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Fleetwatch FMS · Email Alerts
Low Fuel Alerts: How They’re Triggered
A low fuel alert is an email Fleetwatch sends when a vehicle receives noticeably less fuel than expected for the miles it has run. It can flag a bus that wasn’t fully fueled before it heads back out, helping to prevent a road call. This article explains every condition that must be met for an alert to go out, and how to tune the settings.
Where the Settings Are
In Data Tools, open the vehicle and go to:
Vehicles › Settings › Properties tab › Fuel And Fluid › Fuel
| Setting | Example value | Role in low fuel alerts |
|---|---|---|
| Enable Low Fuel Alerts | Checked | Must be on for the vehicle to send alerts (rule 1) |
| Max Trip Distance Without Fuel Bounding | 400 miles | Miles run must be within this limit (rule 4) |
| Percentage Expected To Trigger Low Fuel Alert | 70% | How short of expected the fueling must be (rule 6) |
| Fluid Alert Threshold | 20% | How much of the tank the missing fuel must represent (rule 7) |
| Send No-Fuel Alerts | Unchecked | Allows alerts when no fuel was dispensed (rule 8) |
The Rules: All Must Be True
A low fuel alert is sent only when every one of these conditions is met. If any one fails, no alert is sent.
The vehicle and the lane
| 1 | Low fuel alerts are enabled for the vehicle. Enable Low Fuel Alerts must be checked. It’s on by default. Database field: Vehicles.VehicleTriggerLowFuelAlerts |
| 2 | It’s a real vehicle. Containers, test numbers, and unknown vehicles (vehicle 0) never trigger alerts. |
| 5 | It was fueled at a service lane. Only service lanes can trigger alerts. Maintenance bays and similar controllers cannot. |
The miles run
| 3 | At least 40 miles since the last fueling. Short trips use too little fuel to judge reliably. |
| 4 | Within the Max Trip Distance. The raw miles run must be within the Max Trip Distance Without Fuel Bounding limit (typically 400 miles). Higher mileage usually points to a missed fueling or a bad odometer reading, not a real trip. |
| 9 | A valid odometer reading. The transaction must include an odometer input, and Fleetwatch must consider it valid. |
The fuel dispensed
| 6 | Less than the trigger percentage of expected. The fuel dispensed must be less than the expected amount × Percentage Expected To Trigger Low Fuel Alert. See the examples below. Database field: Vehicles.VehicleLowFuelTrigger |
| 7 | The shortfall is a big enough share of the tank. The “missing” fuel (expected minus dispensed) must be at least the Fluid Alert Threshold percentage of the tank capacity (default 20%). This keeps small shortfalls on large tanks from triggering alerts. |
| 8 | Fuel was dispensed, and the expected amount fits the tank. Some fuel must have been dispensed, and the expected amount must be within the tank’s capacity. The exception: if Send No-Fuel Alerts is checked, the vehicle can also trigger an alert when no fuel was dispensed. |
Choosing the Trigger Percentage (Rule 6)
A higher percentage sends more alerts, and a lower percentage sends fewer. For a vehicle expected to take 60 gallons:
| Trigger | Pump at least this to avoid an alert | When to use it |
|---|---|---|
| 90% Most alerts |
54 gal 60 × 0.90 = 54 |
When even 6 gallons short would be critical to avoiding a road call. |
| 70% Fewer alerts |
42 gal 60 × 0.70 = 42 |
When 10–20 more gallons would be needed to bring the bus back to the yard. |
| 50% Fewest alerts |
30 gal 60 × 0.50 = 30 |
When operations only wants to know if a bus got about half the fuel it should have. |
The Tank Threshold (Rule 7)
Example: a bus with a 125-gallon tank was expected to take 78 gallons, but only 46 gallons were dispensed.
| Missing fuel | 78 − 46 = 32 gal |
| Share of the tank | 32 ÷ 125 = 25.6% |
| Compared to the 20% threshold | 25.6% is greater than 20%, so the shortfall is significant |
Rule 7 passes. If the other rules pass too, an alert is sent.
Putting It Together
Same bus: 125-gallon tank, 78 gallons expected, trigger set to 70%, tank threshold 20%, and a valid odometer showing 250 miles since its last service-lane fueling.
| Dispensed | Rule 6 (below 70% of 78 = 54.6 gal?) | Rule 7 (shortfall ≥ 20% of tank = 25 gal?) | Alert? |
|---|---|---|---|
| 46 gal | Yes, 46 < 54.6 | Yes, 32 gal short | Alert |
| 52 gal | Yes, 52 < 54.6 | Yes, 26 gal short | Alert |
| 54 gal | Yes, 54 < 54.6 | No, only 24 gal short | No alert |
| 60 gal | No, 60 ≥ 54.6 | — | No alert |
Tuning Tips
|
Too many alerts?
• Lower the trigger percentage (for example, 90% to 70%).
• Raise the Fluid Alert Threshold so only larger shortfalls count.
• Check that the vehicle’s MPG values are realistic, since they drive the expected amount.
|
Not getting alerts?
• Confirm Enable Low Fuel Alerts is checked.
• Check that the vehicle is fueled at a service lane, not a maintenance bay.
• Check that odometer readings are coming in and are valid, and that trips are between 40 miles and the Max Trip Distance.
|
Questions about low fuel alerts? Contact Fleetwatch Support.