U0140
NetworkLost Communication With Body Control Module
You'll usually notice this one through the electrics playing up before you ever see a code. Windows that won't drop, central locking with a mind of its own, interior lights doing odd things, maybe the car refusing to start. Behind all that, the engine ECU has lost its conversation with the body control module over the car's data network (the CAN bus). The BCM runs most of the comfort and convenience electrics, so when the two modules stop talking, all sorts of unrelated-looking faults appear at once.
ⓘ Information only. This page provides general educational information about fault code U0140. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does U0140 mean?
U0140 is a Network (CAN bus, module communications) fault code. It indicates: Lost Communication With Body Control Module.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Several warning lights on the dash at the same time, not just the engine light
- • Electric windows, central locking or interior lighting dead or behaving randomly
- • Wipers or indicators not working as they should
- • Car won't start because the immobiliser thinks it's being nicked
- • Electrical bits cutting out and coming back while you drive
- • Gauges flickering or the dash display dropping out
Possible causes
Causes commonly associated with U0140, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Corroded or chafed wiring on the CAN bus run between the modules, the usual cause and the one that wastes the most diagnostic time
- 2. Loose, dirty or backed-out connector at the BCM, water and road salt love these plugs
- 3. Poor earth or a blown fuse on the BCM power feed, no clean supply means no communication
- 4. Water ingress into the BCM itself, common where the module sits low in a footwell or behind a kick panel
- 5. Failed BCM that's stopped responding on the network altogether
- 6. Corrupt or out-of-date BCM software that needs a reflash after a previous repair or battery issue
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Pull every stored code from all modules, not just the engine. Other U-codes (U0100, U0073) point you toward a whole-network problem rather than a single dead module.
- 2. Get to the BCM and check it for damp, green corrosion on the pins and connectors that aren't fully clicked home. A surprising number of these are solved here with a clean and a reseat.
- 3. Confirm the BCM is actually getting power and a solid earth with a multimeter. A dropped earth mimics a failed module perfectly.
- 4. Measure the CAN bus resistance, around 60 ohms across CAN high and low is what you want to see. A wildly different figure tells you there's a wiring break or short rather than a module fault.
- 5. Try to talk to the BCM directly with a scan tool. If it answers, the module is alive and you're chasing wiring. If it's silent, the module or its supply is the problem.
- 6. Clear the codes and drive it. Intermittent faults that vanish then return usually mean a wiring or connector issue moving with vibration or temperature.
Common questions about U0140
How much am I looking at to sort this out? +
If it turns out to be a dirty connector, a poor earth or a length of chafed wiring, an independent garage will often have it sorted for £80 to £250 once they've found it, with most of that being diagnostic time. A failed BCM is the expensive end. The module itself can be £150 to £500 depending on the car, then you've got coding on top, so a main dealer can easily push the whole job to £600 or more. Always pay for the diagnosis first rather than letting anyone fit a BCM on a guess, because a new module won't fix a broken wire.
How do I know whether it's the wiring or the module itself that's gone? +
The scan tool tells you most of it. If you can communicate with the BCM directly and it reports back, the module is working and you're hunting a connection problem, so go after corroded plugs, the earth point and the wiring loom, especially anywhere it flexes or sits near water. If the BCM is completely silent and you've already confirmed it has battery voltage and a good earth at its connector, that points at the module itself. Intermittent faults that come and go with bumps or weather are nearly always wiring, not a dead module.
Is this something I can have a go at myself? +
You can do the basics. Find the BCM, unplug the connectors, check for corrosion and water, clean the pins and reseat everything properly, and make sure the earth point is tight and clean. That fixes a fair share of these and costs nothing but time. What you can't realistically do at home is test the CAN network properly or code a replacement module, both of which need kit most owners don't own. If a clean and reseat doesn't clear it, hand it to a garage with a decent scan tool.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →