Three tests produce three different results for diesel car

A Latvian driver received widely differing particulate-filter readings at vehicle inspections and a diagnostic test, LSM reported, raising questions about how the results can vary.

From 2026, diesel cars first registered in 2013 or later will fail their technical inspection if their particulate-filter emissions exceed the limit of one million particles. Renars’s car recorded four million particles at an inspection station in Ventspils.

A month later, before returning for a reinspection, Renars had the car checked in Riga. The reading was below one million. At a second test at the Ventspils inspection station that same day, it rose to 10 million.

Renars said he was told the filter needed to be replaced, despite the diagnostic test showing a result within the limit. Convinced the car was in good condition, he bought a one-day permit to drive and went to an inspection station in Kuldiga the next morning. Its device recorded 980,000 particles, within the permitted level.

After Renars shared his experience on social media, drivers from other Latvian cities said they had encountered similar problems and questioned the readings.

Gundars Zalcmanis, an associate professor at Riga Technical University’s Faculty of Civil Engineering and Mechanical Engineering, said such a large difference should not occur if no repairs had been made to the car. If the actual reading were one million, he said, a result of 1.2 million or 800,000 could be expected.

Zalcmanis said highly precise equipment is needed to measure particle counts accurately, and that such devices are available at laboratories certified by car manufacturers.