What Are BSI and BSM Modules? Failure Symptoms in Peugeot and Citroen

In Peugeot and Citroen (PSA) vehicles, the electrical system is built around two main modules: the cabin BSI and the engine-compartment BSM. A problem in one of these modules can cause many seemingly unrelated electrical faults.

What is the BSI?

The BSI is the central unit that manages the vehicle's body electronics. Functions such as central locking, lighting, wipers, windows, communication with the instrument cluster and the immobilizer run through the BSI. It also houses the cabin fuses.

What is the BSM?

The BSM is the smart fuse and relay box in the engine compartment. It controls the power supply lines for the fan, starter, headlights and engine management. It is a frequently replaced part on models such as the 207, 307, 308, 3008, Berlingo and Partner.

Fault symptoms

• Central locking, turn signals or headlights operating on their own or not working at all
• Battery draining overnight
• Many warning lights in the instrument cluster when the ignition is switched on
• Wipers, fan or horn operating uncontrollably
• Engine not cranking or an immobilizer warning

Common causes

Water ingress and moisture, voltage spikes during battery replacement, and relay and solder fatigue are the most common causes. Water leaks from the windshield in particular can damage the BSI.

What to check before replacement

• The BSI number and version must be compared exactly. Example versions: BSI 2004, BSI 2010, BSM R02, BSM R05.
• After replacing the BSI, pairing with the keys and engine ECU may be required.
• For water-related faults, the source of the leak must be fixed before the new module is installed.

For models in stock, visit our body control module (BSI, BSM, UCH, BCM) products to see what's available.

FAQ

What is the difference between the BSI and BSM?

The BSI is the central electronic unit in the cabin and manages comfort functions. The BSM is the fuse and relay box in the engine compartment. The two communicate with each other.

Will the car start after replacing the BSI?

In PSA vehicles, the BSI holds the immobilizer data. That is why pairing with the keys and engine ECU is usually required after replacement.

How do I know which BSI fits my vehicle?

Compare the number in 96xxxxxx80 format on the BSI label and the BSI version. You can request a free check by sending a photo of the label.