How do DTC codes work?

How do DTC codes work?

If you have a fleet, it’s likely your vehicles are already generating DTC codes (Diagnostic Trouble Codes). DTC codes contain key information about the health of your vehicles and can be used to significantly reduce costs and improve operations.

In this article, we’ll explain how DTC codes work and how your business can benefit from them.

What is a DTC code?

A DTC code stands for Diagnostic Trouble Code and is also commonly referred to as a fault code or as vehicle diagnostics. When a vehicle’s onboard diagnostics system detects a problem, it generates a standardized five-digit code.

The Society of Automotive Engineers (SAE) created standardized DTC codes to help vehicles comply with emission regulations. Put simply, DTC codes make it simple to understand current or potential issues with a vehicle.

How do Diagnostic Trouble Codes (DTC) work?

The OBD-II (in light-duty vehicles) or J1939 (in heavy-duty vehicles) systems constantly monitor the vehicle. When an issue is detected, the OBD-II or J1939 returns the corresponding trouble code. DTC codes are sent to the vehicle’s instrument panel to trigger a warning light, as appropriate.

How to read Diagnostic Trouble Codes (DTC)

DTC codes are five characters long and use a standardized system where each letter and number has a specific meaning. There are thousands of DTC codes, so understanding how to look up the definition of a code is important.

Pro tip: Leading fleet management solutions like KeepTruckin have a vehicle diagnostic feature that interprets DTC codes for you.

The first character in a DTC code will always be a letter and describes the part of the vehicle that has an issue. These are:

  • P – Powertrain. Includes engine, transmission, and associated accessories.
  • C – Chassis. Covers mechanical systems and functions: steering, suspension, and braking.
  • B – Body. Parts mainly found in the passenger compartment area.
  • U – Network & vehicle integration. These are functions managed by the onboard computer system.

The second character will either be a “0” for a standardized code (also known as generic or global codes) or a “1” for a manufacturer-specific code.

The third character is a number that tells you which vehicle subsystem has a fault. Here are the 9 vehicle subsystems:

  • 0 – Fuel and air metering and auxiliary emission controls
  • 1 – Fuel and air metering
  • 2 – Fuel and air metering – injector circuit
  • 3 – Ignition systems or misfires
  • 4 – Auxiliary emission controls
  • 5 – Vehicle speed control, idle control systems and auxiliary inputs
  • 6 – Computer and output circuit
  • 7 – Transmission

If you see an A, B, or C, this refers to hybrid propulsion systems. There can be other families of codes that are manufacturer specific. You’ll need to refer to the definitions your manufacturer provides to interpret these.

The fourth and fifth characters are numbers ranging from zero to 99 and define the exact issue you’re experiencing.

Here’s an example of a complete code:

P0782 means powertrain, generic, transmission, 2-3 shift malfunction.

How DTC codes can be used in your business

DTC codes have been around for decades, but their value has just recently been unlocked. Why? In the past, a mechanic had to manually connect to the onboard computer to capture DTC codes. While this was helpful, the impact was limited, as issues that occurred between trips to the shop weren’t actionable.

Today, fleets of all types are adopting telematics systems (sometimes in the form of ELDs). A telematics system captures DTC codes, interprets them into clear descriptions, and sends them to fleet management solutions in real-time.

Fault Codes - KeepTruckin Dashboard

Here are a few of the most common ways that fleets are using DTC codes:

Proactively plan maintenance. When vehicles are taken into the shop, you can provide mechanics with historical fault code reports for the vehicle. This allows them to identify and fix every issue in a single appointment and avoid future breakdowns or downtime.

Identify critical issues in real-time. You can choose to receive real-time alerts for critical vehicle issues and ensure the vehicle is taken off the road before it causes an expensive breakdown or, worse, an accident.

Fleets that use DTC codes to proactively plan maintenance often report seeing the following benefits:

  • Lower total maintenance and repair costs
  • Reduced out-of-network maintenance and towing expenses
  • Fewer breakdowns and a higher on-time delivery percentage
  • Increased fuel economy
  • Decreased vehicle violations during roadside inspections, which improves CSA scores

Start using your DTC codes today

It’s likely that your vehicles are already generating DTC codes that contain key information about the health of your vehicles. If DTC codes are managed and utilized correctly, they can help reduce costs and improve how your business operates.

Learn more about DTC codes.

Disclaimer: All content and information on this website is for informational and educational purposes only, does not constitute financial, business, or legal advice. Although KeepTruckin strives to provide accurate general information, the information presented here is not a substitute for any kind of professional advice, and you should not rely solely on this information. Always consult a professional in the area for your particular needs and circumstances prior to making any professional, legal, business and financial or tax-related decisions.

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