U0140 – Lost Communication With Body Control Module

U0140 means your vehicle lost communication with the Body Control Module (BCM), so several comfort and convenience features may act up at once. You may see strange electrical behavior, warning messages, or a no-start depending on how the vehicle routes security and start authorization. According to manufacturer factory diagnostic data, this code indicates the network cannot exchange valid messages with the BCM for a set period. The BCM might still be fine. This DTC points first to a network, power, or ground problem that prevents the BCM from talking on the vehicle’s communication bus.

U0140 Quick Answer

U0140 points to a BCM communication dropout, not an automatic BCM failure. Start by confirming the BCM appears on the scan tool network list, then verify BCM power/grounds and the network wiring at the BCM connectors.

What Does U0140 Mean?

U0140’s official meaning is “Lost Communication With Body Control Module.” In plain terms, another module tried to talk to the BCM and could not. Because the BCM manages many body functions, the vehicle can lose power door locks, interior lighting logic, keyless entry, wipers, or even starting functions on some platforms. The exact feature set varies by make, model, and year. SAE intentionally keeps U-code descriptions general, so you must confirm which module logged U0140 and what symptoms match.

Technically, the reporting module monitors network message activity and expects valid BCM data on the vehicle communication network (often CAN, sometimes with gateway routing). When messages stop, look for an electrical reason first. A dead BCM, a blown BCM fuse, a bad ground, high resistance in a connector, or a network short can all create the same “lost communication” result. Diagnosis must prove whether the BCM lacks power, cannot transmit, or the bus cannot carry the signal.

Theory of Operation

Under normal operation, the BCM powers up with ignition or wake-up events and joins the vehicle network. It sends and receives messages for body functions and acts as a decision maker for outputs. Many cars also use the BCM as a network gateway, routing data between CAN segments or between CAN and LIN sub-networks. Other modules depend on BCM messages for state-of-vehicle data, like key status, door ajar status, and wake/sleep commands.

U0140 sets when those expected BCM messages disappear or become invalid. Loss of BCM power or ground stops communication instantly. A shorted CAN wire, corrosion at the BCM connector, or a pin fit issue can distort the bus and silence the BCM. A network fault can also take down multiple modules at once, which helps you separate “BCM offline” from “bus down.” Your job is to confirm whether the BCM is missing from the network scan, present but unstable, or present while another module falsely reports loss.

Symptoms

U0140 symptoms usually show up as multiple body electrical issues at the same time.

• Scan tool: BCM not responding, missing from the module list, intermittent scan tool dropout, or multiple U-codes stored across several modules
• Warning message: security/immobilizer message, key not detected, or “service” warnings that appear with no obvious single system failure
• No start or no crank: common on platforms where the BCM participates in start authorization or ignition mode management
• Interior functions: dome lamps, instrument illumination, or retained accessory power works intermittently or not at all
• Locks and keyless: power locks, remote keyless entry, or alarm functions become inoperative or erratic
• Wipers/windows: wiper logic, power windows, or washer functions act abnormal, especially after a battery event
• Battery drain: vehicle will not go to sleep because wake-up messages or network traffic stay active

Common Causes

• BCM power feed fault (fuse, relay, or splice): The BCM drops offline when it loses a key-on or battery feed, so other modules log U0140.
• BCM ground high resistance: Corrosion or a loose ground eyelet can pass a continuity test but fail under load, which resets the BCM and kills network messaging.
• CAN bus open on CAN-H or CAN-L near the BCM: An open circuit interrupts message traffic, so modules time out and set a lost communication code.
• CAN bus short to power or short to ground: A shorted data line holds the bus in a dominant or biased state, which blocks normal communication with the BCM.
• Connector fretting or water intrusion at the BCM: Terminal tension loss or moisture creates intermittent resistance, which causes sporadic module dropouts and U0140.
• Harness damage in common BCM locations: Pinched wiring at the kick panel, under-dash brackets, or door-sill routing can open or short the network or power feeds.
• Another module pulling the network down: A different controller with an internal fault can corrupt the bus, making the BCM appear “lost” even when it has power.
• Incorrect module configuration or recent programming event: A mismatched build configuration or incomplete setup can prevent normal network participation and trigger U0140.
• Body Control Module internal fault (rare): An internal failure can stop BCM message transmission, but you must prove power, ground, and bus integrity first.

Diagnosis Steps

Use a scan tool that can run a full network scan and display module status. Keep a digital multimeter available for voltage-drop testing under load. Pull the correct wiring diagrams for BCM power, grounds, and CAN circuits. A backprobe kit, terminal test leads, and basic harness repair tools prevent connector damage during checks.

1. Confirm U0140 as stored, pending, or history, then record freeze frame data. For communication faults, focus on ignition state, battery voltage, vehicle speed, and any companion U-codes or low-voltage codes captured at the same moment.
2. Run a complete network scan and note whether the BCM appears in the module list. If the scan tool cannot communicate with the BCM, treat this as a hard offline event until proven otherwise.
3. Check battery health and system voltage on the scan tool and at the battery posts. Low voltage during crank or jump-start events commonly triggers network dropouts that look like module faults.
4. Check BCM-related fuses, relays, and power distribution before you probe the BCM connector. Verify power on both sides of each fuse with the circuit powered, not just with a fuse removed.
5. Verify BCM power and ground under load with voltage-drop tests. Load the circuit by commanding BCM outputs on (if possible) or by turning on high current loads, then measure ground drop to the battery negative and keep it under 0.1V.
6. Inspect the BCM connectors and nearby harness routing. Look for water tracks, green corrosion, overheated pins, loose terminal fit, and evidence of prior repairs under the dash or in kick panels.
7. If the BCM stays offline, check CAN integrity at the BCM connector using the wiring diagram. Measure communication line voltages with ignition ON because bus bias voltage only exists when the network is powered.
8. Isolate the fault if the bus looks abnormal by disconnecting modules on the same network branch one at a time. Recheck network scan results after each isolation step to find a module or segment that drags the bus down.
9. When U0140 acts intermittent, use a scan tool snapshot during a road test or a harness wiggle test. Freeze frame shows conditions when the code set, while a snapshot captures live data at the instant the dropout occurs.
10. After repairs, clear codes and repeat the network scan, then complete a key-cycle and short drive. Confirm U0140 does not return as pending or confirmed, and confirm all BCM-dependent functions operate normally.

Professional tip: If multiple modules show “lost communication with BCM,” do not start by replacing the BCM. Prove BCM power, BCM grounds, and bus health first. A single high-resistance ground or a shorted network splice can mimic a failed module and waste hours.

Possible Fixes

• Repair BCM power feed issues such as blown fuses, loose fuse terminals, faulty relays, or damaged splices.
• Clean, tighten, and protect BCM ground connections, then verify ground voltage drop stays below 0.1V with the circuit loaded.
• Repair CAN wiring faults, including opens, shorts, and damaged twisted pair routing near the BCM or network junctions.
• Clean and correct BCM connector issues, including water intrusion, terminal tension loss, or backed-out pins.
• Identify and repair another module or branch circuit that pulls the network down, then confirm the BCM returns to the network scan.
• Perform required setup, configuration, or programming after verified electrical repairs when the vehicle requires it for network participation.

Can I Still Drive With U0140?

You can often drive with a U0140 code, but you should treat it as a reliability and safety risk. The Body Control Module (BCM) coordinates many “non-engine” functions that still affect control and visibility. Expect issues like inoperative gauges, warning chimes, interior lighting, wipers, power locks, HVAC commands, or a no-start on some platforms. If the vehicle shows a no-crank, intermittent stalling, loss of exterior lighting, or erratic security/immobilizer behavior, stop driving and diagnose it. Communication faults can escalate fast when vibration or moisture changes the circuit. Drive only as needed until you verify power, ground, and network integrity.

How Serious Is This Code?

U0140 ranges from an inconvenience to a “tow it in” problem, depending on what your BCM controls. When the BCM only supports comfort features, you may only lose power windows, locks, or interior lights. Severity increases when the BCM participates in immobilizer logic, exterior lighting commands, wiper control, or gateway routing for other modules. In those cases, you can face a no-start, a dead cluster, or multiple modules dropping off the network. Treat any headlight, brake light, wiper, or security-related malfunction as a safety issue. If your scan shows many U-codes across modules, suspect a network or power distribution fault, not a single failed module.

Common Misdiagnoses

Technicians waste money on BCM replacement because U0140 “names” the BCM. The code only says other modules lost messages from it. A blown BCM fuse, a corroded ground, or a loose connector can create the same symptom. Another common miss involves checking voltage with no load. A corroded splice may show 12 volts open-circuit, then collapse under load and reboot the BCM. Many also skip a full network scan. A shorted module elsewhere can pull the bus down and make the BCM look dead. Avoid guesswork: verify module presence on the scan tool, confirm BCM power and grounds with voltage-drop tests, then evaluate bus integrity.

Most Likely Fix

The most common confirmed U0140 repair path starts with restoring BCM power or ground integrity. That includes replacing a blown fuse, repairing a loose fuse box terminal, or fixing a corroded ground point with a proven voltage-drop failure under load. The next frequent fix involves connector or harness repair at the BCM or at a nearby junction block, especially after water intrusion or prior body work. If the scan tool cannot communicate with the BCM after you prove clean powers, grounds, and stable network circuits, then module replacement and configuration become the next step. Programming requirements vary by manufacturer, so confirm with service information before ordering parts.

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 1, 2026