Diagnosis
The suction tube inside the detergent bottle is either clogged, disconnected, or the black low-pressure soap tip is blocked or missing.
How to Fix It
First, check the obvious: make sure you're using the black spray tip labeled "SOAP" or "LOW PRESSURE." The injector only works with that tip installed. Then, remove the detergent bottle. Look at the suction tube—the clear plastic hose that goes into the bottle. Make sure it's attached to the nipple on the cap and isn't kinked. Blow through the tube to clear any clogs. Finally, with the washer running on low pressure (black tip), hold your thumb over the end of the suction tube—you should feel a strong suction.
If That Didn't Work
The check valve inside the injector itself might be stuck. This is a small plastic part where the suction tube connects to the washer. You can try gently tapping that area while the machine is running to dislodge any debris. Don't take it apart, as the springs inside are easy to lose.
Heads Up
Never use bleach or corrosive chemicals in the soap tank. They will destroy the rubber seals and plastic parts in the injector system. Stick to detergents made for pressure washers. Also, always rinse with clean water using a high-pressure tip after applying soap.