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If your impact driver keeps spinning when the trigger isn’t pulled, the most likely cause is a trigger switch that isn’t returning all the way to off. Either dust and debris are holding it partly in, or the switch has worn out or failed internally. Less often, the electronic controller has failed, moisture has gotten inside, or a poor battery connection is making the electronics act up. Whatever the cause, pull the battery now and leave it out until the tool is fixed. A driver that runs on its own can wind a bit into a hand, a glove, or a sleeve.
Make It Safe Before Anything Else
- Remove the battery. If the tool is running, don’t grab the bit or the chuck to stop it. Release the battery latch and pull the pack out.
- Remove the bit so the tool can’t catch anything during our research.
- Check for heat and smell. A housing that’s hot near the trigger, a burnt-electronics odor, or melted plastic points to a failed switch or power transistor. Set the tool on a nonflammable surface away from anything combustible, and don’t put a battery back in.
- Don’t store it with a battery attached until the problem is solved.
Which Version of the Problem Do You Have?
“Keeps spinning” covers three different behaviors, and each points somewhere different.
- It coasts for a second or two, then stops. Some run-down with no load can be normal. But if a tool that used to stop instantly now freewheels, it has lost its electric brake. On brushed tools the brake circuit lives in the trigger switch, and on brushless tools it’s handled by the control board.
- It keeps running at speed after you let go, until you pull the battery. Either the switch isn’t returning to off, or the switch or controller is stuck in the on state.
- It starts the moment you insert a battery, with nobody touching the trigger. That’s an electrical fault, usually a shorted switch, a shorted power transistor, or a failed controller. Don’t keep testing it.
Causes, From Most to Least Likely
1. A dirty or sticky trigger
Fine drywall dust, MDF dust, concrete dust, and sticky residue from caulk, adhesive, or a spilled drink can pack into the gap around the trigger. A variable-speed trigger only needs to sit slightly in to keep the motor turning. A weak or broken return spring causes the same symptom. This is the cheapest fix, and the one to rule out first.
2. A worn or failed trigger switch
Switch contacts wear, grease can migrate onto them from nearby parts, and on brushed tools arcing can weld contacts together. On many brushed tools, the trigger switch also contains the speed-control transistor (a MOSFET). When those transistors fail, they usually fail shorted. That means full power reaches the motor no matter where the trigger sits.
3. A failed or locked-up controller (brushless tools)
On a brushless driver, the trigger sends a signal to a control board, and the board drives the motor. If the board misreads the trigger or locks up, the motor may keep running, or the direction selector may stop responding. A telltale sign is that removing and reinserting the battery clears the problem for a while, then it comes back.
4. Water or moisture
Rain, a wet job site, or condensation when a cold tool comes into a warm shop can leave moisture across the trigger’s sensing circuit or start corrosion on the board. The tool may behave once it dries, but corrosion can bring the problem back.
5. Battery and contact problems (some models)
Dirty, corroded, or loose battery terminals cause voltage dips that can make electronics act erratically. This is rarely the root cause of run-on, but it’s the fastest thing to rule out. Try a different, known-good battery.
Check Sequence
- Battery out, trigger test. Squeeze and release the trigger by hand 15–20 times. It should snap back crisply to the same rest position every time. If you have a second tool from the same brand, compare the feel.
- Inspect with a flashlight. Look into the gap around the trigger and the forward/reverse selector for packed dust, grit, or sticky residue.
- Blow it out. Wear safety glasses and use compressed air around the trigger while cycling it.
- Flush with a contact cleaner. Use a plastic-safe, residue-free electronics contact cleaner, or 90%+ isopropyl alcohol. Spray it into the trigger gap while working the trigger in and out. Skip brake cleaner, which can attack the plastic, and general-purpose penetrating oils, which leave a film that collects more dust. These solvents are flammable, so the battery stays out and the tool dries for several hours, ideally overnight.
- Clean the battery contacts. Clean the terminals on the tool and the pack with a dry cloth, or a cotton swab lightly dampened with contact cleaner. Look for discoloration or melted plastic around them.
- Controlled power-up. Clamp or set the tool on a bench pointing away from you, with no bit installed. Keep your hand clear of the trigger and insert a known-good battery. If it starts on its own, pull the battery immediately. That’s an electrical fault, and cleaning won’t fix it. If it stays off, pull and release the trigger a few times. It should stop the instant you let go.
- If it got wet: Keep the battery out and let the tool dry for 48–72 hours in a warm, dry room. Don’t use a heat gun, which can warp the housing and damage the electronics. Then repeat the controlled test.
Fixes That Work
Cleaning solves a sticky trigger more often than you’d expect, especially on tools used for drywall or demolition.
Replacing the trigger switch is the standard fix when cleaning doesn’t help. Order the part by the exact model number and the type or version code on the nameplate, because switches change between versions of the same model. Most housings come apart with Torx screws. Photograph the wire routing before you lift anything out. On many tools, someone comfortable with small electronics can do the swap in 20–45 minutes.
On brushless tools, the switch is often sold together with the control board, and on some models it’s built into the motor assembly. That makes the part more expensive, so compare it against the price of a new bare tool before you buy.
Never tape, wedge, or bypass a switch to keep a faulty tool in service. A tool that can start on its own isn’t safe to keep using.
Repair or Replace: Cost Comparison
Prices vary by brand, model, and retailer. Treat these as 2026 ballpark ranges.
| Option | Typical cost | DIY time | Makes sense when |
|---|---|---|---|
| Clean trigger area | $5–$15 (contact cleaner) | 15–30 min plus drying | Always try first |
| Separate trigger switch | $15–$50 part | 20–45 min | Tool is otherwise in good shape |
| Combined switch and controller module (brushless) | $40–$140 part | 30–60 min | Part costs under about half a new bare tool |
| Independent repair shop | About $60–$150 total (shop rates often $75–$120 per hour, plus minimums) | None | You’d rather not open the housing |
| Manufacturer warranty service | Usually no charge for covered defects | None | Tool is within its warranty period |
| New tool-only impact driver, major brands | About $70–$200 depending on line and sales | None | Repair would cost more than half the replacement |
Warranty Notes
Check your coverage before you open the housing. Taking the tool apart yourself can complicate a warranty claim. Typical standard terms for cordless tools are:
- Milwaukee M18 and M12 tools: 5-year limited warranty on most tools. Batteries have shorter, separate terms. Without a receipt, coverage is generally based on the manufacture date.
- DeWalt: 3-year limited warranty on most power tools, plus one year of free service and a 90-day satisfaction guarantee.
- Makita 18V LXT: 3 years on tools, batteries, and chargers.
- Ryobi 18V ONE+: 3-year limited warranty on most tools.
Terms vary by product and can change, so confirm against the warranty statement for your model. Water damage and abuse are commonly excluded. A switch that fails in normal use is the kind of defect these warranties are meant to cover. Keep your proof of purchase, and check the U.S. Consumer Product Safety Commission recall database for your model number. Switch and overheating problems have triggered power tool recalls before.
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