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I received an invitation from Peugeot asking me to bring a 2018 naturally aspirated gasoline engine Peugeot 208 (61 kW) to the workshop for a firmware update fixing lamba sensor management which otherwise results in higher than allowed NOx emissions.

What effects should I expect as result of such update?

Lower max torque (and therefore power) and overall higher fuel consumption (due to a richer mixture), only lower max torque, or only higher overall fuel consumption?

I wonder whether I can, if desired and meaningful, refuse the update.

Edit: the reasoning behind is: if lowering NOx emission produced advantages from a driver or advertisement point of view, they would have done it in the beginning or they would have pointed it out very clearly in the letter. Since the change comes after the purchase and no advantages beyond emissions are listed, it will likely worsen some aspects that they expect me to care about.

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    The effects on a diesel engine which you quote, especially a VW diesel when you have a Peugeot, will not be relevant for your gasoline engine. – Solar Mike Nov 7 '19 at 12:21
  • Why would you want to refuse it? You are extrapolating side effects from unrelated engines, why don't you ask the dealer? – GdD Nov 7 '19 at 12:33
  • @SolarMike the link about Diesel was misleading, I removed it altogether. I added the reasoning behind my question. – FarO Nov 7 '19 at 12:41
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    It may not necessarily be the case that this update will affect WOT performance. It might only be for closed-loop, cruising operation. I won't deny the possibility that the update might "detune" your car - I agree that's a valid concern, but there's no way to come to a conclusion without knowing the exact details of the update. And it doesn't seem like anyone here does. – Kitsunemimi Nov 7 '19 at 14:09
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    Something you could consider is whether this update will be included in all new models going forward. If that is the case, then you could look for the 2020 model - if it has the same engine and the same power figures, then there's a chance that the update won't affect power, otherwise that could be considered false advertising. That being said, it's still not conclusive because rather than being overrated after the update - and unfairly advertised, it may simply be underrated before the update. – Kitsunemimi Nov 7 '19 at 14:15
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If the fix is to keep the oxygen sensors working, in normal operation you won't notice anything. If the sensors were to become unavailable (i.e. a car in an unpatched state) you would see poor performance, poor fuel economy and reduced catalytic converter life. The final risk is that it would cause the vehicle to fail it's annual MOT emissions test. Also, if the sensors give incorrect readings, you run the risk of your engine going lean which may ultimately cause engine damage such as melted piston crowns.

The purpose of the oxygen or lambda sensor array is to allow the engine to trim it's fuel towards a Stoichiometry ideal (around 14:1 in a petrol engine) which means you burn all of the fuel injected fully without creating undue heat. Essentially the same as adjusting the mixture on a traditional carburettor engine but with the exception that you are able to make realtime adjustments digitally based on actual engine cycle data.

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