How to Diagnose a Problem With Windshield Wipers in a Car

Place the vehicle in "Neutral" for a standard transmission or "Park" for an automatic. Set the emergency brake and raise the hood. Locate your main fuse box and look for the windshield wiper fuse and-or relay. The fuse will be a type of glass tube or a spade design. Visually inspect the fuse to see if the filament inside either type is internally disconnected or blackened. Replace the blown fuse. Pull the relay out and swap it with another relay of the same pin design and voltage. Turn the windshield wiper on and see if it functions. If it does, the fuse or relay was the problem.

Turn the windshield wiper on; you might also have to turn the ignition key to the "On" position. Look and listen for windshield motor movement and sound. If you see no movement and hear no sound, turn the windshield motor switch off. If the wiper motor is concealed under the top outside vent panel, use a screwdriver to remove the panel. If your windshield washer motor operates by a vacuum system, check the vacuum hose for cracks and loose connections from its source to the windshield motor. Repair the vacuum hose or tighten the connection.

Examine the wiper rod linkages. You will see a main driving arm and two wiper rod arms, supported by pivots. The linkage rods are connected by spacers and cotter pins, or with small nuts. Make certain the pins or nuts have not come loose or fallen off the arms. The arms should not be bent or disfigured. Look for twigs or small stones wedged between the linkage arms and remove them. Move the linkage arms manually to see if they cycle. Spray some white grease on all the linkage arm connections and pivot points.

Inspect the windshield wiper motor drive gear where it connects with the main linkage rod. The gear or sleeve should not be broken or misaligned. Feel the mesh of the mating gears for tautness. Tighten the wiper motor mount bolts with a socket and ratchet, or use a screwdriver, if it is equipped with screw fasteners. If the windshield wiper motor has a ground strap, unscrew the ground strap with a screwdriver and clean the connection with a piece of sandpaper, then reconnect it and tighten it.

Inspect the connector wire to the windshield wiper motor for a clean and tight fit. Turn on the ignition key and the windshield wiper switch. Clamp a lead from a test light to ground and stab the hot wire on the wiper motor with the test light probe. If you have voltage, the problem lies with a defective wiper motor. Check your windshield washer pump motor in the same fashion by having an assistant activate the pump button with the key and switch on. Ground the test light lead and stab the test light probe into the hot washer pump wire -- voltage at the washer pump motor means the small motor is not functioning.

Inspect the condition of the wipers blades if they fail to make a clean pass over the windshield and leave streaks. Replace them, if necessary, by unclasping the old blades and snapping the new ones on in the frame guides.