F633 - Internal fault, passenger airbag stage 1 firing circuit airbag control unit fault

What does error code F633 mean in the airbag control unit?

Error code F633 reports an internal fault in the ignition system of the passenger airbag, specifically in its first stage. This directly affects the ignition system of the passenger airbag as part of the restraint system (SRS), which triggers the airbags in an accident and is controlled by the airbag control unit.

The airbag control unit stores the fault in the fault memory and switches on the airbag warning light. The airbag warning light thus shows that there is a fault in the restraint system.

How do you recognise error code F633?

You recognise error code F633 mainly by the airbag warning light staying on permanently and the code being stored in the fault memory of the airbag control unit. It cannot be permanently erased from the fault memory, and the airbag warning light stays on until the fault has been properly resolved.

Have the code read out with a diagnostic tool. Only then can it be narrowed down whether the ignition circuit itself or the control unit is affected.

What causes error code F633?

Error code F633 occurs when an internal fault arises in the ignition system of the passenger airbag and is then stored in the control unit. The possible causes are connectors, wiring, the airbag module of the passenger airbag and the airbag control unit itself, but also crash data after an accident or aged electronic components.

• Connectors or wiring to the passenger airbag are damaged or corroded.
• The airbag module of the passenger airbag is faulty.
• Crash data from an accident is stored in the control unit.
• Aged electronic components or solder joints in the control unit are faulty.
• Voltage spikes from a weak battery or jump-starting can strain the electronics.

Which of these parts is affected can only be established by a detailed check in each individual case.

In which vehicles does error code F633 occur?

Error code F633 is so far known in Citroën vehicles, namely in the models C3 Aircross III, C3 Picasso I, C4 Aircross I, C4 Cactus I, C5 Aircross II and ë-C3 IV. The list is not complete, because not every vehicle that can show the code has been recorded.

The meaning may differ on other vehicles. If in doubt, only an individual check will establish whether your vehicle is affected.

How is error code F633 resolved?

Error code F633 is resolved by first having the fault memory read out with a diagnostic tool and then having the cause checked at a specialist workshop. If the cause lies in the control unit itself, the unit is removed after the battery has been disconnected and sent to Airbag24 for repair.

First have the fault memory read out with a diagnostic tool. If connectors, wiring or the airbag module of the passenger airbag come into question as the cause, have these checked at a specialist workshop first.

If the cause lies in the control unit itself, for example in internal faults or crash data, the battery is disconnected first and the control unit is then removed. Then create a repair order online and send the unit to Airbag24. Checking, repairing and testing usually take 3–4 working days. The repaired control unit comes back with all vehicle data and is ready for use as soon as it is refitted — no coding or programming is required.

Work on the airbag system should be left to qualified specialists.