U0140 Code: Lost Communication With Body Control Module
Other modules stopped hearing from the body control module that runs lights, locks, wipers and more.
At a glance
Severity: Moderate
- Meaning
- Lost Communication With Body Control Module
- System
- Module Communication · Network
- Safe to drive?
- With caution
- Typical repair cost
- $10–$1,200
- DIY difficulty
- Moderate
U0140 is stored by the engine computer, instrument cluster or other modules when the body control module (BCM) stops sending its messages on the network. The BCM is usually mounted under the dash on the driver or passenger side, behind a kick panel or the glovebox, and controls interior and exterior lighting, power locks, wipers, horn, keyless entry and often the anti-theft system. When it goes silent, those functions act up or quit, the cluster may show warnings, and on vehicles where the BCM handles the immobilizer the engine may crank but not start. Water leaking into the footwell, a battery that went flat, a blown BCM fuse and poorly installed remote starters or alarms are the usual culprits.
Can I keep driving? If headlights, turn signals and wipers still work, you can drive carefully to a shop. If any of them are dead or behave randomly, don't drive at night or in rain until it's fixed.
How to read U0140
- U Network
- 0 Generic (SAE)
- 1 Module Communication
- 40 Specific fault
Symptoms
- Headlights, turn signals or interior lights not working or staying on
- Power locks, key fob or push-button start acting erratically
- Wipers running on their own or not at all
- Engine cranks but won't start, with a security light on
- Battery drains overnight because the module no longer goes to sleep
- Several unrelated warning messages on the instrument cluster
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Water in the footwell from a windshield, cowl, sunroof drain or A/C drain leak soaking the BCM or its connectors
- Blown fuse or weak power/ground to the BCM (it usually has several feeds)
- Low battery voltage, a jump start or a battery that went completely flat
- Aftermarket remote start, alarm or lighting wired into BCM circuits
- Internal BCM failure
- Damaged CAN wiring between the BCM and the network
Diagnosis step by step
Scan every module and note what else is missing
Record which modules set U0140 and whether other lost-communication codes are present. If only the BCM is missing, work at the BCM; if many modules are missing, the problem is on the shared network or its power supply.
Tools: OBD-II scanner
Feel the carpet and look for water
Pull back the footwell carpet under the BCM and check for dampness, water lines or a musty smell. Trace any water back to its source, such as a clogged cowl or sunroof drain, before replacing parts, or the new module will fail too.
Tools: Flashlight
Test all BCM fuses and grounds
The BCM typically has several battery and ignition feeds in the interior and underhood fuse boxes. Test each fuse with a meter, then voltage-drop test the BCM ground; more than about 0.1 V points to a corroded ground point.
Tools: Multimeter, Flashlight
Remove aftermarket devices
Look for remote starters, alarm modules and bypass modules spliced into the harness near the BCM. Disconnect them, clear codes and retest; poor splices on BCM wires cause many intermittent faults.
Tools: Screwdriver, Pliers
Check for a parasitic drain
With everything off and the car locked, the battery draw should fall to roughly 50 mA or less within about 30 to 45 minutes. A BCM that never goes to sleep keeps the current high and is a sign of an internal or wake-up fault.
Tools: Multimeter
Inspect BCM connectors and confirm the module
Unplug the BCM connectors and look for corrosion and pushed-out pins. If power, ground and CAN lines test good and the BCM still doesn't answer, replace it; most need programming and a key or immobilizer relearn.
Tools: Flashlight, Multimeter, OBD-II scanner
Where the parts are
- 1Battery
- 2Alternator
- 3Engine computer (ECM)
- 4CAN bus
- 5Transmission
- 6Wheel speed sensor
- 7High-voltage battery
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace BCM fuse / clean ground | Yes | $10–$120 |
| Fix water leak (drain, cowl or windshield seal) | No | $100–$600 |
| Remove or rewire aftermarket accessory | No | $80–$300 |
| Replace and program body control module | No | $400–$1,200 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Field data
| Ford | 7 | Escape, Explorer, F-150 REGULAR CAB | |
|---|---|---|---|
| Chevrolet | 5 | Avalanche, Cobalt, Cruze | |
| Jeep | 4 | Cherokee, Wrangler | |
| Mazda | 3 | Mazda3 |
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Depends
U0140 often does not turn on the check engine light, so it may pass the emissions part of a smog check. States with a safety inspection will fail the car if headlights, brake lights, turn signals, horn or wipers are affected.
Frequently asked questions
Why does U0140 make my car not start?
On many vehicles the BCM takes part in the immobilizer check or reports the key status to the engine computer. If that message is missing, the engine computer won't allow fueling or cranking even though the engine is fine.
Could a leak really kill the BCM?
Yes. The BCM usually sits low in a footwell, and water from a blocked drain or leaking seal collects right there. Corroded connectors and circuit boards are a common reason for BCM failures.
Can I swap in a used BCM from a junkyard?
Sometimes, but most BCMs are tied to the VIN and key data. A used one normally needs reprogramming or the original configuration and key data transferred.
Why is my battery going flat along with this code?
A BCM that keeps waking up or never goes to sleep can draw enough current to drain a battery overnight. Measuring sleep current tells you whether the BCM is the drain.
Sources
- SAE J2012 – Diagnostic Trouble Code Definitions
- ISO 15031-6 – Road vehicles, diagnostic trouble code definitions (EOBD)
- Manufacturer public service information (cross-checked)
- NHTSA Complaints API
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy