In short
The BSI (as the PSA group, now Stellantis, calls it) or BCM (body control module, in other makes) is the control unit that runs the lights, central locking, electric windows, wipers and much of the communication between modules. When it fails it causes varied, seemingly unrelated symptoms, from lights that stay on to a battery that drains while the car is parked. If it needs replacing, we clone it: we copy its data onto a compatible unit to keep your keys, configuration and vehicle identification. BSI cloning starts from from €100 + VAT (€121 including VAT), at our workshop in Alcalá de Henares or wherever your car is in the Community of Madrid.
Symptoms of a faulty BSI or BCM
The clearest clue is that things with no connection to each other fail at the same time. A broken electric window is a broken electric window; an electric window, the indicators and the locking all failing at once point to the module that controls them all.
| What you notice | Why it points to the comfort module | What to rule out first |
|---|---|---|
| Lights that come on or will not go off by themselves, indicators going haywire | The BSI decides when each lighting circuit gets power | Light switch and the stalk under the steering wheel |
| Central locking that will not open or close, or does so by itself | The module receives the signal from the remote and operates the locks | Remote fob battery and lock motors |
| Wipers that run by themselves or will not stop | The BSI controls their relay and speeds | Wiper stalk and motor |
| Flat battery after a few days parked | The module does not go to sleep and keeps drawing current | A battery in poor condition or an accessory drawing current |
| Random warning lights on the cluster and communication fault messages | The BSI acts as a hub in the communication network between modules | Earths and connectors |
| The car will not start and the immobiliser shows an error | On many models the BSI is involved in recognising the key | Key and immobiliser antenna |
| Electric windows, climate control or radio not responding at once | Many accessories get their power or permission from the module | Fuses |
A weak battery or a loose earth cause very similar symptoms, so a BSI is never replaced without checking that first. That is done with electronic diagnostics of every control unit.
What it is and why everything fails at once
A modern car does not have a switch for each thing: it has modules that receive commands (you press the remote, turn the key, flick the indicator) and decide what to do. The comfort module looks after almost everything that is not the engine or the brakes: lighting, locks, windows, wipers, alarm, power management for other modules and, on many cars, passing messages between the engine network and the body network.
Manufacturers call it different things: BSI on Peugeot, Citroën and DS; BCM or body module on other makes; in some groups the name changes with the generation. The job is the same and, when it fails, a lot fails at once.
The most common causes: moisture, voltage surges (jump starts, an alternator overcharging), internal relays that wear out and solder joints that crack with age and heat.
Clone or repair: how we decide
We do both: repair the BSI internally and clone it onto another unit.
- If the fault is localised (a relay, a track, a connector) and the rest of the module is healthy, we repair it.
- If there is widespread corrosion from water or damage in several areas, the reliable option is to replace it with a compatible unit and clone your data onto it. We source that unit ourselves or you supply it.
- If the memory on yours can no longer be read, cloning is not possible and a new module will have to be programmed with the manufacturer's equipment.
We explain what we see and why we recommend one thing or the other before doing anything.
What is kept when cloning
What goes from your BSI to the replacement
- Keys
- The data of the paired keys, which keep working
- Configuration
- The coded equipment (headlight type, comfort options, language)
- Identification
- The chassis number and the data other modules expect to find
- Mileage
- Copied exactly as it is; never modified
When we finish, the car sees the new unit as if it were the old one. There is no need to reprogram the keys or recode the equipment one item at a time.
A word on mileage: altering it is fraud. Real Decreto 920/2017 (Spain's vehicle inspection regulation), Annex I, section 7.11, classes an odometer clearly tampered with to reduce or falsify the mileage as a major defect at the ITV. We copy the figure that is there, without touching it.
Peugeot, Citroën and the rest of Stellantis
On models from the former PSA group the BSI handles more functions than the body module on other makes, including its role in starting, and it is one of the most frequent body electronics enquiries we get. If you have one of these cars, also have a look at what we say under Stellantis.
On other makes the comfort module may be split across several units, and cloning is approached the same way, unit by unit. For the engine ECU, which is a different job, there is the ECU cloning page.
How much it costs
BSI cloning starts from from €100 + VAT (€121 including VAT). What affects the price:
- The module model and how its memories are read.
- Whether the original unit needs preparation before it can be read (for example, after water has got in).
- Whether we come to you because the car will not start.
Before buying a replacement BSI, send us a photo of both labels so we can confirm they are compatible. You will find all our prices under prices.
Tell us what is failing and since when, and whether the car has had water get in or been jump-started. We will tell you whether it points to the BSI.
Official sources
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