U0142 – Lost communication with body control module (BCM) B

Last updated: April 3, 2026

U0142 means your vehicle lost communication with Body Control Module (BCM) “B,” so features like locks, lights, windows, wipers, or the security system may act up or stop working. You may also see multiple warning messages because several modules rely on BCM data. According to manufacturer factory diagnostic data, this U0142 code indicates the network cannot receive valid messages from BCM B for a calibrated time. The code does not prove the BCM failed. It only proves other modules cannot “see” it on the network. Diagnosis must confirm power, ground, and network integrity first.

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U0142 Quick Answer

U0142 points to a network communication loss with BCM B. Check BCM B fuses, powers, grounds, and the network wiring/connectors before condemning any module.

What Does U0142 Mean?

U0142 meaning: one or more modules on the vehicle network set a fault because they cannot communicate with Body Control Module (BCM) B. In plain terms, the vehicle loses access to BCM-controlled functions and BCM-shared data. That can disable body features and trigger many “secondary” codes in other modules.

Technically, the reporting module monitors network message traffic and expects periodic messages from BCM B. When those messages stop or become invalid, it logs U0142 as a communication loss. The module does not measure BCM internal health. It only confirms that message exchange failed, which is why you must prove power/ground and network integrity before any BCM replacement.

Theory of Operation

Modern vehicles use a shared network (often CAN, sometimes multiple buses with a gateway) to move data between modules. The BCM manages many body loads and also publishes status messages. Other modules use those messages for logic, warnings, and authorization. BCM data can include key status, door ajar state, theft deterrent status, and lighting requests.

U0142 sets when BCM B stops communicating on its assigned network path. A module can “disappear” from a scan tool list when it loses power, loses ground, or drops off the bus. Network faults can do the same thing. An open, short, corrosion, water intrusion, or a backed-out terminal can distort bus signals and block messages. The “B” designator is manufacturer-defined, so you must confirm which physical BCM or network address the vehicle calls BCM B.

Symptoms

U0142 symptoms usually show up as body feature failures and a scan tool that cannot talk to BCM B.

• Scan tool: BCM B does not respond, disappears from the module list, or drops out during a network scan.
• Power locks: locks cycle incorrectly, do not respond, or work only from one switch.
• Exterior lighting: headlamps, park lamps, or turn signals act erratic or fail to operate.
• Interior functions: windows, wipers, HVAC request signals, or interior lamps work intermittently.
• Warning messages: multiple cluster warnings appear at once due to missing BCM data.
• Security/immobilizer: key recognition or theft deterrent functions act up, including no-start on some platforms.

Common Causes

• BCM B power feed fault (fuse, relay, splice, or open): When BCM B loses its primary B+ or ignition feed, it stops transmitting network messages and other modules log U0142.
• High-resistance BCM B ground (loose fastener, corrosion, paint under eyelet): A weak ground can let the BCM boot inconsistently and drop off the network under load, creating an intermittent or hard communication loss.
• Network harness damage near the BCM B location: Pinched, rubbed-through, or stretched wiring can open the communication pair or short it, which prevents valid message traffic to and from BCM B.
• Connector problems at BCM B (backed-out pins, water intrusion, terminal tension loss): Poor terminal contact raises resistance and causes the CAN/LIN signals or power/ground to fail when vibration or temperature changes occur.
• Short to ground or short to voltage on the communication circuit: A shorted network line forces the bus dominant or recessive, so modules cannot arbitrate messages and they flag a “lost communication” DTC.
• Open circuit in the communication circuit (CAN H/CAN L or LIN depending on vehicle): An open prevents the bias and differential signaling from forming correctly, so BCM B appears offline during a network scan.
• Another module or accessory pulling the network down: A failing module, aftermarket remote start, alarm, radio, or tracker can corrupt or load the bus and make BCM B look “missing.”
• BCM B internal fault (rare after circuit verification): Internal processor resets, failed transceiver, or water-damaged circuit boards can stop communication even when power, ground, and network integrity test good.

Diagnosis Steps

Use a scan tool that can run a full network scan and display module status. Keep a digital multimeter handy for voltage-drop tests and bus checks. Get the correct wiring diagram for the vehicle. A test light or headlamp bulb helps load circuits. Back-probe pins and terminal test tools prevent connector damage.

1. Confirm U0142 as stored, pending, or history, and record freeze-frame data. For U0142, focus on ignition state, vehicle speed, battery voltage, and any companion U-codes that identify which modules also lost messages.
2. Run a complete network scan and note whether BCM B appears and responds. If BCM B does not appear, treat it as an offline module. If it appears but logs U0142, suspect an intermittent drop-out or a bus disturbance.
3. Check for related codes first, especially low-voltage, battery disconnect, or other “lost communication” DTCs. Multiple modules reporting losses often points to a bus-wide problem or a power feed issue.
4. Check BCM B fuses and power distribution before probing the module. Verify each related fuse has power on both sides with the circuit energized, not just continuity.
5. Verify BCM B power and ground under load with voltage-drop testing. Load the circuit with the module connected and operating. Measure ground drop from BCM ground pin to battery negative and keep it under 0.1V. Then measure power-side drop from battery positive to the BCM B+ pin while the BCM is powered.
6. Inspect BCM B connectors and the surrounding harness. Look for water tracks, green corrosion, overheated terminals, and backed-out pins. Perform a light tug test on suspect wires and check terminal tension with the correct gauge tool.
7. Check the communication circuit at the BCM connector with ignition ON. Communication bias voltage only exists with the network powered, so ignition-off readings do not help. Compare CAN/LIN circuit behavior to service information and to a known-good section of the same network when possible.
8. Isolate the fault if the bus looks compromised. Disconnect BCM B and see if other modules return to normal communication. If the bus recovers, suspect BCM B or its connector/wiring. If the bus remains down, unplug other modules on that segment one at a time to find the node pulling the network offline.
9. Perform targeted continuity and short checks only after you confirm power and ground integrity. With the battery disconnected and modules unplugged as required by service info, check for opens between BCM B and the network splice, and check for shorts between communication lines and power/ground.
10. Use a scan tool snapshot during a road test if the concern is intermittent. Freeze frame shows conditions when U0142 set. A snapshot captures live module status, bus errors, and voltage during the exact moment the drop-out occurs.
11. After repairs, clear codes and rerun a full network scan. Confirm BCM B stays online through several key cycles and a vibration/temperature check. Recheck for pending vs confirmed behavior since some monitors need two trips to confirm, while hard communication faults often return immediately.

Professional tip: Do not condemn BCM B until you prove its power and grounds with voltage-drop under load. A corroded ground can show “12V present” with a meter, yet the BCM resets the moment it tries to drive network traffic. Also, if the network wakes up when you unplug BCM B, verify the connector for spread terminals before you call the module bad.

Possible Fixes

• Restore BCM B power feed or ignition feed by repairing the open, replacing the failed fuse/relay, or correcting a damaged splice.
• Clean, tighten, and rework BCM B grounds, then confirm less than 0.1V ground drop with the BCM operating.
• Repair harness damage or shorts in the communication wiring and secure the loom to prevent repeat rub-through.
• Clean and dry BCM B connectors, correct terminal tension, and replace damaged terminals or seals as needed.
• Remove or rewire aftermarket accessories that load or corrupt the network, then confirm bus stability on a full network scan.
• Reprogram or replace BCM B only after power, ground, connector, and network circuit tests prove the module cannot communicate.

Can I Still Drive With U0142?

You can often drive with a U0142 code, but expect body-related features to act up or quit. The vehicle may start and run normally. Still, treat it as a reliability and safety concern. The BCM controls or coordinates functions like exterior lighting, wipers, power locks, windows, keyless entry, immobilizer handshakes, and warning chimes. If those systems behave unpredictably, stop driving and diagnose it. Avoid night driving if lights, cluster warnings, or wipers show faults. If the vehicle shows a no-start, stuck in gear, or security indicator, do not keep cycling the key. Diagnose the network and BCM power feeds first.

How Serious Is This Code?

U0142 ranges from an inconvenience to a serious usability problem, depending on what BCM “B” supports on your platform. Some vehicles split BCM functions into two modules. Others label “BCM B” as a secondary body controller for specific loads. When the loss affects door locks, windows, or interior lights, the impact stays mostly comfort-related. The risk increases when the fault affects exterior lighting, wipers, instrument cluster messaging, or the immobilizer pathway. A network dropout can also trigger multiple warning lights and erratic accessory operation. If U0142 appears with many U-codes, suspect a network fault or power issue. Fix it soon to prevent intermittent no-starts and repeated battery drain.

Common Misdiagnoses

Parts get replaced because the symptoms look like a bad module. Techs often condemn BCM B when the real failure sits in power, ground, or the network splice. Another common miss involves a single blown fuse feeding the BCM wake-up circuit. The module then “disappears” on the scan. Many also skip a voltage-drop test under load. They check for 12 volts with no load and call it good. Corrosion in a ground eyelet can pass a static check but fail during wake-up. Shops also chase symptom codes first, like door lock actuator faults, and ignore the root U0142. Start with a full network scan and verify whether the scan tool can talk to BCM B.

Most Likely Fix

The most common confirmed repair path starts with restoring BCM B power and ground integrity. That includes correcting a blown fuse, a loose battery feed, or a high-resistance ground found with a loaded voltage-drop test. Next on the list sits connector and harness repair at the BCM location. Look for water intrusion, pin drag, and corrosion. If the scan tool never sees BCM B, and powers and grounds test good under load, then check the CAN/LIN communication circuits for opens or shorts. Only after those checks should you consider BCM B internal failure or a programming issue. Many BCM replacements require setup, variant coding, or immobilizer procedures.

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.