Judder and flat spots when accelerating on Euro 6b 1.5 dCi and 1.6 dCi engines after the 2024 emissions update

Engine / equipment

Renault and Dacia Euro 6b 1.5 dCi (K9K) and 1.6 dCi (R9M)

Period mentioned

Cars that received the NOx-reduction update of early 2024

Symptoms

After a visit to the dealer, flat spots when accelerating and judder at steady speeds; sometimes higher diesel consumption. On the Mégane IV and Kadjar the engine may start and then stall.

Possible cause described

In early 2024 Renault and Dacia updated these engines to cut nitrogen oxides (NOx) further. According to an internal Renault technical note from June 2024, updated in February 2025 and reported by L'argus, the flat spots and judder are mainly due to the new strategy widening the periods when the NOx trap is cleaned (regenerated); to do so the engine injects more diesel, which also explains the higher consumption.

Check for the garage

Ask a Renault or Dacia dealer for the new injection ECU reprogramming for these symptoms (Dacia has offered it since May 2024 and Renault since January 2025). It is not a recall with a letter: you have to ask for it. First have them rule out other causes (particulate filter, boost pressure sensor).

Cost cited in the source

No verified estimate: the note does not say whether the reprogramming is free; ask the dealer.A rough figure from the original database, not an up-to-date quote.

Sources from the original database