U0142 – Lost Communication With Body Control Module “B”

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

Definition source: SAE J2012/J2012DA (industry standard)

U0142 indicates the vehicle network detected a loss of communication with Body Control Module “B” (BCM “B”). In practical terms, one or more other modules expected messages from BCM “B” over the data network and did not receive them for a calibrated period, so the network monitor flagged the fault. The exact warning indicators, affected features, and whether the issue is continuous or intermittent can vary by vehicle, network design, and module configuration. Always verify the module location, connector views, network topology, and any related diagnostic routines in the appropriate service information before testing or replacing parts.

What Does U0142 Mean?

U0142 – Lost Communication With Body Control Module “B” means that network communication with BCM “B” has been lost. Under SAE J2012 DTC conventions, “U” codes relate to network communications, and this entry specifically identifies a missing communications condition involving the designated body control module instance “B.” The code does not, by itself, prove the module is defective; it only indicates that expected network messages are not being received or acknowledged as required. The root cause must be confirmed through testing of the network wiring, connectors, power/ground to the module, and the module’s ability to communicate.

Quick Reference

• Subsystem: Network communications involving Body Control Module “B” (BCM “B”).
• Common triggers: Missing network messages from BCM “B,” intermittent network dropout, module reset, or loss of BCM “B” power/ground.
• Likely root-cause buckets: Wiring/connector faults, network line issues, BCM “B” power or ground problems, module internal fault, configuration/software (varies by vehicle).
• Severity: Varies; may cause multiple body-related features to stop working and may illuminate warning indicators; typically not engine-mechanical, but can affect safety-related functions depending on design.
• First checks: Scan for companion U-codes, verify battery/charging health, check BCM “B” fuses/feeds/grounds, and inspect connectors for looseness or corrosion.
• Common mistakes: Replacing BCM “B” without confirming power/ground integrity or network wiring condition; ignoring related codes that point to a broader network fault.

Theory of Operation

Modern vehicles use a shared data network so modules can exchange information and coordinate functions. BCM “B” is a node on that network and typically broadcasts and/or responds with data needed by other controllers. Each receiving module expects certain messages at regular intervals. If those messages stop arriving—due to an open or short in the network wiring, excessive resistance at a connector, a module that resets or loses power/ground, or a network disruption—the receiving module(s) will conclude that communication with BCM “B” has been lost and set U0142.

Depending on architecture, the fault may be set by multiple modules, or by a central gateway that supervises communications. Intermittent issues can occur when vibration, temperature change, or harness movement affects connection quality, briefly interrupting network signaling. Because communication faults can cascade, confirming whether BCM “B” is truly offline (and why) is the key diagnostic goal.

Symptoms

• Warning lights: One or more warning indicators illuminated, possibly including a general malfunction indicator depending on vehicle strategy.
• Body functions: Loss or erratic operation of body-related features that rely on BCM “B” (feature set varies by vehicle).
• Cluster messages: Information center warnings, “service” messages, or fault notifications related to communications.
• Intermittency: Symptoms that appear and disappear with bumps, steering movement, door operation, or temperature changes.
• Multiple codes: Additional network DTCs stored in other modules due to the same communication dropout.
• No communication: Scan tool may fail to communicate with BCM “B” while still connecting to other modules.

Common Causes

• Open circuit, short-to-power, or short-to-ground in the network communication lines between modules (varies by vehicle network design)
• High resistance or intermittent connection at the Body Control Module “B” connector(s) due to poor terminal fit, fretting, or pin damage
• Loss of power feed to Body Control Module “B” (blown fuse, faulty relay, open feed circuit, or excessive voltage drop under load)
• Loss of ground to Body Control Module “B” (loose ground fastener, corroded ground point, broken ground lead, or excessive voltage drop)
• Network splice/ junction connection fault (loose splice pack, damaged harness section, or water intrusion at a junction)
• Module offline due to improper wake/sleep behavior caused by a network issue, low system voltage condition, or a power/ground integrity problem
• Connector contamination or water intrusion in harness/connectors affecting network and/or module power/ground circuits
• Body Control Module “B” internal fault (hardware) or software issue, only after network and power/ground checks are proven good

Diagnosis Steps

Tools commonly needed include a scan tool capable of full-network scans, reading module status, and viewing freeze-frame or event data; a digital multimeter; wiring diagrams and connector views from service information; and basic backprobing tools. An oscilloscope is helpful where supported to observe network signal quality, but many faults can be isolated with network scan results plus power/ground and voltage-drop testing.

1. Confirm the complaint and perform a full network scan: Record all stored, pending, and history codes from every module. Note which modules report lost communication and whether Body Control Module “B” is listed as present/online or absent/offline.
2. Check for power supply or low-voltage related codes: If multiple modules show communication codes or low-voltage codes, address base power/charging and main power distribution concerns first; widespread network codes often follow system voltage instability.
3. Verify scan tool communication with Body Control Module “B”: Attempt to enter the module directly. If it communicates intermittently, capture session drops and note when they occur (key states, loads, bumps, harness movement).
4. Review module status and network topology (varies by vehicle): Using service information, identify which network(s) Body Control Module “B” is on, related gateways, and the physical locations of connectors, splice points, and grounds that can affect it.
5. Inspect fuses, relays, and wake feeds for the module: Check all fuses that supply Body Control Module “B,” including ignition and battery feeds. Don’t rely on visual checks alone; verify power is present at the fuse output and at the module feed circuits under the same key state that sets U0142.
6. Perform power and ground voltage-drop tests under load: With the module connected, measure voltage drop on each power feed and each ground path while the circuit is loaded (key on, commanded loads if applicable). Excessive drop indicates resistance in the feed/ground path even when static voltage looks acceptable.
7. Check connector condition and terminal integrity: Disconnect the module (as required by service procedures) and inspect for spread terminals, pushed-out pins, corrosion, moisture, or damaged seals. Perform a light terminal drag/tension check where permitted and verify proper connector locking.
8. Inspect network wiring, splices, and junctions: Trace the communication lines from Body Control Module “B” to nearby splice points/junction connectors. Look for harness chafing, pinch points, prior repair areas, and water paths. Repair any physical damage before deeper signal testing.
9. Wiggle test with live monitoring: Reconnect as needed and monitor network/module status on the scan tool while gently moving the harness, connectors, and suspected splice locations. Log data so you can correlate a dropout to a specific movement or area.
10. Isolate the fault if the module remains offline: If Body Control Module “B” will not communicate, follow service information to test the network segment for opens/shorts and to isolate by disconnecting branches/modules one at a time (where allowed). If network wiring and power/ground are proven good and the bus recovers only when the module is disconnected, suspect the module.
11. Verify the repair and prevent recurrence: After repairs, clear codes, run a complete network scan, and complete an ignition cycle road test while monitoring module presence and communication status. Recheck for returning U0142 and for any companion codes that might indicate an unresolved power/ground or network integrity issue.

Professional tip: Treat U0142 as a communication integrity problem first, not an immediate module replacement. The fastest way to avoid unnecessary parts is to prove module power and grounds with voltage-drop testing during the exact conditions that set the code, then use a full-network scan to determine whether the problem is localized to Body Control Module “B” or systemic across the network.

Possible Fixes & Repair Costs

Repair cost and effort vary widely because the same “lost communication” report can be caused by anything from a simple connection issue to a power/ground fault or a module that is offline. Confirm the root cause with testing before replacing parts.

• Repair wiring damage or high-resistance sections in the network communication circuits (as identified by continuity and voltage-drop testing).
• Clean, dry, and re-seat affected connectors; correct terminal pin-fit problems (spread, backed-out, corroded, or loose terminals).
• Restore module power and ground feeds (repair blown feed, poor ground, or excessive voltage drop in the supply/return path).
• Address related network faults that can pull the bus down (short-to-ground/short-to-power on the communication pair, if present).
• Update or reconfigure control-module software only if service information calls for it after verifying power/ground and network integrity.
• Replace the targeted module only after confirming correct power/ground, correct network circuits, and that the module still will not communicate.

Can I Still Drive With U0142?

Sometimes you can, but it depends on which functions are managed through Body Control Module “B” and how the vehicle is designed. If you have no-start, stalling, warning messages for braking/steering, inoperative exterior lighting, wipers, or other safety-related features, do not drive—have it diagnosed. If the vehicle drives normally, limit driving, avoid night/poor weather, and schedule testing soon because the fault can become intermittent and worsen without warning.

What Happens If You Ignore U0142?

Ignoring U0142 can lead to intermittent or permanent loss of body-related functions, recurring warning indicators, battery drain from modules not sleeping correctly, and unpredictable electrical behavior as communication drops in and out. If the underlying cause is a deteriorating connection or wiring damage, it may progress to additional network faults and wider system disruptions.

Last updated: March 16, 2026

Vehicles Commonly Affected by U0142

• Vehicles with multiple body control modules (a secondary or “B” body controller on the network)
• Vehicles using a high-speed and/or low-speed in-vehicle network for body functions
• Vehicles with extensive comfort and convenience features integrated through a body network
• Vehicles with multiple gateway modules bridging different communication buses
• Vehicles with recent collision repair, interior work, or electrical accessory installation (varies by vehicle)
• Vehicles operating in harsh environments that accelerate connector corrosion (humidity, road spray, temperature swings)
• Vehicles with known battery or charging-system issues that can affect module communication stability
• Vehicles with wiring harnesses routed through high-movement areas (doors, liftgate, under-seat areas), depending on design

For an accurate repair plan, treat U0142 as a network communication fault and confirm power, ground, and network circuit integrity before concluding any module is defective.