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Troubleshooting A "NO LOOP SIGNAL" Error On A Husqvarna Automower

A "No Loop Signal" error can be caused by several different components and issues and does not always mean that there is definitely a break in the boundary wire. In this guide we've tried to cover all of the possibilities in an easy to follow step by step format. But before getting started there a few things we need to inform you of. First, all of the maroon colored text that is underline are actually clickable links that will take you to pictures, videos, or products. The purpose for them is to provide more information for clarification or to make it easier to see what part is being referenced and the replacement options if needed. Secondly, this guide will continue to evolve! We will continue adding more pictures and information to continue to help make solving no loop errors easier for you to solve. Be sure to follow ALL instruction STEP BY STEP.


Ok, lets get into the troubleshooting. Follow this trouble shooting guide to help narrow down the cause of NO LOOP SIGNAL error. Start by verifying the color of the LED on your Automower's charging station and follow the steps listed for that section.


What color is the LED in your mower's charging station? Select (Click on) one of the following:


Sections for use after verifying charging station LED color and following steps listed for your charging stations indicated status:


A) Solid Green LED

A-1) Pair mower to charging station by creating new loop signal. Select your model here to see how to pair the mower to the charging station: 115H, 310, 315, 315X, 415X, 430X, 430XH, 435X, 450X, 450XH, 520, 520H, 535AWD, 550, 550H

A-2) If new loop signal was created but NO LOOP signal error remains, remove boundary wires from AL and AR terminals on the back of the charging station. If the LED is still solid green then the charging station board has failed and needs to be replaced.

A-3) If LED turns flashing blue with boundary wires removed from AL and AR terminals on charging station, test voltage output of charging station by measuring voltage between AL and AR terminals on back of charging station. If voltage is less than 25 volts DC, verify that there is 28 continuous DC volts coming into the charging station circuit board. If there is 28 continuous DC volts coming into the charging station board then the charging station circuit board is the issue and needs to be replaced.

A-4) If NO LOOP SIGNAL error occurs with solid green LED while the Automower is mowing, then move on to section I (No Loop Signal Error In Middle Of Work Area Or In Specific Part Of Work Area

B) Flashing Green LED (ECO Mode No Loop Error)

B-1) Flashing green LED indicates that ECO mode is active. To reset a NO LOOP SIGNAL error caused by ECO mode watch this VIDEO or follow these steps:

B-1A) Place mower in charging station

B-1B) In mower's settings turn off ECO mode

B-1C) Remove mower from charging station to verify that LED is now solid green.

B-1D) If LED is NOT solid green then repeat steps B-1A and B-1B. Before moving to step B-1C unplug the charging station transformer/power supply for 2-3 minutes to allow charging station to reset. Plug transformer/power supply back in to provide power to charging station. Remove the mower from charging station to verify that LED is solid Green.

B-2) If LED is still flashing green after following steps B-1A through B-1D then the charging station circuit board is the issue and needs to be replaced.


C) Solid Blue LED

A solid blue LED means there is an excessive amount of boundary wire (Over 800M) in your mower's boundary loop system. When over 800 meters of wire is used in the boundary loop the signal strength begins to weaken. To diagnose a no loop signal error with a solid blue LED:

C-2) Use a multi meter to measure the resistance between the 2 ends of the boundary wire.

C-3) If resistance is between 14 - 17 ohms check all wire connections and splices for corrosion or weak connection. Replace as necessary to lower resistance.

C-4) Remove any unnecessary sections of wire such as islands that are no longer needed and test resistance again or look for LED to turn solid green.

C-5) If mower continues to have a no loop error in the middle of the working area move on to section I (No Loop Signal Error In Middle Of Work Area Or In Specific Part Of Work Area

D) Flashing Blue LED

D-1) Remove boundary wires from AL and AR terminals on the back of charging station.

D-2) Use a multimeter to test resistance between the 2 ends of the boundary wire.

D-3) If resistance is over 17 ohms, or there is no continuity between the two ends of the boundary wire, then you have corrosion/rust in your boundary wire, a partial wire break, a break in the wire, bad connector or splice, or possibly multiple bad spots in your boundary loop. Move on to section K (Boundary Wire Break, Partial Break, Corrosion, & High Resistance)

D-4) If your resistance is 15 ohms or less, then your boundary loop is likely not causing the error. With the boundary wires still disconnected from the station, use a multimeter to see if/how much voltage is coming out of the charging station. Measure voltage between AL and AR terminals on the back of charging station.

D-5) If voltage is less than 25 volts DC between AL and AR terminals remove the front of the charging station to access the circuit board.

D-6) Disconnect the large charging station harness connector at the circuit board and measure voltage between the red wire and black wire in the connector. If you have 28 continuous volts DC then check the resistance of the charging station wiring harness from the circuit board connector through the boundary wire connections on the back of the charging station.

D-7) If charging station harness and/or terminals fail resistance test, replace the failed components.

D-8) If internal harness and terminals pass resistance testing then the charging station circuit board has failed and needs to be replaced.

D-9) If you have less than 28 volts DC between the red wire and black wire in the charging station circuit board plug, then unplug the low voltage cable from the transformer but leave the low voltage cable plugged into the charging station. Use a multimeter to measure resistance between the transformer end of the low voltage cable and the red wire and black wire in the charging station harness plug.

D-10) If resistance between the ends of either wire is above 1 ohm then test the low voltage cable and charging station harness separately to determine where the voltage is being lost. Replace the low voltage cable, internal charging station harness, or both depending on test and visual examination results.

D-11) If resistance between the ends of both wires is 1 ohm or less, the low voltage cable and internal harness are ok and you need to test the transformer. If transformer is not putting out 28 volts DC, verify that outlet has full power and replace failed transformer/power supply.


E) Solid Red LED

E-2) Disconnect large charging station harness plug from the circuit board.

E-4) If there is 28 volts DC between the red wire and black wire in the plug then then the charging station circuit board has failed and needs to be replaced.

E-5) If there is less than 28 volts DC coming through the red wire and black wire then follow steps D-9, D-10, and D-11 to determine where voltage is being lost or if the transformer has failed.

E-6) If there is more than 28.5 volts DC coming through the red wire and black wire in the charging station harness, then the transformer is putting out too much voltage and needs to be replaced.


F) Flashing Red LED

A flashing red LED indicates that there is an issue with the antenna used to transmit the far (F) signal to help the mower park. An issue with the antenna wire in the charging station base plate will NOT cause a no loop error. It will only affect the mower's ability to properly dock in the charging station.

F-1) If LED is flashing red, inspect antenna wire in charging station base plate.

F-2) If LED is flashing red AND green move on to section G


G) Flashing Red & Green LED

G-2) Disconnect large charging station harness plug from circuit board.

G-3) Using a multimeter test incoming voltage between red wire and black wire in connector. If voltage surges up and down from 28 volts DC to 30 volts DC or more, or up and down from 28 volts DC to to less than 27 volts DC, then the transformer has failed. After replacing the transformer, go to step G-5 to ensure circuit board was not damaged during voltage spikes.

G-4) If there is less than 28 volts DC coming through the red wire and black wire then follow steps D-9, D-10, and D-11 to determine where voltage is being lost or if transformer has failed.

G-5) If there is 28 volts DC coming through the red wire and black wire with no fluctuation, and the charging station LED is solid green but the mower will not pair to the signal from the new charging station board, then the charging station circuit board was damaged and needs to be replaced as well.

H) LED Is NOT Lit

H-2) Disconnect large charging station harness plug from circuit board.

H-3) Using a multimeter test incoming voltage between red wire and black wire in circuit board harness plug.

H-4) If there is 28 continuous volts DC coming through the red wire and black wire in the connector then the charging station circuit board has failed and needs to be replaced.

H-5) If there is NOT 28 continuous DC volts coming through the red wire and black wire then follow steps D-9, D-10, and D-11 to determine where voltage is being lost or if transformer has failed.


I) No Loop Signal Error In Middle Of Work Area Or In Specific Part Of Work Area

If charging station LED is solid green or solid blue:

I-1) With mower sitting where error occurred, press stop button, enter PIN code, and clear "NO LOOP SIGNAL" error.

I-2) Access "Quick Info Menu" on mower

I-4) If one of the loop sensors has an A signal value of 0-50 and all others have a value higher than 60 then the loop sensor with the low value is failing and needs to be replaced.

I-5) If all 4 loop sensors show a value of 0-50 then loop signal from the boundary wire is too weak for the Automower to receive.

I-6) With the A loop signal values still displayed on the mower, push the mower closer to a boundary wire and watch for A loop signal values to rise to at least 60 on all 4 sensors. This will confirm weak signal from boundary wire.

I-7) Remove boundary wires and guide wires from connections on back of charging station.

I-9) If resistance is above 14 ohms, measure resistance between AL & G1, AL & G2, AL & G3, AR & G3, AR & G2, AR & G1 to find which section(s) have the highest resistance in them.

I-10) Walk the path of the boundary wire visually inspecting the wire or soil above the wire. Replace any questionable splices, remove unnecessary islands, and any sections of wire with cracked or broken insulation.

I-11) Measure resistance between AR & AL wire ends and repeat step I-11 until resistance drops to 14 ohms or less.

I-12) Once resistance between AR & AL wire ends is at 14 ohms or less reconnect boundary wires to charging station and test mower in area where it was losing loop signal.

I-13) If after verifying that resistance in boundary loop has been lowered, and mower still loses loop signal in the same area, verify the mower is within at least 75 feet of a boundary wire or island created via boundary wire.

I-14) If signal loss occurs within a few feet of an island or the wires going to and from an island continue to section J (No Loop Signal Or Outside Working Area Error Near An Island)

I-15) If the mower is NOT within 75 feet of a boundary wire or an island formed by boundary wire, then the mower is getting lost because it is unable to receive the signal from the charging station via the boundary wire. You can create a "False Island" to attempt to solve the signal loss in this area. This is when you create an island in the trouble area the size of a soccer ball to help provide signal in that area. The mower will still mow the grass inside the small island via to its drive past wire setting. Verify that mower now picks up the loop signal in this area.

I-16) If loop signal still drops to 0 on the 4 loop sensors in this area after creating the false island then there is likely something in the ground causing interference (Pipe, well pit, power line, etc.) that would need to be identified in order to attempt to solve the continued signal loss.


J) No Loop Signal Or Outside Working Area Error Near An Island

J-1) If loop signal strength goes into negative numbers several inches BEFORE the mower crosses the boundary wire at the island, then the wires coming and going from the island are twisted and causing the signal to reverse. To solve this issue uncover both wires and twist the wires one more time to correct the signal. This must be done at EITHER the island or where the wires connect to the boundary.

J-2) If the mower shows good signal strength around the island, but stops when crossing wires coming and going from island to boundary, then the 2 wires need to be placed closer together to cancel each other out and allow the mower to pass over them. It is ok to place the wires on top of each other or even twist them together as long as they are going in the right direction at the island and at the boundary.

J-3) If the loop signal drops to zero on multiple loop sensors then there is likely something in the ground interfering with the loop signal. Verify this by backing the mower away slowly and see if the signal strength goes back up to the normal operating range of 60 or more on all 4 sensors. In this scenario the best solution is to enlarge the island to the point where the interference stops.



K) Boundary Wire Break, Partial Break, Corrosion, & High Resistance

K-1) It is possible to have multiple breaks, multiple spots of high resistance, multiple partial breaks, or combinations of these issues. Isolate what section(s) of the boundary wire may be causing the issue.

K-1A) Method 1: Remove both boundary wires from the back of the charging station and place a jumper wire between the AL & AR boundary wire terminals on the back of the charging station. If the charging station LED continues flashing blue then go to section D (Flashing Blue LED).

K-1A1) If the jumper wire creates a solid green LED, remove the jumper wire and connect ONE of the boundary wires to the charging station. Then one by one connect the guide wire(s) to the open boundary terminal on the back of the charging station. This creates a new smaller loop between the 2 wires connected to the boundary wire terminals. Watch THIS VIDEO for more information about this process. If none of the combinations of boundary wires and guide wires give a solid green LED, but the jumper wire did, then there is more than 1 break in the boundary and guide wires.

K-1B) Method 2: Use a multimeter to check resistance between each boundary wire and each guide wire, and between guide wires to determine which section(s) have the highest resistance or no continuity. No continuity means there is a complete break. An ohm reading of over 17 ohms means that there is high resistance (corrosion, rust, partial break, bad splice, etc) in the wire.

K-2) Walk the path of the boundary wire in the know bad section and look for any spots where the soil has been disrupted or damaged or any visible cracks in boundary wire insulation. Check the boundary wire in any spots that look suspicious, or were where the wire was previously spliced. This includes connections where guide wires attach to the boundary wire.

K-3) Give the boundary wire a slight tug to ensure it is still solid. If a break is found, repair the wire using a Husqvarna approved weatherproof connector. Or repair the break by soldering the wire and covering it with a shrink tube or other type of weatherproof insulation. Once repaired, bury the the wire or staple it back down and then recheck the resistance in that section to see if there is another bad spot or if that section is now working.

K-4) If bad spot(s) in wire are not found with visual inspection, then a device will be needed to send and trace a signal through the wire.

K-4A) Devices for finding a complete break:

1) AM Radio

3) Wire Tracer/Locator With Meter

K-4B) Devices for finding partial break or high resistance:

1) Wire Tracer/Locator (If resistance is very high)

2) Wire Tracer/Locator With Meter

K-5) If using an AM radio to find a complete break in boundary wire, make sure boundary wire is connected to charging station and charging station is powered on.

K-5A) Slowly wave the AM radio over boundary wire and listen for signal from boundary wire to squelch the radio signal.

K-5B) When the boundary wire signal no longer squelches the AM radio signal it indicates that you have passed the bad spot in the boundary wire. Pull on boundary wire near where signal stops squelching the radio signal to find the break in the wire.

K-5C) Repair the wire using a Husqvarna approved weatherproof connector. Or repair the break by soldering the wire and covering it with a shrink tube or other type of weatherproof insulation. Once repaired, bury the the wire or staple it back down and then recheck the resistance in that section to see if there is another bad spot or if that section is now working.

K-6) If using a Wire Tracer/Locator that sends a tone through the boundary wire to find a complete break, disconnect all boundary and guide wires from the charging station to prevent any interference with tone transmitter.

K-6A) Follow manufacturer's instructions for for proper use of tone transmitter. If using a break finder with a meter on the transmitter and you can not get a high reading on the transmitter then it means that the broken end of the wire is exposed and NOT touching the soil.

K-6C) Pull on boundary wire near the spot where the tone stopped to find the break.

K-6D) Repair the wire using a Husqvarna approved weatherproof connector. Or repair the break by soldering the wire and covering it with a shrink tube or other type of weatherproof insulation. Once repaired, bury the the wire or staple it back down and then recheck the resistance in that section to see if there is another bad spot or if that section is now working..

K-7) If you are unable to find the break or area of high resistance, connect the transmitter of your break finder to the other boundary wire to trace the transmitters signal going in the opposite direction around the boundary loop until the bad spot is found.


L) Parts & supplies for making repairs

Replacement Charging Station Circuit Boards By Model:


Replacement Transformer/Power Supply By Model:

115H, 310, 315, 315X, 415X, 430X, 430XH, 435X, 450X, 450XH, 520, 520H, 535AWD, 550, 550H

115H, 310, 315, 315X, 415X - Original version (While supplies last)


Low Voltage Cable By Model:


Internal Charging Station Harness By Model:


Loop Sensors by model:

Front Loop Sensor 115H, 310, 315, 315X, 415X*, 430X, 430XH, 435X* , 450X, 450XH, 520, 520H, 535AWD*, 550, 550H, 450/550 EPOS (*Requires Firmware Update To Work)


Rear Loop Sensor 115H, 415X*, 435X*, 535AWD* (*Requires Firmware Update To Work)

Rear loop sensors are built in to main board on 310, 315, 315X, 430X, 430XH, 450X, 450XH, 520, 520H, 550, 550H, 450/500 EPOS models


Wire, Connectors, Staples:





M) Suggested Related Videos:


Charging Station And Wire Loop Testing Pics (Click To Enlarge)


Island Related Pics (Click To Enlarge)


Robotic Mower Services, LLC

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