Typical BSI faults on Peugeot and Citroën: catalogue, symptoms and repair

Summary: The BSI (Boîtier de Servitude Intelligent) is the body control unit of PSA models (Peugeot, Citroën, DS, and since 2010 also Opel). It is the module that causes the most faults in these cars, more than any other electronic component. Learn to identify its 7 most typical failures and what can be repaired.

What exactly is the BSI

The BSI is the central body computer: it manages the lights, central locking, air conditioning (on some models), immobiliser, communication between ECUs, power supply to the secondary modules and, on recent models, the vehicle's multiplexed CAN network.

Unlike the engine ECU (which changes little between versions), the BSI has dozens of variants per year, engine and equipment level. This explains why a "compatible" second-hand BSI rarely works unless it is cloned or coded to the car's VIN.

PSA models where the BSI is problematic:

• Peugeot 207, 308 (T7), 3008/5008 (P84/P87)
• Peugeot Partner Tepee and 207 SW
• Citroën C4 (B7), C3 II, C5 (X7), Berlingo II
• DS3, DS4, DS5

The 7 most typical PSA BSI failures

1. Parasitic drain (battery goes flat overnight)

Symptom: the car runs out of battery for no apparent reason every 2–4 days. You fit a new battery and it keeps happening.

Cause: the BSI does not enter sleep mode because a CAN module stays "awake". The BSI itself can be the cause when its internal software has a bug or when an internal capacitor has degraded.

Repair: cloning the firmware with a newer version, or replacing capacitors in the internal power supply module.

2. Erratic central locking

Symptom: the car unlocks by itself, locks by itself, or the locks "jump" while driving.

Cause: worn internal BSI relays or oxidised communication terminals to the locks.

Repair: replacing the relays on the board (typical service, €80–150).

3. "The car doesn't recognise my key"

Symptom: the key works sometimes and not others. Sometimes it doesn't unlock, other times it unlocks but the car won't start.

Cause: faulty transponder antenna inside the BSI or corrupt EEPROM where the list of authorised keys is stored.

Repair: antenna repair + EEPROM rewrite. Important: do NOT buy a new key without diagnosing the BSI first — you will spend money without solving anything.

4. Main display off (radio, climate control)

Symptom: the instrument cluster works but the central screen is black or flickering.

Cause: on some models, the BSI powers the display. The power line is lost inside the BSI.

Repair: replacing an internal fuse or restoring a track (depends on the model). €60–120.

5. "Ghost" lights (indicators, reversing lights, fog lights)

Symptom: a light comes on or stays on without any action from the driver.

Cause: short-circuited internal relay or BSI output with a leaking MOSFET.

Repair: replacing the corresponding output MOSFETs.

6. Total failure (the car is "dead" — it won't even open with the key)

Symptom: the car does not respond to the key, nothing on the dashboard lights up, not even the interior when you open it with the emergency key.

Cause: BSI with a dead CPU, usually due to overvoltage (changing the battery with reversed polarity is the most common case).

Repair: on some models, recovery via BDM/Boot. On others, it requires cloning to a physically compatible donor BSI.

7. Loss of communication with the engine ECU

Symptom: the OBD scanner sees the BSI but not the engine ECU.

Cause: faulty CAN line inside the BSI (the BSI acts as a CAN "switch" on many PSA models).

Repair: repairing the BSI's internal CAN driver. €90–180.

Why do they fail so often on PSA?

There are three main technical reasons:

1. Module location: on most PSA models, the BSI is under the dashboard on the driver's side, at a point where moisture from the heating/AC condenses and drips onto the board.
2. Cheap electrolytic capacitors: the 2003–2010 BSI versions (especially Sagem) use capacitors that age badly.
3. Buggy software: PSA took years to stabilise the BSI firmware; early versions (T1, T2, T3) have incompatibilities with later modules.

Summary table: symptoms vs. estimated cost

Repair it or replace it?

If you find a second-hand BSI on the internet, remember:

• NOT plug & play, except in rare cases.
• It needs to be cloned to your VIN to replace the original.
• The price of a used BSI + cloning service usually equals or exceeds the cost of repairing yours.

In most cases, repairing your original BSI is faster, cheaper and keeps it consistent with the car's other modules.

How to send your BSI for repair

1. Locate the module (in the driver's pedal area on most models).
2. Remove it, disconnecting the connectors carefully.
3. Send it by courier in anti-static packaging (we will send you one free of charge if you call us).
4. Within 48–72 working hours we return the repaired BSI to you, ready to refit without additional coding.

Related services: BSI repair · ECU repair · ECU cloning

Last updated: 18 May 2026.