Horizon Treadmill 'LS' — Low Speed Limit Error Fix

What it means

'LS' on a Horizon treadmill (Low Speed) means the speed reading dropped below the minimum the console expected during a workout — usually because the running belt was slipping, the motor stalled briefly under load, or the speed sensor lost the signal for a moment.
It's a softer error than E1 or E5 — the treadmill often keeps running afterwards rather than cutting power — but it points at the same family of problems: belt, deck, sensor, or motor load.

Affected Models

Horizon T202, T303
Horizon 7.0 AT, 7.4 AT, 7.8 AT
Horizon Adventure 3, 5
Horizon Studio Series
Some older Vision Fitness models on the same controller

Common Causes

Running belt slipping on the front roller under load
Belt too loose — slips when you take a heavy step
Speed sensor magnet loose on the front pulley
Speed sensor cable intermittently breaking
Dry deck dragging the belt so the motor stalls briefly
Worn motor brushes causing momentary stalls
User weight at or above the treadmill's rating
Controller calibration off — expects a higher speed than the actual setting

How to Fix It

Check belt tension.

Power off and unplug.
You should be able to lift the centre of the running belt 50–75 mm (2–3 inches) off the deck.
If you can lift it more than that, the belt is too loose and will slip under your stride, dropping speed momentarily and triggering LS.
Turn the two rear roller bolts equally — a quarter-turn at a time on each side — to tighten, then re-measure.
Lubricate the deck.

A dry deck causes friction; friction causes the belt to slip and the motor to lag.
Lift one side of the running belt and apply silicone treadmill lubricant in 3–4 spots across the deck.
Walk on the belt for several minutes at a slow speed once you power back on, so the lube spreads.
Lube every 50 hours of use to prevent LS coming back.
Check the belt is centred.

If the running belt has drifted to one side, the edge can catch on the deck shroud, drag, and cause sudden speed drops.
With the mains on, set a slow speed and watch the belt — it should run dead centre.
If it's drifting right, tighten the right rear roller bolt a quarter-turn; if drifting left, tighten the left.
Adjust slowly and re-check.
Reseat speed sensor and magnet.

Unplug and open the motor cover.
Check the speed sensor is mounted within 3–5 mm (1/8 inch) of the magnet on the front pulley, and that the magnet itself is fixed firmly in its slot.
Push the speed sensor's connector firmly home at the motor controller.
A loose magnet that gets bumped by the sensor cable, or a sensor that's drifted away from the pulley, gives the intermittent dropouts that trigger LS.
Run service-mode diagnostics.

Hold Stop + Speed Up to enter service mode on most Horizon models (the exact combination is in your manual or under the console).
Run the speed test.
Watch the readout: a steady, smooth count means the sensor is fine; jumps and drops mean the sensor or magnet is the cause.
Inspect motor brushes (high-hour treadmills).

After 1000+ hours of use, motor brushes wear and the motor occasionally stalls under load — particularly during heavier steps.
Brushes are behind two small caps on the motor; check whether they're worn down to a stub.
Brushes are cheap (£10–£20 / $10–$25) and a short replacement.
If LS keeps coming back, replace the belt or call support.

If tension, lube, alignment, sensor, and brushes all check out, the running belt or deck is probably worn — slick under, dry, or warped enough to slip under load.
A new belt + deck flip restores most older Horizon treadmills to like-new operation and is well worth doing if the rest of the machine is in good shape.
Order from Horizon parts using your exact model number, or contact Horizon technical support.

When to Call a Professional

LS is normally fixable with belt tension and lubrication — squarely owner-territory.
Call a technician if you find a worn deck (deck-flip on most models is awkward) or suspect the controller is miscalibrated.
Always unplug the mains before working on the belt or opening the motor cover.

Frequently Asked Questions

Is LS a serious error on my Horizon treadmill?

Less serious than E1 or E5, but it's a warning you shouldn't ignore.
LS means the controller noticed the belt momentarily moving slower than the console set — usually because the belt slipped under your weight, the motor stalled briefly, or the sensor missed a count.
If you fix it now (lubricate the deck, set the belt tension, reseat the sensor), the treadmill keeps running fine.
If you ignore it, the same conditions that cause LS — friction, slipping, motor strain — eventually trigger the more serious E5 (motor overload) or HOt (overheat) errors, and you end up replacing belts, brushes, or the controller instead of doing five minutes of maintenance.