I'd agree that check the exhaust for leaks / air ingress is a good idea and I'd also suggest to plug the car into scan tool so you can pull off the fault code
as this will point more directly at the issue and save a lot of time in repairs
another possibility is this may be an issue with the FAP system
In the exhaust is a soot filter known to PSA as a FAP. It runs very hot to burn some of the soot off every few thousand miles. It uses an additive is called Eolys and is stored next to the diesel tank with a computer controlled dosing mechanism.
If you don't drive it long enough, fast enough; then the regeneration process won't commence and the filter will block. Take it for a 40 minute blast down a empty dual carriageway; As you need to maintain above 50mph for around six minutes - that will start the process.
Alternatively; take it to your dealer or Peugeot specialist for a forced regeneration. If it's done more than 50,000 they will probably just fit a new FAP and top up the additive. this will cost £6-800.
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