Short answer
A badly installed GPS tracker keeps sending data, so nothing looks broken. But the data is corrupt: positions jump under metal roofing, engine hours accumulate from an unstable power source, and decisions get made from numbers no one has reason to doubt until the pattern is already expensive.
Key takeaways
- A corrupt installation does not fail loudly, the device keeps transmitting, which is what makes the mistake expensive.
- Mounting under metal, or near a metallised windscreen, blocks the GNSS signal the tracker depends on.
- An unstable power source produces phantom engine-hours and dropped records, not an obvious fault.
- Ignition wired to the wrong circuit (an ACC wire) reports the vehicle as off when it is not.
- A short pre-handover acceptance test catches all of this before the vehicle goes back into service.
01Why installation decides data quality
The most common field mistake is not a wiring error that stops the device from working. It is a rushed installation that leaves the device working, but reporting numbers that are quietly wrong. A tracker mounted under a metal roof or powered from an unreliable source does not go silent, it keeps sending positions, speeds and engine-hours records on schedule, which is exactly why the mistake goes unnoticed. Nothing in a fleet dashboard flags a device as "installed badly." It only shows positions that jump, hours that accumulate strangely, or trip data that does not match what a driver reports. By the time anyone investigates, weeks of decisions may already rest on the corrupted numbers, and the installer who did the rushed job is long gone from the vehicle.
02Mounting under metal: what it does to GNSS
Teltonika's own installation guidance is explicit on this point: avoid placing the GNSS antenna under metal surfaces, and where an external antenna is used, mount it as close to the windshield as possible rather than under the metal roofline, because a metallised or heavily tinted windscreen attenuates the same signal a metal roof blocks outright. The antenna also has a maximum tolerated lean of about 30 degrees before it counts as incorrectly mounted, and its sticker side must face down. None of these are cosmetic details. GPS operates on the L1 frequency of 1575.42 MHz, a signal weak enough that a few centimetres of steel between the antenna and the sky is often enough to turn a precise fix into an intermittent one, which is what produces the jumping positions a fleet manager eventually notices and cannot explain.
03Power: the unstable-source failure and phantom engine hours
Teltonika's wiring guidance also warns that power drawn from the wrong point can drop five to thirty minutes after the vehicle's own computer falls asleep, which is why the manual instructs installers to measure voltage again after connecting, not just before. It further requires the ground wire to go to a designated low-impedance point, stating plainly that an arbitrary chassis ground can cause unstable operation or outright device failure. An unstable power source does not just cause dropouts. If ignition or movement detection is being derived incorrectly as a side effect, the device can log engine hours or trips that never happened, or fail to log ones that did, corrupting exactly the counters a maintenance schedule or a payroll calculation might depend on.
04Ignition sensed from the wrong circuit
A specific and common wiring mistake is connecting the ignition input to an accessory (ACC) circuit rather than genuine ignition. Teltonika's own verification test names this directly: the correct wire must not lose power while the engine is starting, and it must not be an ACC wire. An ACC circuit stays powered for accessories like the radio even when the engine is off, so a device wired to it reports the vehicle as "on" during periods it is actually parked and idle, inflating engine hours, misreporting trips, and undermining any idling or driver-behaviour analysis built on ignition status, since those features depend on exactly this signal to know when a vehicle is actually running rather than merely switched to accessory mode.
05Heat: cabin temperature versus the device's rated range
A parked vehicle cabin in Gulf summer regularly exceeds ambient air temperature by a wide margin, which matters because device operating ranges are not uniform. A Teltonika FMC920 is rated to operate from −40 to +85 °C, but its internal Li-ion backup battery carries its own, much narrower limits: it will only charge between 0 and +45 °C, and only discharge between −20 and +60 °C. An installer who mounts the device in direct sun behind a dashboard, without accounting for the battery's separate limits, risks the battery refusing to charge correctly or the device throttling itself in ways that show up later as gaps in the data rather than as an installation complaint at the time of fitting, when the underlying cause is far harder to trace back.
06What corrupt data looks like downstream
The consequence is exactly what the owner's view describes: the device keeps transmitting, but the numbers are corrupt, positions that jump, and phantom engine hours. A fleet may make thousands of riyals in decisions based on wrong data, and field a driver's complaint that turns out to be baseless, all because of how carelessly the installation timing and method were handled. A maintenance schedule built on inflated engine hours triggers early, unnecessary service. A driver disputing an idling alert may be entirely correct if the ignition source was miswired. And a position that jumped under a metal canopy can read as a route deviation that never happened. None of this looks like a technical fault; it looks like normal fleet data, which is what makes it costly.
07A pre-handover acceptance test, and how ENTEK.AI treats installation
A short test before a vehicle returns to service catches nearly all of this. Confirm both status and navigation LEDs blink as expected, drive far enough to get a stable GNSS fix away from covered parking, verify ignition status changes correctly when the engine starts and stops without lag, and re-check power voltage after the vehicle has sat idle for thirty minutes to catch the sleep-mode power drop Teltonika's own manual warns about. ENTEK.AI treats installation as a data-quality control point, not a logistics afterthought, because every downstream feature, idling alerts, engine-hours maintenance triggers, driver-behaviour scoring, inherits whatever the installation got wrong. A device that reports on schedule is not proof of a good installation; only a deliberate check against a real drive is.
| Mistake | How it looks in the field | What it corrupts |
|---|---|---|
| Antenna mounted under metal | Device works normally, GNSS fix intermittent | Positions jump; route and geofence accuracy |
| Power from an unstable source | Sleep-mode drops, no obvious fault reported | Records dropped; downstream trip and hours data |
| Ignition wired to ACC circuit | Vehicle reports as "on" while parked | Engine hours, idling alerts, driver-behaviour scoring |
| Device in direct heat behind dashboard | No fault at install time | Battery charging, data gaps appearing weeks later |
| No acceptance test before handover | Nothing flags the installation as bad | Every feature that depends on the data above |
Figures and sources
- Teltonika official guidance, GNSS antenna and metal surfaces: avoid mounting the GNSS antenna under metal surfaces (Source: Teltonika Telematics Wiki, Mounting recommendations, as of 2026-08-31)
- Teltonika maximum GNSS antenna tilt before mounting is considered incorrect: more than 30 degrees of lean (Source: Teltonika Telematics Wiki, Mounting recommendations, as of 2026-08-31)
- GPS L1 carrier frequency: 1575.42 MHz (Source: GPS Interface Specification (official), as of 2026-08-31)
- Teltonika external antenna placement guidance relative to metal roofline: as close to the windshield as possible (Source: Teltonika Telematics Wiki, Mounting recommendations, as of 2026-08-31)
- Teltonika warning that power on the chosen wire may disappear after the vehicle computer sleeps: power may drop 5 to 30 minutes after sleep; re-measure after connecting (Source: Teltonika Telematics Wiki, Mounting recommendations, as of 2026-08-31)
- Teltonika ground-wire requirement, and the stated consequence of an arbitrary ground point: must use a designated low-impedance point; arbitrary chassis ground can cause instability or failure (Source: Teltonika Telematics Wiki, Mounting recommendations, as of 2026-08-31)
- Teltonika ignition-wire verification test: power must not disappear during engine start; wire must not be an ACC wire (Source: Teltonika Telematics Wiki, Mounting recommendations, as of 2026-08-31)
- Teltonika FMC920 operating temperature (device), and its Li-ion backup battery charge/discharge limits: device: −40 to +85 °C; battery charge 0 to +45 °C; battery discharge −20 to +60 °C (Source: Teltonika Telematics Wiki, FMC003/FMC920 General description, as of 2026-08-31)
- Teltonika Li-ion backup battery charge-temperature limit: 0 to +45 °C (Source: Teltonika Telematics Wiki, FMC920 General description, as of 2026-08-31)
- Teltonika movement-source GNSS speed threshold for MOVING vs STOP: ≥5 km/h = MOVING; <5 km/h = STOP (Source: Teltonika Telematics Wiki, System settings (Movement Source), as of 2026-08-31)
- IEC 60529 IP code, meaning of the first and second numerals: first: protection against solid objects; second: protection against water ingress (Source: IEC 60529, Degrees of protection provided by enclosures (IP Code), as of 2026-08-31)
- SAE J1939 CAN bus termination requirement: 120 ohm resistor at each end of the backbone (Source: SAE J1939-11, Physical Layer, as of 2026-08-31)
- Teltonika install-verification step for confirming correct installation: both Status and Navigate LEDs should blink as expected (Source: Teltonika Telematics Wiki, Mounting recommendations, as of 2026-08-31)
Questions
Why does a badly installed tracker not show an obvious fault?
Because it keeps transmitting data on schedule. The problem is not that the device stops working, it is that positions, engine hours or trip data are quietly wrong, and nothing in a standard dashboard flags "installed badly" as a fault state.
Why does mounting near metal matter so much?
GPS operates on a weak L1 signal at 1575.42 MHz. A few centimetres of metal roofing, or a metallised windscreen, is often enough to turn a precise position fix into an intermittent one, which is what produces jumping positions on a fleet map.
What is the single most useful check before a vehicle goes back into service?
Re-check power voltage after the vehicle has sat idle for about thirty minutes. Teltonika's own documentation warns power can drop after the vehicle computer sleeps, and this single check catches the most common silent power-wiring mistake.