How to Test a Windshield Wiper Motor

by Paul Vaughn

Windshield washer circuits work in conjunction with your windshield wipers. A non-reversing permanent magnet motor drives your washer pump. The motor is controlled by a set of contacts in the wiper switch. The wiper switch is located on the driver side on the column or by a knob located in the dash panel. In either case, the testing procedure is the same. Here's how to do it.

Testing the wiper motor

Step 1

First, locate the wiper motor. The wiper motor is usually located in the engine compartment typically on the fire wall. If you have trouble finding it, consult the owners manual for your vehicle.

Step 2

Make sure the wiper motor and wiper blades are free of obstructions such as road debris, bugs and leaves. If the blades and motor are not able to move due to debris, do not activate the circuit until they are removed. Obstructions will cause an overload condition that will damage wiring, washer motor and fuses.

Step 3

Check the service manual for your year and model to determine which type of washer motor your vehicle has. Some washer motors operate only when the ignition is on. Others operate through relays and are always hot. Use your DVOM to check for power at the washer motor terminal. Touch the DVOM ground lead to a solid ground source such as the engine block. Touch the positive lead to the positive terminal on your motor. If there is no power to your washer motor, check for blown fuses and damaged wiring to the washer motor.

Step 4

Repair any wire damage using your wire splicing tool and wire connectors. Locate the fuse box and remove the cover. Use the fuse pattern shown on the cover and locate the wiper motor fuse. Test the fuse using your twelve volt test light. Clip the ground lead to a solid ground source and touch the positive lead to each side of the fuse. If the test light lights up on both terminals, the fuse is good. If your test light only lights up on one side of the fuse or neither, replace the fuse. Use your needle nose pliers to remove the fuse and install a good fuse. Replace the fuse box cover and proceed to the next step.

Step 5

Your wiper motor is usually a non-reversing type and is grounded through the case. Visually inspect the mount bolts. Look for rust and corrosion. If these exist, replace the mount bolts with new ones. They can be purchased at your local auto parts store or dealer. Use your open end box end wrench to make sure the mounting bolts are securely tightened to the fire wall.

Step 6

Turn the ignition to the on position. Use your DVOM to check for voltage drop from the washer motor to its ground source. A voltage drop of less than 0.5 volts is acceptable. If the volt drop is greater, visually inspect the the circuit for poor connections. If the ground circuit is questionable due to corrosion, use a jumper wire to connect the motor case to a solid ground source. If your washer motor operates with the jumper wire attached, the ground circuit is defective. Replace mount bolts or faulty wiring as needed.

Step 7

If the power source and grounding circuit are good, the washer motor itself is defective. This type of motor cannot be rebuilt and must be replaced. You can find a new wiper motor at your local auto parts store or dealer. Consult your service manual for the removal and replacement procedure.

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