CAN bus or fuel level measurement: which fuel consumption measurement is accurate?
In short
Fuel level measurement (a probe) calculates consumption from the level in the tank — the sensor may be accurate, but the conversion depends on the shape of the tank, the level shifts on a slope, and in principle it cannot detect fuel theft from the return line at all. CAN bus injector measurement queries the engine control unit for the fuel actually injected, with an error of ~1% depending on the vehicle — independently of the tank geometry.
Why does level measurement get it wrong — even when the sensor is good?
The level is not litres. Consumption has to be converted from the change in level into litres based on the geometry of the tank. With a regular, box-shaped truck tank this is still acceptable; with an irregularly shaped tank (passenger car, van, machinery), the same number of centimetres means a different number of litres at the bottom, middle and top of the tank.
The level moves. Slopes, bends, braking, thermal expansion and sloshing distort the instantaneous value — which is why level-based systems typically only reliably flag larger discrepancies.
It cannot see the return line. In diesel engines, part of the fuel delivered to the injectors flows back into the tank through the return (leak-off) line. If this line is tapped, the tank level falls at exactly the “normal” rate — the theft is invisible to level measurement.
Finally: the probe can be physically tampered with, and installing it means intervening in the tank.
What does the CAN injector method measure instead?
The factual data of the engine control unit: exactly the amount of fuel the injector has injected. This is independent of the shape of the tank, the slope and the return line; compared with the quantity refuelled (from fuel card invoices), any discrepancy — theft, technical fault, driving style — can be detected immediately. FleetControl uses CAN-based measurement exclusively; we do not install probes.
Frequently asked questions
Does CAN measurement work in every vehicle?
On vehicles equipped with a CAN bus — modern passenger cars, vans, buses and trucks typically are. For older vehicles without CAN, settlement based on the quantity refuelled (fuel log) can be used.
Can theft from the return line be detected?
Yes: the discrepancy emerges from a longer-term comparison of the quantity injected (measured) and the quantity refuelled — with level measurement, this is not possible even in principle.