Fuel level sensors + CAN bus: the complete fuel picture
The CAN bus knows what the engine burns. The sensor knows what the tank holds. On its own, each one has a blind spot. Together, they tell the whole diesel story, from the pump to the exhaust.
What is a fuel level sensor + CAN bus solution?
A fuel level sensor + CAN bus solution combines two measurements on the same vehicle. The capacitive sensor, also called an electronic fuel gauge, fitted inside the tank and calibrated in steps, measures the actual diesel level to within ±1 to 2%. The CAN bus reading, taken by the GPS tracker on the vehicle network, reports the liters injected by the engine, engine speed and the ECU mileage. The Tracky platform compares the two continuously. When the tank loses fuel the engine did not burn, it is theft: the alert goes out with the time, the volume and the GPS position. When the CAN bus confirms the consumption, the gap comes down to driving, routing or mechanics. This is the setup Tracky installs on heavy trucks in Morocco, with Teltonika FMC150 or Ruptela FM-Pro4 trackers.
Why is diesel, 30 to 40% of your costs, so hard to see into?
Between the pump and the billed kilometer, fuel passes through hands, routes and habits that nobody sees. Unless you measure it, on both ends.
Siphoning
10 to 20 liters a night, in a parking lot. Invisible on a monthly invoice.
Fake fill-ups
80 liters billed, 60 poured. Impossible to catch without onboard measurement.
Detours and idling
Kilometers that earn nothing, an engine running while parked.
Driving
A 4 L/100 km gap between two drivers on the same route. Nobody knows why.
What do the CAN bus and the fuel sensor each measure?
The CAN bus: what the engine burns
- Liters injected: the manufacturer's fuel consumption figure
- Engine speed, load, fault codes
- Actual mileage from the ECU
- No drilling: read directly from the vehicle network
Blind spot: it can't see the tank. Siphoning at night, a fake fill-up: nothing.
The capacitive sensor: what the tank holds
- Actual fuel level, continuously, ±1 to 2% after calibration
- Exact volume of every fill-up
- Drops while parked, time-stamped and geolocated
- Calibrated step by step on each tank
Blind spot: it doesn't know why the level drops: driving, a detour and a mechanical issue all look the same.
Why cross-check the fuel sensor with the CAN bus?
The tank lost 35 liters. Did the engine burn them? That's the only question that matters, and only cross-checking both measurements can answer it.
CAN: yes → driving or mechanical
The engine used those liters. It's a driver, route or workshop issue: driver score, trip replay, maintenance. A conversation, not an accusation.
CAN: no → fuel theft
The tank lost what the engine didn't burn. It's a security issue: real-time alert with the time, volume and GPS position. Proof, not suspicion.
Verified fill-ups: the volume measured by the sensor is compared with the pump receipt. Discrepancies stand out on their own.
Vehicle health: a lasting gap between actual consumption (sensor) and manufacturer consumption (CAN) points to tires, a filter, or a tampered meter.
Sensor only, CAN only, or both: which should you choose?
| Capability | CAN only | Sensor only | Sensor + CAN |
|---|---|---|---|
| Actual tank level | ✕ | ✓ | ✓ |
| Siphoning detection | ✕ | ✓ | ✓ |
| Exact fill-up volume (vs. pump receipt) | ✕ | ✓ | ✓ |
| Manufacturer consumption (liters injected) | ✓ | ✕ | ✓ |
| Engine speed, load and fault codes | ✓ | ✕ | ✓ |
| ECU mileage | ✓ | ✕ | ✓ |
| Driving or theft: settle it | ✕ | ~ | ✓ |
| Mechanical or meter discrepancy detected | ~ | ~ | ✓ |
| Evidence that holds up (time, volume, position) | ✕ | ✓ | ✓ |
✓ covered · ~ partial · ✕ blind spot
Three events, three verdicts
02:14, depot parking lot: level down 35 L with the engine off, CAN: 0 L injected.
Siphoning alert
A sudden drop while parked, not a single liter burned. That's fuel theft: instant alert with the time, volume and position. Time-stamped proof, and a lasting deterrent.
Casablanca to Marrakech run: sensor 41 L used, CAN 41 L injected, +3 L/100 km.
Overconsumption confirmed
The engine really did burn the extra fuel. The replay shows a detour and 40 minutes of idling with the AC on: a conversation backed by numbers with the driver, not a blind accusation.
Truck no. 14, 3 weeks: sensor 34.1 L/100 km, CAN 31.6 L/100 km, steady gap.
Lasting sensor vs. CAN gap
The two measurements differ consistently: not a one-off theft, not driving. A clogged filter, underinflated tires or a meter that no longer tells the truth. Time for the workshop.
The complete solution, installed and calibrated
- Device: Teltonika FMC150 / Ruptela FM-Pro4 — native CAN reading, 4G, sensor inputs.
- Sensor: capacitive, cut to fit the tank, calibrated step by step, with a level-to-liters table unique to each vehicle.
- Platform: automatic cross-checking, real-time alerts, fill-up reconciliation, reports every Monday. Data hosted in Morocco.
less fuel from the first year, with sensors and platform combined.
recovered in six months by a refrigerated fleet in Fez, from fuel theft alone.
measurement accuracy after step-by-step calibration, versus 10 to 15% for the factory gauge.
Frequently asked questions about fuel sensors and the CAN bus
What is the difference between a fuel level sensor and a CAN bus reading?
The CAN bus measures what the engine consumes: liters injected, engine speed, ECU mileage. The sensor measures what the tank holds: actual level, refuel volumes, drops while parked. Each has a blind spot. Only cross-checking the two tells you whether missing liters were burned by the engine or taken from the tank.
Is a GPS fuel gauge the same thing as a fuel level sensor?
Yes, in everyday use: what people call a GPS fuel gauge or electronic fuel gauge is a level sensor connected to the GPS tracker. It should not be confused with the original dashboard gauge, which is designed for the driver and only accurate to within 10 to 15%. A calibrated sensor measures to within ±1 to 2% and can detect siphoning.
Is the CAN bus enough to detect fuel theft?
No. The CAN bus cannot see the tank: siphoning at night with the engine off, or a fake refuel, leaves no trace in it. Detecting theft takes a level sensor inside the tank. The CAN bus then confirms that the engine did not consume the missing liters.
How accurate is a calibrated fuel level sensor?
After step calibration, a capacitive sensor measures the level to within ±1 to 2% of the volume, compared with 10 to 15% for the vehicle’s original gauge. Calibration builds a level-to-liters table specific to each tank, which keeps the reading reliable even on irregularly shaped tanks.
Which GPS trackers read both the CAN bus and a fuel sensor?
Tracky installs Teltonika FMC150 and Ruptela FM-Pro4 trackers: native CAN reading, 4G connectivity and dedicated sensor inputs. One tracker per vehicle is enough to send both measurements to the platform.
Can we test the solution before equipping the whole fleet?
Yes. Tracky installs the solution on one of your vehicles for 15 days, with no commitment. You compare the level curve with your pump receipts and decide on your own numbers.
See sensor + CAN cross-checking on your own truck
15-day trial on one of your vehicles: you compare the level curve with your pump receipts, and decide based on your own numbers.