U0140
Lost Communication With Body Control Module
Encountering the engine check light code U0140 signifies an explicit mechanical or electrical operational breakdown categorized as "Lost Communication With Body Control Module". Professional scanner tools usually flag this subsystem loop early on.
Driver's Summary
Storing code U0140 is your car's way of telling you something is wrong with the lost communication with body control module. The most common signs are power windows/locks fail, radio dies, wipers won't work, erratic electrical behavior. Short trips are generally acceptable, but avoid high-load driving and get this inspected soon.
Symptoms
Power windows/locks fail, radio dies, wipers won't work, erratic electrical behavior
Common Causes
- Water leak damaging BCM (often under windshield/dashboard)
- Blown BCM fuse
- Corroded ground wire
- Failed BCM
How to Fix
- 1 Find and fix water leaks
- 2 Replace BCM power fuse
- 3 Clean BCM grounds
- 4 Replace and program Body Control Module
Technical Explanation
U0140 is stored after the control module confirms the fault over multiple ignition cycles, ruling out transient electrical noise as the cause. The affected module's power supply circuit (fuse, relay, and ground) is the first area the PCM checks via its own power monitoring circuits before flagging the loss of communication as a module fault rather than a network fault. Once confirmed, the code is stored as a permanent DTC and the MIL is activated. The freeze frame snapshot — recording RPM, load, coolant temperature, and fuel trim at fault detection — is also saved and is critical for accurate diagnosis.
Is It Safe to Drive?
Code U0140 allows for cautious short-distance driving, but the underlying cause — most likely water leak damaging bcm (often under windshield/dashboard) — will worsen with time. Fuel economy suffers, and ignoring the fault for weeks can turn a $50 fix into a much larger repair bill.
Mechanic's Pro Tip
When diagnosing U0140, start with the cheapest and most accessible potential causes first: verify fuses, relay operation, and connector integrity before purchasing any parts. Use a scan tool to capture live data during the fault condition — static readings with the fault absent often yield no useful information. Document the freeze frame data stored with the code; it records the exact engine conditions (RPM, load, coolant temp, fuel trim) at the moment the fault was detected and is invaluable for replicating the fault on a test drive.
Diagnostics/Leak repair: $100 - $300; BCM replacement: $300 - $800