Robot Mower Lost Its Place: Signal, Loop & Positioning Failures, Diagnosed in Order
Disclosure: Some parts links in this article are affiliate links; we may earn a commission at no extra cost to you (see footer). Fixes are drawn from manufacturer manuals, fault tables, and documented owner failure patterns.
Safety first, every time: Power the mower OFF and isolate the battery before handling blades, clearing the cutting deck, or working on the underside. When tracing a live boundary wire, you are listening only — no digging near a wire until its route is confirmed, and call your utility locate service before any digging beyond shallow turf work. If a power supply trips a GFCI repeatedly, stop: that is service territory, not a reset loop.
Positioning failure is the robotic mower's #1 stop-work fault family — across both navigation generations. Wired owners get "no loop signal." Wire-free owners get weak-GPS stalls and "antenna moved" errors. Different radios, same owner experience: a mower sitting in the grass, blinking, going nowhere. The diagnostic discipline is also the same: read what the machine is actually claiming before you touch anything, because each symptom below is the machine narrowing the fault down for you.
Step 0: Read the station (and the light) first
On a wired system, the charging station's LED is the single most informative component in the yard — Gardena's entire support flow is built around station LED colours, and Husqvarna's manual fault table leads with loop-signal states. On wire-free systems, the mower's light and app messages play the same role. Decode before diagnosing:
| What it says | What it is actually claiming | Go to |
|---|---|---|
| Station LED flashing blue (Automower pattern), mower reports "No loop signal" (incl. error E02) | The loop circuit is open or unreadable: station power, a broken boundary wire, a bad coupler, or a wire routed wrongly around an island | Wired path, checks 1–5 |
| Station LED off entirely | No power at the station, or a dead power supply — the loop has nothing to carry | Wired path, check 1 |
| Flashing yellow light (Navimow pattern) | Weak GPS/RTK signal at the mower's position — Navimow's own support base documents this state and sells the fix | RTK path, checks 1–3 |
| App: "charging station or antenna was moved" | The reference point the map was built against no longer matches. Something physical moved — or the station settled, got knocked, or was "tidied" | RTK path, check 4 |
| App position and real position disagree; mower mows a ghost offset | Multipath drift or a corrupted map — the fix is positional hygiene or a remap, not parts | RTK path, check 5 · Vision path |
| Mower can't find the station / docks but won't charge | A search, guide-signal, contact, or power-delivery fault — see the docking section below | Docking & charging |
The wired path: "no loop signal" and wire breaks
| # | Cause | Check | Fix |
|---|---|---|---|
| 1 | Station power — including the idle-voltage trap | A failing switch-mode supply can read ~28V at idle on a meter and collapse the moment the station draws charge load ("hiccup mode"). A good voltage reading does not clear the supply. Swap in a known-good supply, or test under load, before condemning anything else | Replace the supply if it's the fault (~$100–200 class part) [AFFILIATE LINK: robot mower power supply]. Confirm the outlet/GFCI first — it's free |
| 2 | Terminal corrosion at the station | Boundary and guide-wire terminals oxidise outdoors; a green/white crust at the connector is resistance the loop signal can't afford | Power off, clean terminals, re-seat connectors. Protect the joint when you close it up |
| 3 | Broken boundary wire — aerators, edging tools, rodents, roots, freeze-thaw | Triage by where the error occurs. If the mower reports the fault docked at the station, suspect the station side (power, terminals, couplers near the dock). If it mows part of the lawn and fails in a zone, the break is on that side of the loop. Then find it (next section) | Cut out the damaged section, splice with waterproof gel-filled couplers — never twisted bare wire and tape, which corrodes into next spring's repeat fault [AFFILIATE LINK: boundary wire couplers] |
| 4 | A failed coupler from a previous repair | Every old splice is a suspect. Couplers that weren't fully crimped or gel-sealed fail seasonally with moisture and frost heave | Re-make suspect joints properly. Keep a mental (or written) map of every splice in your loop |
| 5 | Wire routed wrongly around an island, or signal interference | Manuals list both: a loop crossed at an island cancels its own signal, and metal objects or buried cables near the wire distort it | Re-check island routing against the manual's diagram; re-route sections that pass over buried utilities or along metal edging |
Finding the break: the AM-radio trace and friends
- Halve the loop. If your station and mower allow a temporary test loop (a short spare-wire loop at the station), confirm the station itself generates signal first — this separates "station fault" from "wire fault" in five minutes. [AFFILIATE LINK: boundary wire roll]
- The AM-radio method. The loop signal radiates a tone a portable AM radio can hear. Tune to an empty AM frequency, hold the radio low over the wire's route, and walk the loop: a healthy wire gives a strong, steady tone; the tone fades or dies at the break. It is the field method dealers use, and it costs nothing.
- Work the likely suspects first. Breaks cluster where the world touches the wire: aeration zones, edging lines, gate paths, root heaves, and last year's repair joints (check 4).
- Repair once, properly. Gel-filled waterproof couplers, slack in the splice, and the joint buried at the same depth as the run. A break repaired badly is a break scheduled.
The RTK path: weak fix, moved antenna, drifting position
| # | Cause | Check | Fix |
|---|---|---|---|
| 1 | Sky view at the antenna | The reference antenna needs open sky. Antennas sited under eaves, against a tall wall, or under canopy start marginal and fail as trees leaf out — which is why "it worked in April" is a classic June complaint | Re-site the antenna to the most open sky available; follow the brand's siting rules (clear horizon, distance from walls and metal roofs) |
| 2 | Sky view at the mower | Flashing-yellow weak-signal states concentrate where the mower works: under canopy, in narrow side passages between houses, against walls (multipath reflections corrupt the fix) | If one zone always fails, that zone is the diagnosis. Options: a signal-enhancement antenna (Navimow sells one for exactly this), re-zoning the problem strip to a different treatment, or accepting that this yard section is a wire/LiDAR section (see check 6) |
| 3 | Signal-enhancement antenna: fix vs. accessory | It raises the reference signal where geometry is marginal. It does not create sky where a roof or a mature oak occupies it | Buy it when the failure is intermittent and marginal [AFFILIATE LINK: Navimow signal enhancement antenna]. Don't buy it to fight a canopy — that's a navigation-family problem |
| 4 | "Antenna/station was moved" after physical disturbance | The station got bumped, the antenna pole was straightened, the dock was lifted for edging. The map is anchored to where things were | Use the app's relocation flow, then remap if the app demands it. Then make the station immovable: anchored dock, antenna pole that isn't a leaning post |
| 5 | Multipath drift near walls and metal | Position wanders or the mower mows a consistent offset near reflective surfaces; fences and metal sheds are repeat offenders | Confirm the offset is positional (mower's reported vs. actual position), improve antenna siting, and remap the affected zone. Persistent drift in a walled courtyard is a siting limit, not a defect |
| 6 | The yard is a LiDAR yard | If checks 1–5 describe your whole lawn — mature canopy, enclosed passages, walls everywhere — the machine isn't broken. The navigation family is wrong for the property | This is a buying answer, not a repair: fusion/LiDAR models (see the buying guide's treed-lot recommendation) or a wired system that ignores sky entirely |
The vision / LiDAR path: drift, darkness, dirty eyes
- Dirty sensors: grass sap, dust film, and morning dew on a lens or LiDAR window degrade positioning before they stop it. Clean with a soft cloth per the manual; make it part of the weekly round (see maintenance).
- Low light: camera-led systems lose their references at dawn, dusk, and under heavy shade. If failures are time-of-day patterned, schedule mowing in full light before replacing anything.
- Featureless lawns: a large, uniform, freshly-seeded or dormant lawn gives vision systems nothing to triangulate on. Drift on an empty canvas is a known failure shape, not damage.
- Map corruption: a map built in poor conditions encodes the errors. Remap in good light, clean sensors, at walking discipline — a careful remap fixes more "possessed mower" reports than any part.
Docking & charging faults
| # | Cause | Check / Fix |
|---|---|---|
| 1 | Can't find the station (wired) | Guide-wire/search settings first — the mower follows search behaviour you configure. A mower orbiting the lawn at low battery is often a settings or guide-wire signal problem, not a dead battery |
| 2 | Dead battery short of home | A pack at end of life fades mid-route. Runtime well under rated (see battery protocol) means budget the pack (~$150–$350 typical), not the mower |
| 3 | Docked but not charging | Oxidised charging contacts and slight dock misalignment are the top pair. Clean contacts on mower and dock, confirm the dock sits level and the mower's approach is unobstructed |
| 4 | The idle-voltage trap again | A supply that reads ~28V idle but collapses under charge load presents exactly as "docked, not charging." Test under load or swap before buying a battery [AFFILIATE LINK: robot mower power supply] |
Repair, warranty, or replace? The triage
- Under warranty (commonly 2 years on major brands): document the symptom — the LED state, the error code, where in the lawn it happens — run the manual's reset steps, then claim. Positioning faults diagnosed by location (Step 0's table) are the claims dealers resolve fastest.
- Out of warranty, fault is a part: power supplies (~$100–200), stations/docks ($100–300), batteries ($150–350) — repair, in that price order of suspicion, against a $999–$5,000 replacement.
- The 40% rule: if a repair quote exceeds ~40% of a current equivalent model, replace — and reconsider the navigation family while you do, because a yard that defeated one RTK machine will defeat the next.
- Dealer labour changes the math: Automower owners pay dealer rates but get wire-finding and re-trenching done by people with the tools. DTC owners pay in their own weekends. Neither is wrong; price your own time honestly.
This article is the free core. The Wire-Free Decision Guide ($39) is the buying-side companion: the navigation eliminator worked in full, so the "is my yard simply wrong for RTK?" question this page raises gets a complete answer — sky-view assessment, family-by-family fit, and the shortlist that follows. [CHECKOUT LINK: Decision Guide — Gumroad]
Prevent the sequel: the maintenance protocols — blades, batteries, storage — that keep the other failure families away. Storing the mower soon? The winter storage protocol. Still shopping? The buying guide compares the current field.