The Catalan Tax Agency (ATC) is also wrong. It can happen to anyone; but if the error involves paying more than the account, it hurts. This is what happened to Sergio Lainz, a taxpayer who has had a long experience until the Treasury recognized the error, as he was asked to pay two and a half times what he was entitled to for the CO2 tax on his car. “I ask other taxpayers to check their notifications because they may be paying more for CO2 tax than they should,” says this retired photographer.

Lainz went on a journey to gather the evidence that confirmed his suspicions. In his case, the alarms went off after he received a notification requiring him to pay 228.7 euros for the CO2 tax on his vehicle (a 2005 petrol BMW). It seemed to him that the sum was excessive and he went to complain to the Agency’s offices. There, an official told him that the period for reviewing the vehicle register had passed and that the fee to be paid is set by the ATC with the emissions information sent to him by the General Directorate of Traffic (DGT). And so began his pilgrimage…

In order to support the appeal he wanted to present, he went to the DGT with the intention of having them certify what the real emissions of his car were; and there they told him that since it was a pre-2015 vehicle, it did not have the data sheet with that information. He then went to a BMW dealer but the price for the certificate was so exorbitant (more than 200 euros) that he rejected the proposal. Even, in his Kafkaesque journey, he went in vain, with the same claim, to his ITV.

Until, after many unsuccessful steps, he learned that he could check the actual emissions of his vehicle by comparing them with the PDF lists published by the Institute for Diversification and Energy Saving (IDAE), where all the models and car versions, accompanied by their corresponding CO2 emissions.

And from that review, he detected the error. ATC had assigned his BMW 356 g/ CO2/ km, while his car model emitted 225 g/ CO2/ km. “They charged me as if my car were the most expensive in the BMW range on the IDAE list”, he complains, convinced that this mistake can be repeated in other taxpayers.

Thus, he gathered the evidence, filed an appeal and won, so he had to pay much less: 87 euros.

But his surprises did not end there. Having already become an expert in the field, he found that the tax pattern simulator estimated that he had to pay 90 euros. And yet, they charged him less! Because? In the resolution to his appeal, the ATC indicates that (to set the fee to be paid) an estimate was made based on the logarithm designed by the Barcelona Supercomputing Center (BSC), a formula provided for in the law, which takes into account the category, type of fuel and others.

And new paradox! What he ends up paying (the 87 euros) is just the amount of the emissions that, as he later discovered, the instruction book of the car he bought tells him: “that document that no one ever reads”, he says .

Sources from the Department of Economy and Finance put a lot of emphasis on stressing that every May a provisional register with vehicle data is published (for citizens to check), since many times the information on the emissions of CO2 comes from the DGT.

Specifically, the DGT provides information on the CO2 emissions of all new vehicles (with a technical data sheet, mandatory for all vehicles registered since 2015); and, in the case of vehicles prior to 2015, it often provides the information offered by the IDAE guides. When this is not the case, it is the Tax Agency that incorporates the IDAE data. And finally when this information is not available (for whatever reason), the ATC estimates the CO2 emission based on the logarithmic formula of the Barcelona Supercomputing Center.

The ATC does not report on the particular files, and everything indicates that in this case the error was probably due to the fact that the data with the IDAE guides and their car lists are not as accurate as would be required, since there there are many car models with different characteristics (according to displacement, engine…), which makes it possible that there may be incorrect automatic entries.

The Tax Agency describes as anecdotal the number of allegations that are presented against the CO tax, which is why it considers that its application is being correct. In 2023 there were only 66 allegations against this tax in a fleet in Catalonia of 4.8 million cars: 0.0015% of the total. Of the vehicles registered in the provisional register, 50% had a technical data sheet, in 35% of the cases the information was obtained from the IDAE guides and in the remaining 15% the resulting quota was calculated from the formula of the BSC. That has proven to be infallible here.