Automower 'no loop signal' on wire models

For the nine causes Husqvarna's manual gives for no loop signal, and what it says to do, see the 420, 430X, 440 and 450X page.

What the reports have in common

About a dozen owners are behind the reports below, mostly on the 310 (bought between 2015 and 2022) and the 315, with a 315X and a 430X NERA in the French threads.

• The station light often stays green. Several 310 owners had a steady green station light, no eco mode, and a loop signal that regenerated without trouble, yet the mower kept saying no loop signal, sometimes for days at a time and then starting normally¹.
• It can come and go with the weather. Two owners saw it work while the ground was damp and fail when it dried or the sun warmed the soil¹.
• Re-plugging sometimes cured it for a day. One owner pulled the loop wire off at the station and re-plugged it, and it worked until the next morning. Another found that taking the mower out of the station and starting it by hand worked¹.

What fixed it, by number of owners

Damaged cable or a break, found and repaired: three owners. One 310 owner's cable was kinked and its sleeve broken in two places; after the repair the mower ran again, though he adds that the next mower will be a wire-free one¹. A 2015 310's cable was damaged and oxidised around a bush; renewing it brought the station light back to steady green¹. A third found a fault in the last few metres of cable before the station, after first suspecting a joint, and re-laid that piece instead of digging it out¹.

A loose underground joint, together with a new front sensor: one owner. A 310 bought in 2022 kept failing to start on schedule, and a dealer's sensor swap alone only got it to start about one time in five. The fix was a new loop sensor plus a new underground connector (two hours of work and material, 170 euros). The owner suspects the sensor was not needed, because the joint worked loose and failed mainly when the sun heated the ground¹.

Joints replaced without a lasting result: two owners. A 310 owner replaced an underground joint, saw the mower start on schedule the next morning, and had the error back after rain¹. Another found part of a long loop had been joined with clamps, cut out that stretch and replaced both clamps; the resistance fell to 2.5 ohm, the fault returned two days later, and the owner is selling the mower².

A new front loop sensor: two owners. One 310 owner ordered the module, fitted it himself and the mower ran (a dealer had meanwhile failed to get the part in three weeks)¹. A French 310 owner whose mower left the work area after an hour changed the front loop-signal board and ran four hours without trouble⁵.

A new station board: five owners helped, two not.

• A 310 owner who had had the error for about a year, through a new boundary cable and a replaced joint, fitted a new board in the station and, three weeks later, reported it still ran¹.
• A 315 owner's board had died: the light blinked blue even with the loop bridged. A new board brought a steady green light⁴.
• A French 315X owner whose station light had gone out replaced the board and the mower ran again⁶.
• A French 310 owner found the station light off and the mower saying no loop signal, with 28 V at the station's contacts. A new board, fitted in ten minutes, fixed it⁷.
• A French 430X owner's mower stopped 30 cm after leaving the station. The loop's resistances were fine, a test loop of spare wire worked, and the station light stayed steady green when the loop was unplugged. A new station board fixed it⁸.
• Against that, a 310 owner's technician replaced the board and the transformer without effect, and the fault turned out to be a joint and the sensor¹. Another 310 owner's board swap gave a few days and the fault returned; a cracked cable was found¹.

After any station-board swap, make a new loop signal: three threads. A 310 owner's closing tip, once the new board was in, was to make a new loop signal and check the clock⁷. Forum regulars in two threads say the same: a mower does not recognise the signal of a new board unless a new loop signal is made with the mower in the station, and without it behaves as if there were none¹⁰⁹. In one of them the new board was fitted and the new signal still could not be made, which the regular took to mean a second fault⁹.

Storms: two owners, one regular. The 430X owner above had had a thunderstorm shortly before the fault, and neighbours' gate motors and a meter had burnt out⁸. A 315X owner's old board was brown where it had burnt, and the owner says they will be more careful in storms⁹. A regular writes that station boards "often" fail after a lightning strike⁸, and another says the only protection he sees is to unplug everything from the station in a storm; he fitted a surge-protected socket for the transformer and is not convinced it helps⁹.

Crossed cables under the station: one owner. A 315's board was replaced and the mower then refused to leave the station with "no loop signal". The owner removed a crossing of two cables under the station and the fault went away. His lesson: the cables must not touch, run close together or cross there⁴.

When none of that was it

• The mower itself. A 310 lost every loop sensor reading, 100 to 0, about 5 m (16 ft) from any wire, even on a brand-new test loop. The station board and power supply were not the cause. When he took the mower apart he found a chip on the main board that had lost a leg, and soon afterwards the mower stopped working altogether³.
• The mower's main board, after the station board was replaced. The 315X owner above fitted a new station board and a new transformer (27.4 V at the cable), got a steady green light, and still read zero on every loop signal, with no new loop signal possible. A repairer found the mower's own main board defective and quoted about 550 euros. The owner bought a 305 for a smaller garden instead⁹.
• The transformer, after the station board was replaced. A 430X owner who had also changed the transformer and the battery could not get the mower to move: the light was red, and green only with the mower in the station, and a new loop signal failed. A service centre said the transformer was at fault, fitted its own, and says the mower then worked¹⁰.
• Still unresolved. One owner wrote that his dealer could not fix it¹. The 310 whose loop read 7.5 kilo-ohm on one side had the fault return two days after the repair².

How owners narrowed it down

These are owner and forum practice, not Husqvarna instructions.

• Bridge the loop at the station. Disconnect the loop and bridge the terminals with a short wire. A green light means the board works². In the 315 thread the light stayed blue with the loop bridged, which is how that owner knew the board was dead⁴.
• Build a test loop of spare cable. One owner's mower ran at once on a direct connection, which sent him looking in the buried wire¹. Another's mower failed on a new test loop in the same way, which pointed at the mower³.
• Do not trust a resistance reading on its own. One owner measured 5 ohm on all legs, wet or dry, and still had the fault¹. Another measured 7.5 kilo-ohm on one side and 2.5 ohm on the other².
• Finding a break. Forum members suggest a medium-wave radio held over the cable, an electric-fence energiser, or stabbing a pin through the sheath at the middle of the loop and halving the section. The radio found two doubtful spots for one owner; a pin test is described in the same thread as another way¹². One forum member suggested burning through the break with a car battery; another pointed out the arithmetic: at that resistance it cannot work².
• A blue flashing light is not always the board. A forum member says a blinking blue light means the station board is defective. Owners in these threads found a cable or joint fault behind it more often than a board¹²⁶.

What's unknown

• No single cause. Cable, joints, the front sensor, the station board and the mower's own board all appear.
• Firmware. None of these reports gives a firmware cause for the wire models. Owners did not state versions.
• How common it is. These are the cases owners posted. They are not a count of Automowers affected.
• Which model each fix applies to. Most reports are the 310; the 315, 315X and 430X NERA appear once or twice each.