Using DTC Codes to Improve Fleet Maintenance and Repair

Fleet maintenance is especially challenging when check engine lights are not promptly reported. Continuing to drive a vehicle that has an engine problem can lead to much more expensive repairs, not to mention dangerous breakdowns. That’s where remote access to diagnostic trouble codes (DTC) comes into play.

With a robust fleet management system, when an engine or system problem occurs, fleet and maintenance managers can immediately get alerted and view the DTCs (often called DTC codes or fault codes) reported by the vehicle’s onboard diagnostic system (OBD) and take action in real time. An effective, easy-to-use DTC code alert system can make your fleet maintenance and repair program more efficient and cost effective.

What is a DTC code?

A DTC is a 5-character code developed by the Society of Automotive Engineers to characterize specific types of malfunctions in a vehicle or piece of heavy equipment. They are generated by a vehicle’s onboard diagnostic system (OBD) whenever the system detects a fault. To retrieve the codes, a technician connects an OBD scanner to the OBD port.

Even before the trouble is discovered by a technician in the shop, a DTC will cause the check malfunction indicator lamp to come on in the vehicle or equipment.

While OBD DTC standards have gone through several iterations over the decades, there are now two widely accepted standards.

OBD II codes

OBD II codes are used in light and medium-duty vehicles. All cars and trucks built and sold in the U.S. after January 1, 1996 are required to follow the OBD II code standard.

J1939 codes

J1939 codes are used for heavy-duty vehicles and heavy equipment. Large trucks and buses fall under this category.

Manufacturer-specific DTCs

On some vehicles, a few manufacturer-specific DTCs supplement the universal codes. When in doubt as to what code standard is used, check the vehicle’s user manual or ask your equipment dealer. 

DTC meaning: How OBD II codes are created

Thousands of code combinations are possible with OBD II codes. Below is a short primer on what the numbers and letters indicate.

First character: Always a letter, this first character indicates where in the vehicle the issue is occurring.

  • “P indicates a problem with the powertrain
  • “B” indicates a problem with the body (usually, a function inside the passenger compartment)
  • “C” indicates a problem with the chassis
  • “U” indicates a problem with the integrated network or computer controls

Second character: Either a 1 or a 0, this character indicates whether the DTC code is standard (0) or specific to the manufacturer (1).

Third character: This number, which can range from 0 to 7, indicates the subsystem of the fault.

  • 0 points to fuel and air metering (plus auxiliary emission controls)
  • 1 points to fuel and air metering
  • 2 points to fuel and air metering (injector circuit)
  • 3 points to the ignition system
  • 4 points to auxiliary emissions controls
  • 5 points to vehicle speed and idle control
  • 6 points to the computer output circuit
  • 7 points to the transmission

Fourth and fifth character: The final two characters specify the issue and are generally a number between 0 and 99. For example, the number 73 in the DTC code P0573 indicates a high-voltage signal malfunction in the cruise control brake switch.

Leveraging DTC codes in a fleet management system

A vehicle’s telematics device can interpret and send DTC codes from the vehicle’s diagnostic port (OBD-II and J1939) to the fleet management platform. The best fleet management systems translate the codes into plain English, allowing managers to grasp the type and severity of the fault even before the vehicle is brought in for service.

DTC alerts

CalAmp iOn™ allows customers to configure alerts sent via email or text when a fleet vehicle produces a DTC code. Managers can configure alerts for preselected vehicle groups or all fleet vehicles. These alerts, complete with the DTC code and accompanying description, can be configured to go to multiple recipients. 

If a dispatcher or maintenance manager receives a DTC alert, they can make a decision in real time whether to ask the operator to pull over, continue to a service station or complete the route. In the case of an urgent problem such as an overheating engine or low battery, the dispatcher can call the driver to reroute them to the nearest service station and use the location information in the alert to send another vehicle to take over.

With plain-English DTC code descriptions, fleets can not only increase driver safety but also identify vehicle issues before they turn into major repairs.

In iOn, users can choose to receive an alert any time the malfunction indicator lamp is activated as well as any time a DTC is generated.

DTC reports

In addition to receiving alerts, managers can run reports in iOn to see DTC codes across a group of vehicles or the entire fleet. On-demand reports include fault code descriptions, when and where the fault was reported to iOn and the operator and route assigned to the vehicle at the time. These reports allow maintenance managers to view maintenance needs across the fleet and schedule repair on vehicles that need it.

A fleet management system that makes it easy to view and understand fault codes with reports and real-time alerts provides value that drops to the bottom line. It helps managers monitor the health of the fleet, respond faster to engine and system problems, minimize breakdowns and address maintenance issues before they turn into budget busters.

Schedule a demo of CalAmp iOn to see how it can help your organization improve its fleet maintenance and repair.

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