, or stuck on a logo
• Controls buttons or touch input lag, no response, or wrong function selection
• Audio no sound output, source switching fails, or volume control behaves erratically
• Menus missing settings pages, disabled options, or repeated “system unavailable” messages
• Intermittent problem changes with bumps, temperature, or after aftermarket accessory use
• Battery history symptoms begin after a weak battery, jump start, or battery disconnect

Common Causes

• HMI-LAN open circuit: A break in the HMI-LAN wiring stops message traffic, so the Toyota body network reports a lost communication event.
• HMI-LAN short to ground or power: A rubbed-through harness can pull the network line low or high and block data exchange between modules.
• High resistance at a connector (pin fit, corrosion, fretting): Increased resistance distorts signal edges and causes intermittent dropouts that set communication loss codes.
• Loss of power or ground at an HMI-LAN node: A module that loses feed or ground drops off the network and other modules log lost communication.
• Incorrect back-probed test method or terminal damage from probing: Spreading terminals or piercing insulation creates new resistance or intermittent opens that mimic the original fault.
• Aftermarket accessory tie-in to audio/HMI wiring: Poorly integrated radios, alarms, or trackers can load the network or introduce shorts near HMI-related harnesses.
• Water intrusion at dash or kick panel harness junctions: Moisture wicks into splices and connectors and causes corrosion-driven intermittents, especially during temperature swings.
• Module reset due to unstable system voltage: Weak battery, charging issues, or poor main connections can reboot network nodes and trigger lost communication entries.
• Network gateway or related module internal fault: A failing node can stop transmitting or jam traffic, but you must prove wiring integrity first.

Diagnosis Steps

Use a scan tool that can run a full Toyota body network health check and show a network list. Have a quality digital multimeter for voltage-drop testing under load. Keep a back-probe kit and terminal tools ready. A wiring diagram for the Auris body network helps you identify the HMI-LAN splice points and shared power feeds.

1. Confirm DTC B150A and record all stored, pending, and history codes. Save freeze frame data if the tool provides it for body codes. Focus on ignition state, vehicle speed, system voltage, and any companion communication or low-voltage codes. Freeze frame shows conditions when the fault set, not what happens now.
2. Run a full network scan and verify which ECUs appear online. Note any modules that the scan tool shows as “not responding” or “no communication.” For communication codes, this step comes before meter work. If the suspected HMI-related node never appears, treat the concern as power/ground, connector, or network physical-layer first.
3. Check fuses and power distribution that feed the body network and the suspected HMI-LAN node. Do not rely on visual checks alone. Load-test the fuse circuit with the circuit active when possible. Also inspect battery terminals and main grounds because unstable voltage can reset network modules.
4. Verify ECU power and ground under load at the suspected HMI-LAN module or gateway. Perform voltage-drop testing, not continuity alone. With the module connected and operating, measure ground drop and keep it under 0.1V. Next, check voltage drop on the power feed under load to catch high-resistance joints.
5. Inspect connectors and harness routing at common stress points. Look at dash harness areas, kick panels, behind the radio/HMI stack, and any junction blocks used for body wiring. Check for water trails, green corrosion, pushed-back pins, and loose locking tabs. Stop and repair terminal issues before deeper testing.
6. Check for aftermarket device connections near the audio/HMI wiring. Remove non-OEM splices, Scotch-lock taps, and add-on harness adapters if present. Then retest for module presence on the scan tool network list. A quick isolation step often turns an intermittent into a repeatable pass or fail.
7. Perform communication line checks with ignition ON. Communication line bias and activity depend on powered modules, so ignition-off readings do not help. Use the wiring diagram to identify the HMI-LAN pair or line set. Measure for shorts to ground or power, and compare readings at the module connector versus an accessible junction to locate the fault section.
8. If the tool supports it, monitor network-related data and module status while you wiggle-test the harness. Target the exact harness runs you inspected earlier. Use a scan tool snapshot to capture live network status during the wiggle test. A snapshot differs from freeze frame because you trigger it during diagnosis to catch an intermittent dropout.
9. Isolate the fault by unplugging nodes one at a time only when service information supports it. Watch whether communication returns for other modules after a suspect node disconnects. This helps you identify a node that loads the network. Do not condemn a module until you prove power, ground, and line integrity to that connector.
10. Repair the verified issue and clear codes. Cycle the ignition and re-run the network scan to confirm all modules communicate. Road test under similar conditions to the freeze frame when possible. Confirm the DTC does not return as pending, history, or confirmed.

Professional tip: Treat B150A as a network integrity problem first, not a module replacement decision. A clean continuity check can still hide a bad ground or corroded splice. Voltage-drop tests under load and a scan tool network list usually pinpoint the real failure faster than swapping parts.

Possible Fixes

• Repair open/short in the HMI-LAN wiring: Restore damaged sections using proper splicing methods and route the harness to prevent repeat chafe.
• Clean and correct terminal fit at affected connectors: Remove corrosion, repair pin tension issues, and replace damaged terminals, then verify stable communication.
• Restore module power/ground integrity: Repair fuse feed issues, ground points, or high-resistance junctions confirmed by voltage-drop testing.
• Remove or correct aftermarket accessory wiring: Rewire accessories using proper power sources and isolation so they do not load or short HMI-related circuits.
• Repair water intrusion source and affected wiring: Fix leaks first, then repair corroded splices or connectors and recheck network stability.
• Replace a confirmed faulty network node only after testing: Replace the HMI-related module or gateway only after you prove good power, ground, and network lines at its connector.

Can I Still Drive With B150A?

You can usually drive a 2015 Toyota Auris with B150A, because this code reports a body-network communication loss, not an engine control fault. Expect the multimedia and display features to act up. The head unit, screen, steering wheel audio switches, Bluetooth, camera display, or vehicle setting menus may drop out. Drive with extra attention if you lost a rear camera image or warning chimes. Do not ignore the battery warning light or charging problems. Low system voltage can trigger network dropouts and create multiple false codes.

How Serious Is This Code?

B150A ranges from an inconvenience to a meaningful driver-information issue. When the HMI-LAN drops out, the vehicle often still starts and drives normally. Many owners only notice a dead screen or intermittent audio. Severity rises if the HMI provides critical prompts, camera display, or integrated warnings on your trim level. The bigger concern involves root cause. A weak battery, unstable charging, or a poor ground can disrupt multiple networks and modules. If you see several communication codes at once, treat it as a power or network integrity problem and diagnose it soon.

Common Misdiagnoses

Technicians often replace the radio, display, or amplifier because “the screen is dead.” That wastes money when the real fault sits in power, ground, or the LAN wiring. Another common miss involves skipping a network-wide scan. If other Toyota body modules show low-voltage or communication codes, B150A may only be a symptom. People also unplug connectors and create new faults, then blame the module. Confirm the scan tool can see each module, then load-test powers and grounds with voltage-drop checks. Finally, avoid condemning a module without checking for corrosion, water intrusion, or pin fit at the HMI-LAN connectors.

Most Likely Fix

The most common confirmed repair direction involves restoring stable power and ground to the HMI-related components, then repairing the communication path. Shops frequently fix a loose ground point, high resistance at a connector, or an accessory power feed issue that resets the HMI network. The next most common direction involves wiring repair at a stressed harness section or a connector with spread terminals near the head unit or dash junctions. Only consider module replacement after you prove correct power, ground, and network continuity, and after a recheck shows the module still drops off the network.

Repair Costs

Network and communication fault repairs vary by root cause — wiring/connectors are often the source, but module-level repairs or replacements can be significantly more expensive.

Last updated: April 3, 2026