GPS for transport fleets: what to look at (and what to ignore)

The "just locate" problem

A GPS without bus reading tells you where the truck is and little else. For a transport fleet, that is 20% of the value. The other 80% lives in real consumption per route, driving hours vs. paid hours, driver identification and auditable eco-driving events. Without J1939 and tachograph, you are paying for a tracker.

The right approach: wired device with native CAN + tachograph reading + independent LLS fuel sensors for cross-checking. Three sources, one truth.

Reading the J1939 bus

J1939 is the standardised CAN protocol for heavy vehicles (SAE J1939). The PGNs you care about ride on it:

• Instantaneous and cumulative consumption (litres, l/100 km).
• Engine RPM and load percentage.
• Speed and real odometer (no odometer tampering).
• Coolant temperature, oil pressure, AdBlue.
• Engine brake, retarder and PTO status.

The FMC650 reads it out of the box: plug the J1939 connector into the corresponding truck port (no external CAN-CONTROL needed) and the PGNs arrive parsed at the server over Codec 8 Extended.

Digital tachograph: reading and remote download

For tractor units and trucks >3.5 t, the digital tachograph is a legal obligation. The FMC650 covers two things:

1. Real-time reading of driver activity (driving, rest, other work, availability). The fleet manager sees what each driver is doing without waiting for the weekly download.
2. Remote DDD download of the C (driver card) and M (mass memory) files. No manual plugging, no driver trips to the office.

This removes the admin friction of "the driver forgot to bring the card on Friday". And leaves full legal traceability, with a server-side timestamp.

Complementary sensors

J1939 covers almost everything, but there is data where the bus lies or does not expose it:

• Capacitive LLS probe in the tank, connected via RS485. Detects diesel theft (sharp level drop with the vehicle parked and the engine off). J1939 gives you consumption, but it does not catch a theft in the car park.
• BLE temperature probes for refrigerated transport: up to 4 per device, no extra wiring.
• Driver identification via iButton or RFID, complementary to the tachograph card (for short moves without tachograph obligation, e.g. yard manoeuvres).
• ADAS camera if the insurer requires a DVR or if you have had recent incidents.

ROI calculation: three real levers

The ROI of a GPS in a heavy fleet is quantified, not guessed at. Three common levers:

1. Consumption reduction through eco-driving

Harsh acceleration, prolonged idling and over-revving events drop by 5% to 12% in the first 6 months when there is weekly reporting to the driver. On a fleet of 20 trucks consuming 30,000 l/year each, a 6% reduction is 36,000 l/year.

2. Optimisation of driving hours

Cross-referencing tachograph activity with the route sheet: you identify idle time, billable waits at the customer and real overtime. Typical recovery: 3–5% of unproductive hours turned billable or avoided.

3. Preventive maintenance

J1939 DTCs + real odometer + engine hours let you schedule services at real kilometres, not estimates. Reduces roadside breakdowns and stops at non-partner workshops.

In practice, an FMC650 + LLS probe + fleet server install pays back in 6–10 months for fleets of 10 trucks or more. Below that, the cut-off is whether the end customer requires the tachograph on the platform or not.

Recommended hardware

• Tractor units and heavy rigids: FMC650 with J1939 + tachograph reading + RS485 for LLS.
• Large vans and heavy delivery vehicles without tachograph: FMC150 with native CAN.
• Construction machinery moving in and out of the depot: see GPS for construction.
• Trailers without continuous power: TAT240 with internal battery.

For all of the above, management via FOTA Web is included.

Frequently asked questions