2010 Peugeot 207 ESP/ASR system faulty

First consider if the steering shaft was turned while the clock spring was removed. If it was turned a full revolution, then the clock spring was reinstalled, it will have reached the end of its travel before the steering wheel did in one direction. That will either tear the internal ribbon cable or it will fold back over on itself repeatedly until it breaks.

If you think the clock spring remained centered to the steering shaft, also consider if the ignition switch was turned on while the air bag was disconnected. That will set a fault code and turn on the warning light. You may not be able to erase that code by disconnecting the battery. You may need to find a mechanic with a scanner that can access the various computers. Before trying to erase any codes it is real important to have them read so you know what the computer detected. Once you know the circuit that set the code, you can decide if there's a real problem or if it was simply caused by something you did.

How can I find out if the internal ribbon was broken? Ofc I do not want to disassemble whole element.

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