REMOTE DTC READING FOR PROACTIVE HEAVY FLEET MAINTENANCE

INTRO

Diagnostic trouble codes (DTCs) are standardised alerts generated by the vehicle’s electronic control unit when issues are detected. Each code contains information about the type and location of a fault, helping technicians identify issues more quickly. With Teltonika PROFESSIONAL category trackers, reading fault codes from heavy vehicles can be automated, enabling remote diagnostics and proactive fleet management.

CHALLENGE

Most fleet operators only become aware of component failures when the check engine light appears on the dashboard, which is often too late for preventive action.

Take, for example, a long-haul truck showing early signs of trouble: a slight drop in power, rough idling, and inconsistent fuel consumption. The driver hears a faint knocking sound but sees no warning indicators. With limited information, they contact the dispatcher to assess whether the journey should continue. This moment of uncertainty reflects a broader issue; without access to live diagnostic data, operators are left to interpret symptoms without context.

In this case, the underlying fault is a deteriorating injector, which gradually affects combustion quality. Over time, the problem escalates, leading to incomplete fuel burn and increased cylinder wear. If unnoticed, the vehicle continues operating inefficiently, consuming more fuel and placing additional strain on engine components.

Eventually, the fault triggers a warning light, forcing the truck off the road for repairs. The vehicle may require towing to the nearest service centre, which often leads to unexpected expenses. In such cases, service rates may be higher in some regions due to local pricing, lack of prior relationship with the workshop, or urgency of the repair. There is also no guarantee that the mechanics are reliable or familiar with the vehicle’s specifications.

Non-operational time is costly as well. Long-haul trucks typically cover between 273 and 411 kilometres per day, with freight rates ranging from €1.10 to €2.30 per kilometre depending on the route and country. Even a single day of downtime can result in lost revenue of up to €945, not to mention disruption to delivery schedules and customer commitments.

The real challenge lies not in the fault itself, but in the absence of early visibility. Without real-time diagnostic data, operators cannot distinguish between minor irregularities and emerging failures. This lack of clarity often leads to reactive decisions, which are more costly and less predictable than planned interventions.

SOLUTION

To address this, Teltonika’s PROFESSIONAL FMx6 series trackers can read DTCs directly from heavy-duty vehicles, helping fleet managers identify issues before they escalate.

FMC650 tracker uses the SAE J1939 protocol, which standardises communication between electronic control units in heavy vehicles. This enables easier diagnostics, data logging, and interoperability across systems. The standard also defines diagnostic messages for reporting and repair. The most important of these is DM1, which provides real-time insight into current vehicle faults; thus, it is often referred to as active diagnostic trouble code.

DM1 contains two key components that help evaluate the vehicle’s condition:

• Signal lamp status – indicates whether dashboard warning lights are triggered. These help fleet owners assess whether a fault is severe enough to stop the vehicle or if it is a minor issue that can be addressed later.

  
  

• Diagnostic trouble codes, which describe each fault using:

o Suspect Parameter Number (SPN) – identifies the affected system or component

o   Failure Mode Identifier (FMI) – describes the type and severity of the fault

o   Occurrence Count (OC) – shows how frequently the issue has occurred

o   Conversion method – indicates whether the SPN follows a standard or proprietary format

Think of active diagnostic messages as a continuous broadcast of vehicle issues, and telematics as the tool that allows you to tune in. This broadcast reports everything in real time, from minor irregularities to serious faults. Without listening to it, operators rely solely on dashboard warnings like the check engine light, which provides information about neither the location nor the severity of the malfunction.

In addition to DM1, FMx650 devices also capture DM2 messages, which contain previously active faults. These help identify recurring issues and long-term fault patterns.

To ensure maximum flexibility, FMx650 trackers transmit diagnostic messages as raw hexadecimal strings without applying any pre-interpretation. These messages are identical to what a service tool would read at a workshop, giving integrators the choice to build their own decoding logic or simply forward the codes to fleet owners who often already know their meaning.

Predictive maintenance with FMx650 doesn’t stop with diagnostic message insights. The tracker can connect two CAN lines, which unlocks vehicle data from different sources. Whether it is managing the best route to the workshop based on the driver hours left on the tachograph or monitoring tyre pressure from the trailer EBS modulator, the tracker can handle it all.

By combining active fault codes with other CAN data, operators gain a comprehensive view of vehicle health. This makes it possible to schedule maintenance proactively, reduce unplanned downtime, and extend the lifespan of a truck.

TOPOLOGY

BENEFITS

• Remote diagnostics – Eliminate manual diagnostics and enable faster, more scalable maintenance workflows, giving businesses a competitive edge through smarter fleet management.

  
  

• Reduce fleet downtime - By detecting faults early, fleets can plan service before breakdowns occur. This minimises repair delays and keeps vehicles on the road longer.

  
  

• Optimise maintenance processes - Remote DTC reading allows technicians to prepare parts and service in advance. As a result, workshop time is shortened, and maintenance becomes more efficient.

  
  

• Lower operational costs - Vehicles running outside optimal conditions consume more fuel and wear out components faster. Accurate fault data helps operators avoid costly inefficiencies and extend vehicle lifespan.

  
  

• Enable data-driven decisions - DTC insights give managers a clear view of vehicle performance under different conditions. This makes it easier to plan budgets, schedule service, and decide on upgrades or parts replacement.

  
  

• Scale telematics with fewer devices - Instead of installing separate hardware for diagnostics, tachograph, and FMS data, the FMx650 integrates everything into one solution. This reduces complexity, installation time, and overall costs for fleets and integrators.

WHY TELTONIKA?

Teltonika has years of experience in developing reliable and innovative solutions for vehicle data management. PROFESSIONAL category trackers are a reflection of this expertise, offering advanced data collection features and regular firmware updates.

By choosing Teltonika, users benefit from robust hardware built for demanding fleet operations and a wide range of features including DTC reading, remote tachograph files download, driver behaviour analysis, and trailer EBS data reading. Dedicated implementation support ensures smooth integration across markets.