May not start if BCM holds immobiliser. Electrics inoperative. U0140 means the ECM or another module has lost communication with the Body Control Module (BCM) on the CAN network — the BCM is not transmitting its expected data frames.
What U0140 means
The Body Control Module is the central hub for most electrical comfort and convenience features — door locks, windows, interior lighting, exterior lighting, HVAC blower control, horn, and security system. Beyond convenience, the BCM also communicates critical data to the powertrain and chassis modules: many BCMs broadcast battery state-of-charge, ignition switch status, and door/hood/trunk switch states that other modules need for their own logic. U0140 is stored when the ECM or another module stops receiving the BCM's expected CAN bus transmissions. Since the BCM is often powered directly from the battery and not through the ignition relay, U0140 can occur even with the ignition on if the BCM's main fuse has blown or its connector is damaged.
Symptoms
- Multiple electrical features suddenly non-functional — power windows, locks, interior lights, or horn may all stop working simultaneously
- Check engine light on alongside multiple body/electrical warning messages
- Security system may activate erroneously or the vehicle may not start if the BCM handles the immobiliser function
- HVAC system defaulting to maximum blower or refusing to respond to controls if the BCM governs blower motor relay
- Instrument cluster may display multiple warning messages or lose gauge function
Common causes
- Corroded or damaged BCM connector — moisture entering a BCM connector destroys pin contacts and is the most common U0140 cause
- Failed BCM due to water damage — modules mounted under the dashboard or in the footwell are vulnerable to flooding from windshield seal leaks
- Blown BCM fuse or failed BCM power relay — without power, the BCM cannot transmit on the CAN bus
- CAN bus wiring fault between the BCM and the network junction — a chafed or broken CAN High or CAN Low wire isolates the BCM from the network
- Battery voltage too low to sustain BCM operation — modules typically need at least 9–10V to communicate reliably
Severity & driving advice
Severity: High — Loss of BCM communication disables body electrical systems and may prevent starting if the BCM controls the immobiliser. Diagnose promptly.
Can I drive? May not start if BCM holds immobiliser. Electrics inoperative.
Diagnostic approach
- Confirm which module is offline using a full-system scan — Use a professional scan tool capable of querying all modules. U0140 should be stored in the ECM and any other modules that depend on BCM data. If the scan tool shows the BCM is not visible or not responding to module-specific queries, the BCM is confirmed offline. Note: some scan tools show the BCM as present but with no live data — this also indicates a communication fault.
- Check BCM fuses and power supply — Locate all fuses supplying the BCM — there are typically two or three, including a main feed and a memory keep-alive supply (the latter keeps settings in memory with the key off). Check each fuse with a test light or multimeter (not just visual inspection). Verify battery voltage is present at the BCM's power supply pins with the fuses confirmed good.
- Inspect the BCM connector and mounting location for water damage — The BCM is commonly mounted under the dashboard (driver's side knee panel) or in the centre console area. Check for water staining on the carpet or foam insulation near the module. Unplug the connector and inspect both the module's pins and the harness-side connector for corrosion, greenish oxide on contacts, or water residue. Water damage to the BCM itself often requires replacement — corrosion on pins can sometimes be cleaned and treated with dielectric grease.
- Test CAN bus resistance at the OBD-II port and at the BCM — With all modules powered off (key out, battery briefly disconnected then reconnected), measure resistance between CAN High (pin 6) and CAN Low (pin 14) at the OBD-II port — it should read approximately 60 Ω if both termination resistors are intact. If resistance is higher (above 120 Ω), one terminator or the BCM's CAN transceiver may be open. Trace CAN H and CAN L wires from the BCM connector to the CAN junction for continuity and shorts.
Make & model notes
Chrysler / Dodge / Jeep (Stellantis): 2007–2013 Jeep Wrangler, Liberty, and Dodge vehicles have a well-known U0140 vulnerability from water intrusion into the BCM connector under the dashboard. The BCM is mounted low in the passenger footwell area on some models — carpet soaking from a leaking heater core or windshield seal carries water directly to the connector.
General Motors: GM's 2003–2009 full-size trucks and SUVs (Silverado, Tahoe, Suburban, Yukon) develop U0140 from BCM programming corruption after battery drain events or jump-starting incidents. A BCM that has lost its calibration may need to be reprogrammed rather than replaced.
Ford: Ford Focus, Fusion, and Explorer BCMs can lose communication after battery drain. A 'BCM relearn' or parameter reset via Ford's IDS/FDRS scan tool is sometimes sufficient to restore function without replacing the module.
FAQ
Will U0140 stop my car from starting?
On vehicles where the BCM controls the immobiliser or starter relay, yes — U0140 can cause a no-start. The security system may arm itself and not recognise the key because the BCM cannot process the transponder signal. This is why BCM communication faults should be diagnosed urgently even if the rest of the vehicle seems functional.
Can I replace the BCM myself?
You can physically replace the BCM, but most BCMs require VIN-specific programming after installation to match the vehicle's other modules, immobiliser settings, and option configurations. A BCM that is not programmed will either not communicate or will trigger multiple fault codes. Plan for dealer or shop programming.
Why do so many different electrical features stop working when U0140 is stored?
The BCM is the gateway for most body electrical functions — it directly controls or relays signals for windows, locks, lights, HVAC, and security. When the BCM drops off the CAN bus, all modules that depend on its broadcasts stop receiving input and default to safe states. What appears to be multiple failures is often a single BCM fault causing a cascade.
U0140 cleared after I charged the battery — is the BCM okay?
A low battery is a common cause of intermittent U0140, and if the code does not return after a full charge and load test, the battery was likely the culprit. Monitor over the next few days. If U0140 returns even with a fully charged battery, the fault is in the BCM connector, wiring, or the module itself.