Out of 96 coded diagnostics in our US platform data, the most common fault family isn't emissions or engine performance, it is transmission faults, led by P0420. We see a completely different picture when we look at European shops. We recently pulled a sample from our own platform data covering 1596 diagnostics that included at least one readable fault code, drawn from a total of 2908 diagnostics recorded between February 18 and September 5, 2026.
The European Underboost Problem
In our dataset, P0299 (Turbocharger underboost condition) is the undisputed king in several major European markets. In Sweden, out of 1003 coded diagnostics and 1632 code instances, P0299 is the top code. The most common family is Powertrain, specifically manufacturer-specific codes. We see the exact same pattern in Great Britain, where P0299 leads across 184 coded diagnostics and 346 code instances. Romania follows suit, with P0299 topping the list across 49 diagnostics and 70 code instances.
This data represents the vehicles rolling into independent workshops on our platform. The prevalence of underboost codes in these regions points to a heavy reliance on turbocharged powertrains, likely driven by regional fuel economy standards and fleet compositions.
The American Anomaly
The US data tells a different story. Across 96 coded diagnostics and 178 code instances, the most frequent code is P0420 (Catalyst system efficiency below threshold, bank 1). What stands out in our platform data is that the most common fault family for this US sample is Transmission. The vehicle mix and local driving conditions clearly shift the diagnostic workload away from turbocharger issues and toward catalyst and transmission concerns.
Timing, Misfires, and Communication
When we look at smaller samples in other countries, the primary faults fragment further.
| Country | Diagnostics | Top Code | Most Common Family |
|---|---|---|---|
| Italy | 22 | P0017 (Crankshaft/camshaft position correlation, bank 1 sensor B) | Valve timing and camshaft |
| Denmark | 14 | P0300 (Random or multiple cylinder misfire detected) | Misfire |
| Lithuania | 17 | P0135 (O2 sensor heater circuit, bank 1 sensor 1) | Bus communication |
| Poland | 14 | P0322 (Ignition or distributor engine speed input circuit, no signal) | Ignition and knock sensing |
In Germany, across 42 coded diagnostics, the top code is B2010, dominated by manufacturer-specific powertrain codes. Bulgaria shows P208E as the top code across 20 diagnostics. The workload changes dramatically depending on the specific fleet rolling through the bay doors.
What You Are Seeing
The vehicles in your bay dictate the tools and knowledge you need on hand. I am curious how closely our platform data matches your daily reality. Are you spending most of your week chasing P0299 underboost faults, or is your shop overwhelmed with catalyst efficiency codes?