U0140
Lost Communication With Body Control ModuleU0140 is a generic OBD-II network diagnostic trouble code: Lost Communication With Body Control Module. It is logged by the engine control unit when the network monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What U0140 means
DTC U0140 is set when the Powertrain Control Module (PCM) or another control module on the vehicle's Controller Area Network (CAN) bus fails to receive expected messages from the Body Control Module (BCM) for longer than a manufacturer-defined threshold — typically around 250 milliseconds. The BCM is the central hub for a wide range of body electrical functions including power door locks, windows, exterior and interior lighting, wiper control, horn, and in many vehicles, inputs to the passive restraint and immobiliser systems. When CAN communication to it is interrupted, the initiating module logs U0140 and may disable features that depend on BCM data.
The most frequent root cause is not an outright module failure but rather a wiring or connector fault on the CAN bus itself — a chafed wire shorting to ground or battery voltage, a corroded connector pin, or a loose ground shared by the BCM. Because the CAN network is a two-wire differential bus, a single damaged wire can simultaneously affect several modules and produce multiple U01xx communication codes.
Diagnosis requires a scan tool capable of reading live CAN bus data to determine whether the BCM is transmitting at all.
Common causes
Most-frequently reported root causes when U0140 is logged.
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1
Damaged, chafed, or corroded CAN-bus High/Low wiring between PCM and BCM
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2
Loose or corroded BCM connector pins (CAN H/L circuits or power/ground pins)
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3
Open or short circuit on the CAN bus wiring harness
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4
Failed or internally shorted Body Control Module
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5
Poor BCM chassis ground or missing power supply fuse/relay
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6
Faulty PCM or other network node pulling the bus to a fault state
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7
Water intrusion into BCM or underdash connector causing intermittent short
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8
Aftermarket accessory (alarm, remote-start) incorrectly wired into the CAN bus
Symptoms drivers notice
How to diagnose U0140
A typical diagnostic flow when this code is present.
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1
Connect a scan tool capable of U-code reading; record all stored codes across all modules and note whether U0140 is current or history
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2
Verify BCM fuse(s) and relay are intact and BCM has correct battery voltage and chassis ground at its connector
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3
Inspect the CAN bus wiring harness routing between PCM and BCM for chafing, pinch points, heat damage, or corrosion — pay special attention to firewall pass-throughs
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4
With ignition on, use a multimeter to check CAN High (~2.5 V bias, ~3.5 V dominant) and CAN Low (~2.5 V bias, ~1.5 V dominant) at the BCM connector; a reading near 0 V or 5 V on either wire indicates a short
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5
If wiring checks out, attempt to communicate directly with the BCM using the scan tool; if the BCM does not respond at all, suspect the module itself or its dedicated power/ground supply
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6
Check for technical service bulletins (TSBs) for the specific vehicle — BCM firmware or connector issues are commonly addressed by OEM updates
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7
Replace or reprogram the BCM only after all wiring and power-supply faults have been eliminated and the module is confirmed non-communicative
Related network codes
- U0100 — Lost Communication With ECM/PCM A
- U0101 — Lost Communication with TCM
- U0102 — Lost Communication with Transfer Case Control Module
- U0103 — Lost Communication With Gear Shift Module
- U0104 — Lost Communication With Cruise Control Module
- U0105 — Lost Communication With Fuel Injector Control Module
Frequently asked questions
Can I drive the vehicle with a U0140 code?
The vehicle will usually start and drive, but features managed by the BCM — such as power locks, lighting control, and in some vehicles the immobiliser handshake — may be inoperative or erratic. If the restraint system or anti-theft system is affected, driving should be avoided until the fault is diagnosed.
Will clearing the code make it go away permanently?
Only if the underlying fault is intermittent and self-resolving (e.g. a briefly unseated connector). If the root cause — a wiring short, corroded pin, or failed module — is still present, the code will return as soon as the PCM attempts CAN communication with the BCM again.
How do I know if the BCM itself is faulty versus a wiring problem?
Check whether the BCM has correct power (battery voltage on switched and unswitched feeds) and a good ground first. Then verify CAN-bus voltage levels at the BCM connector. If voltages are correct but the scan tool still cannot establish communication with the BCM specifically, the module is the likely culprit. Module failure is less common than wiring or connector faults.
Does U0140 require the BCM to be programmed after replacement?
Yes, in most modern vehicles the replacement BCM must be programmed (flashed) to the vehicle VIN and options using manufacturer-specific software or a J2534 pass-through tool.
Disabling U0140 in software
RaceTune can permanently disable U0140 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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