How to Troubleshoot a Rear Windshield Wiperby Jack Hathcoat
Rear windshield wipers work exactly the same as front wipers. There is a parking circuit built into the motor that seats the wipers when turned off. A wiper switch and related wiring control the on-off operation and wiper speed. Finally, a leverage arm is connected from the motor to a transmission assembly, that in turn connects to a wiper arm. The arm then holds a rubber squeegee --- a wiper blade --- that sweeps across the windshield. Each item must be in good order for the system to work correctly.
Remove the back cover to gain access to the wiper assembly. Follow the manufacturer's directions in the service manual. Unplug the wiper motor connector. Probe the voltage supply plug with a voltmeter and make sure voltage and ground are present. Move the wiper function switch through all positions to determine proper voltage at the plug. If there is no voltage, check the voltage supply to the dash switch and check the rear wiper fuse.
Remove the wiper switch from the instrument panel. Test for voltage to the switch. Move the switch through its functions and make sure there is voltage present at each plug location. Follow the manufacturer's guidelines for switch removal and test procedure for each specific wire location and function.
Test the rear wiper relay. Before reaching the wiper motor, the wiper switch sends power to a relay. This relay serves two purposes. It allows a small current signal from the switch to control a large current that powers the wiper. Designers can then use a small dash switch and wiring, keeping the instrument panel less cluttered. The relay also isolates the wiper circuit, which helps keep out wiper radio noise. Failed relays are usually obvious, with burned and discolored contacts. Test the relay with a voltmeter. Turn the wipers on. The relay should "click" when energized. Follow the manufacturer's guidelines for specific relay locations and test procedures.
Inspect the remaining components: wiper arm, wiper blade and wiper transmission assembly. They should be in good shape --- not bent nor binding in any manner. Inspect the transmission arm bushings for excessive wear. Replace any defective parts.
- Many manufacturers are using a solid state, electronic wiper module to control voltage supply and intermittent wiper function on newer cars. This eliminates the old-style relay function. Worthwhile testing information regarding these modules is difficult to find. You can use process of elimination to isolate it as the problem. Make a fused power supply wire and ground wire. Apply direct voltage and make the motor run. If it runs and is not growling and noisy, it's okay. Remove the wiper switch and inspect it. Test it for proper voltage supply. If it's okay, then by process of elimination, the module is suspect. Replace it if the associated wiring is good.