Networkcar announced this week the results of an analysis of diagnostic trouble codes (DTC) gathered from thousands of commercial vehicles across the U.S. that use its Networkfleet wireless vehicle management system. Networkfleet continuously monitors and collects data directly from a vehicle's engine computer and from a global positioning system (GPS). An analysis of aggregate Networkfleet data shows that 47 percent of diagnostic trouble codes for light/medium duty (OBD-II) vehicles were related to emissions issues and 24 percent were related to fuel consumption issues. The Networkfleet system consists of an in-vehicle unit that wirelessly transmits diagnostic and GPS data. Fleet managers access a Web-based application to view specific vehicle data such as current location, fuel consumption, mileage, speed, and idle-time. Networkfleet automatically notifies fleet managers by email immediately when a vehicle reports a diagnostic trouble code (DTC). Networkfleet provides the precise DTC code and a description identifying the specific nature of the problem. This allows technicians to procure parts ahead of time and begin working on the problem immediately instead of spending time trying to determine what is wrong. Each month, Networkfleet intercepts 30,000 to 40,000 DTC codes from thousands of vehicles in fleets across the U.S. The top three individual diagnostic trouble codes collected by Networkfleet include: * #1 Light Vehicle DTC (P0300) is related to cylinder misfires. Misfires can be indicative of poor maintenance or of a faulty or worn ignition system. * #2 Light Vehicle DTC (P0171) indicates that the air to fuel mixture is suboptimal. This could be indicative of a faulty O2 sensor or a faulty/worn fuel pump. * #3 Light Vehicle DTC (P0420) indicates that there may be a problem with the vehicle catalyst and that it should probably be replaced. "For fleet managers, nothing is more important than keeping vehicles running and productive. Maintaining vehicles, including both repair and upkeep, can have a huge impact on a fleet’s bottom line,” said Paul Washicko, president of Networkcar. “Networkfleet enables them to have a proactive, preventive maintenance program and fix vehicle problems before they escalate into larger issues.”
What Are the Most Common Vehicle Diagnostic Trouble Codes?
Networkcar gathered data from onboard computers of thousands of commercial vehicles using Networkfleet.
More Small Fleet

Boosting Last-Mile Fleet Uptime, Safety, and Value with AI Vehicle Inspections
AI-powered inspections are transforming last-mile fleets by replacing manual checks with highly accurate automated scans that detect defects in seconds. By giving fleet operations visibility into the daily condition of their vehicles, you can identify trends over the vehicle’s lifecycle that enable improved procurement decisions, route management, driver training and accountability.
Read More →How One Fleet Cut Motor Pool Costs by $45K With Smarter Key Control and Automation
Still managing your motor pool with spreadsheets and manual approvals? Loyola University replaced outdated processes with automated fleet management, eliminating overtime and saving up to $50,000 annually. See how they did it.
Read More →Artificial Intelligence in Field Service: North America
48% of field service leaders are investing in AI to manage customer communication and self-service. Get the latest on how fleets are using AI and thinking about the future.
Read More →
Five Ways Seat Belts Help Prevent Injuries
There are five ways seat belts protect occupants from injuries, according to the Tennessee Department of Safety and Homeland Security.
Read More →
It’s here: The 2026 Fleet Technology Trends Report
What does AI mean for fleets? Get the answer — and learn other top tech trends.
Read More →
Small Fleets, Big Impact: How Independent Drivers Power Wreaths Across America
Check out how small fleets and independent drivers power Wreaths Across America each December and why their impact matters more than ever.
Read More →
VMS Survey Finds 65% of Small Fleet Managers Run Operations Alone
A new VMS survey shows small fleet managers are stretched thin, with most handling operations solo and eager to adopt digital tools for relief.
Read More →
Tips for Driving Safely on Halloween Night
This video features a reminder from the Connecticut Department of Transportation (DOT) and the Connecticut Police Chiefs Association, urging drivers to prioritize safety this Halloween.
Read More →
AI, Access, and Uptime: VMS’s Next Chapter with David Prusinski
VMS’s new Co-CEO, David Prusinski, shares how an AI-first approach will give small fleets and repair shops the tools to compete like big players.
Read More →
Fleet Managers Share Winter Prep Tips: It's Never Too Early!
Three fleets share best practices to prep vehicles for winter and prevent downtime when the cold sets in.
Read More →
