my makita impact driver feels weak, it struggles to drive screws that my older makita handled fine, battery is charged.

Diagnosis

The loss of power in the Makita XDT16Z is most frequently caused by the tool being inadvertently shifted into a low-torque operational mode. Unlike older, single-speed Makita impact drivers, the XDT16Z features an electronic speed and torque selector. If the tool is set to a precision mode, the motor limits the RPMs and the hammer mechanism doesn't engage with full force, making it feel "weak" or "stalled" when driving heavy-duty fasteners into dense lumber. Another common root cause is a failure in the battery communication circuit. Even if the battery shows a full charge on the external LED indicator, a degraded cell or a dirty terminal can cause a voltage drop under load. When the trigger is pulled, the tool demands a massive spike in current; if the battery cannot provide this, the electronic controller throttles the power to prevent a complete shutdown, resulting in a noticeable lack of "kick" during the impact phase. You can confirm this by swapping the battery with a high-discharge 5.0Ah or 6.0Ah LXT pack to see if the torque returns.

How to Fix It

To restore full power to your XDT16Z, follow these precise steps to ensure the tool is in maximum performance mode:

1. Locate the mode selection button/switch on the base of the handle, typically near the battery interface.
2. Cycle through the settings until the LED indicator shows the highest power setting (often indicated by a specific light pattern or a "High" marking).
3. Ensure the trigger is fully depressed. The XDT16Z uses a variable speed trigger; if you are pulling it halfway, the tool will not engage the full impact mechanism.
4. Verify that the battery is seated firmly. Remove the battery, use a cotton swab with 90% isopropyl alcohol to clean the copper terminals on both the tool and the battery, and snap it back in until you hear a definitive click.
5. Test the tool on a 3-inch deck screw in a 4x4 post. If the tool spins without "hammering" (the loud rattling sound), the internal anvil may be stuck; give the chuck a few sharp taps with a rubber mallet to loosen the internal striking mechanism.

If That Didn't Work

• Check for Battery "Voltage Sag": If you are using an older 1.5Ah or 2.0Ah battery, the internal resistance may be too high for the XDT16Z's high-demand motor. Test the tool with a 5.0Ah (BL1850) battery. If the power returns, the original battery has suffered internal cell degradation and can no longer handle the current draw of an impact driver.
• Inspect the Chuck for Debris: Small shards of metal or sawdust can migrate into the hex-drive sleeve. This creates friction that steals torque from the motor. Use a can of compressed air to blow out the 1/4" hex opening and apply a single drop of dry PTFE lubricant to the sleeve to ensure the bit is seating fully and rotating freely.
• Evaluate the Trigger Switch: The XDT16Z uses a digital trigger. If the internal potentiometer is worn or contaminated with sawdust, it may not be sending a 100% "on" signal to the controller. If the tool feels inconsistent—strong one moment and weak the next—the trigger assembly likely needs replacement.
• Internal Hammer Lubrication: If the tool sounds "muffled" and lacks the sharp snap of an older model, the internal grease may have thickened or migrated. While these are sealed units, a professional service to regrease the hammer and anvil assembly can restore the lost kinetic energy.

Heads Up

• Avoid using "cheap" aftermarket batteries; the XDT16Z has a sophisticated communication chip that may throttle power if it detects a non-genuine battery to prevent overheating.
• Never run the tool at full speed without a fastener engaged for more than 30 seconds, as this can cause the brushless controller to enter a thermal protection mode, temporarily reducing power.
• Periodically clean the vents on the motor housing with compressed air to prevent dust buildup, which causes the motor to run hotter and lose efficiency.
• Always ensure your bits are fully seated in the chuck; a bit that is only halfway inserted will wobble, causing the energy to dissipate and making the tool feel weaker than it actually is.