What Happens When a Linear Actuator Fails? A 7-Point Checklist for ABB Motor-Driven Axes

I review motor and actuator integration specs for a living—roughly 200 packages a year. In our Q1 2024 quality audit, 14% of field-returned linear actuators had nothing wrong with the actuator itself. The fault was upstream: drive settings, feedback noise, or a mechanical issue in the drive chain.

So when someone asks 'what happens when a linear actuator fails?', my answer is usually: maybe nothing. Sometimes the actuator is the victim, not the cause. The checklist below is the one I use before I authorize a replacement. It applies mostly to industrial servo linear actuators and ABB motor-driven packages. My experience is based on about 200 field failure reviews with ABB pump motor and servo axes. If you're working with a small 12V actuator in a lab fixture, your experience may differ.

Use this when an axis stops moving, loses position, or trips the drive on overload. It is not a substitute for the drive's commissioning manual. It's a triage order.

What a failure actually looks like

From the outside, a failed actuator looks like a sudden mechanical death. One cycle it moves, next cycle it doesn't. The reality is most failures are systems-level and show up as patterns first: a position error building over three days, a current spike when the oil is cold, or a faint increase in noise.

What you'll see in the field, in rough order of frequency: loss of position, audible hum with no movement, erratic speed, and thermal alarms. Sometimes the axis just goes limp. No movement at all. Nothing. The earlier you catch it, the less likely the actuator is actually damaged.

The 7-point checklist

1. Verify the power supply and drive health

Measure line voltage at the drive terminals, not at the panel breaker. A voltage sag that lasts half a cycle is invisible on a normal multimeter. Use a scope or the drive's own voltage monitor. We had a servo linear actuator that kept losing position. Everyone blamed the ball screw. The actual cause was a 12% voltage sag during rapid traverse—a corroded terminal block, 90 ms each cycle. A $600 terminal repair fixed it. The $4,200 replacement quote was wrong.

Also check the drive's DC bus ripple. If main capacitors are aging, the bus may collapse under the actuator's acceleration current. The motor sounds like it's struggling, but the problem is the supply.

2. Read the drive's position error log

The drive log is the flight recorder. If the error grows gradually, think mechanical wear. If it appears suddenly, think electrical noise, a loose connection, or a gain issue. Check the history, not just the current alarm. Most ABB drives store enough detail to show whether the error preceded the failure or followed it. That sequence matters. If the error appears after the axis decelerates, the issue may be the tuning. If the error was already there before the axis stopped, suspect backlash or a feedback problem.

3. Free the drive chain and feel for trouble

With power off and brakes released, move the axis by hand—or use a torque wrench if it's a high-ratio gearbox. You're feeling for tight spots, rough spots, or resistance that repeats at the same position. A worn coupling, a bent lead screw, or a misaligned guide rail appears here. Do this over the full stroke, not once. We've seen a contamination mark that only appeared at the end of travel.

In one ABB pump motor package we reviewed, the coupling between the motor and the actuator was cracked. At low speed it was fine—not great, not terrible, serviceable. At rated speed it vibrated, then tripped on overload. The actuator was fine. The drive chain was not.

4. Inspect grounding and cable connections

Servo actuators hate electrical noise. A loose shield connection or a missing ground braid causes random position jumps. Check the connector torque and the shield bond. If the cable flexes with the axis, check the bend radius. We saw a 2,000-hour specified cable fail at 400 hours because someone secured it with a cable tie at too tight a radius. A lesson learned the hard way.

Also inspect the connector pins for scorch marks or discoloration. A single pin with a poor crimp can drop one feedback phase intermittently. It won't show as a full alarm; it will show as a position error that comes and goes.

5. Measure current at no load and at operating load

Use the drive's current monitor. Compare it to the actuator motor's nameplate current. If you're consistently above 90% of rated current, the actuator is undersized for the duty cycle—not broken. If current is normal but position is lost, skip down to feedback. Also record the winding temperature after 20 minutes of steady operation. An IR thermometer aimed at the housing tells you if the thermal path is blocked by dirt or oil.

6. Test the feedback device and brake

In a servo linear actuator, feedback is the nervous system. A noisy encoder or resolver signal can make the drive oscillate or settle on the wrong position. Swap in a known-good cable before you condemn the actuator. If there's a holding brake, check the release time. A dragging brake will heat the motor until it trips thermally. The replacement quote was $1,800. Actually, $2,100 once we added the feedback cable and commissioning. Still cheaper than replacing an actuator that wasn't broken.

7. Review duty cycle and ambient temperature—the one people ignore

Most people stop at electrical checks. I make a point of asking about the actual cycle. Is the actuator rated for continuous duty but used with rapid reversals? Is it mounted where the ambient temperature exceeds the datasheet? We had a 50,000-unit annual line where the actuator torque was correct on paper, but the internal temperature ran 22°C above the insulation rating. The motor thermal switch opened, then the feedback started acting up. Specifying a larger actuator—or adding forced cooling—solved it. Not ideal, but workable.

The same logic applies to an ABB motor connected to the actuator. A motor is not a fixed component; its rating changes with duty and cooling. The most common mistake we audit is choosing a motor and actuator from two separate catalogs and assuming they will work together at maximum rated torque. The nameplates say otherwise.

Three common errors I still see

First, replacing the actuator without checking the drive parameter set. If the axis was working with a certain inertia ratio and you install a different motor/actuator combination, the tuning gains may no longer be valid. The new actuator can vibrate or trip on positional deviation—and the replacement gets blamed.

Second, assuming 'overhaul' means 'same as new.' A rebuilt actuator with new seals and bearings may still have the old feedback device or an aged harness. That's fine if you know the history. It's a risk if you're just chasing the lowest quote.

Third, buying before measuring. We rejected 12% of first delivery packages in 2024 because the specs didn't match the actual system. That rejection was not the vendor's fault. The buyer specified from memory, not from the nameplate.

If the actuator really is dead

After these checks, some actuators are genuinely dead. That's when you start buying. And this is where my view gets firm: ask what's NOT included before 'what's the price.' The vendor who lists all fees upfront—even if the total looks higher—usually costs less in the end. A lower base price without the mating connector, software update, or commissioning visit is not a lower price. It's a partial one. On a servo axis, the cable and the drive tuning are not optional extras. They're part of the installation.

On an ABB motor-driven axis, match the actuator and motor inertia and thermal class. That matters more than the commodity part number. The current cycle of ABB motor news is heavy with efficiency classes and digital motor data—useful, but it won't tell you if a legacy actuator is the right replacement for your installed drive chain. Check the original order, not the online product photo.

One more note: when you get quotes, ask the vendor to confirm the feedback type, brake voltage, and mounting flange. These three items cause more after-installation surprises than the price itself. A quote that includes these confirmations is worth more than a cheap one that assumes compatibility.