First, it was automatic gearboxes, the dusk-sensing headlights. And now, rain-sensing wipers. Automakers seem to be automating as many mundane tasks as possible, letting the driver focus on higher-level tasks and enjoying the drive.
Just like dusk-sensing lights, rain-sensing wipers detect moisture on the windshield and turn it on by themselves.
They can even modify their wiping speed depending on the type of moisture (snow, mist, or rain), its intensity, and the speed you are driving at.
How Do Rain Sensing Wipers Work?
Many automatic wipers systems use infrared blasters and sensors to detect water droplets on the windshield. They work on the theory that moisture or snow will affect an infrared beam’s reflection angle and intensity.
The entire assembly sits behind the rearview mirror. An infrared transmitter blast repeated rays (or rays) through the windshield at a 45-degree angle.
Sensors next to it analyze the reflection on the beam. If the angle and intensity change, the system infers that there must be some moisture, snow, or water on the windshield and activates the wipers.
Check this too: How Often Should You Change Your Wiper Blades?
The intensity level will vary depending on your cruising speed and light deviation or deterioration intensity.
Top Causes for Failing Automatic Wipers
The automatic sensing and triggering system on most vehicles rarely fails. Since it is stashed out of the way behind the rearview mirror, the chances of tampering with it are minimal.
In most cases, failure will be due to secondary causes that stop the system from working. The most common include:
The Wipers Control on The Stock Not Set to Auto
Most manufacturers still let you override wiper blade controls just as you do with dusk-sensing headlights. There are different positions on the stock for manual speed selection and an off position.
Rain-sensing wipers will only work if you have the stock set to auto. Check and confirm that they are not in another position or turned off in the settings menu.
Different vehicles could have the setting in the infotainment or system setup menu. Consult your manual to see if the setting exists.
Damaged Wiper Stock Switches
The wiper stock is a multipoint switch that could fail under certain circumstances. It won’t send the proper signal to the entire system if it does.
Your sensor assembly and control module might not even detect that the stock is in the auto position. If this happens, the automatic wipers won’t work.
If there is a problem with the switch, the system will work intermittently. In most cases, manual speed selection won’t work or will not always work.
Have the system inspected if you cannot turn on the wipers yourself. You could also try the windshield wash cycle to see if the washer and wiper blades come on.
A Dirty Windshield
Anything, even the tiniest bits of dust and debris, can throw off your rain-sensing wipers. Infrared rays are easy to block.
A dirty windshield could either change how the light reflects or prevent it from heading out at all. Keep your windshield meticulously clean for the best performance.
Avoid putting stickers directly over the sensor that sits behind the rearview mirror on any other sensor you see stuck onto the windshield.
A Cracked or Chipped Windshield Right Over the Sensor
Cracks and chips on the windshield have transparency properties and could even reflect or deflect the infrared rays incorrectly.
This could either trigger false positives or keep the windshield wipers from working at all. This is common if the crack or chips runs within an inch of the entire rain-sensing array.
The Rain Sensing Unit is Unplugged or Damaged
Though very rare, the rain-sensing unit could come unplugged when servicing another part of the vehicle.
Inspect the sensor itself and ensure that the cable leading to it is firmly connected. If someone worked on your vehicle and opened up the dashboard, it will pay to inspect the entire wiring and ensure that it’s well connected and grounded.
If you had to replace the windshield for one reason or another, ensure that the sensor was correctly reinstalled onto the new windshield and properly plugged in.
Losing a sensor after an accident or windshield replacement is common – especially if the mechanic isn’t keen and doesn’t test all related systems after installing your new windshield.
ProTip: Ensure that the replacement windshield is up to spec and doesn’t have any opaque surfaces blocking the sensor assembly
Damaged Windshield Wipers
Sometimes, your rain-sensing wiper sensors and controllers could be working fine, but you see no effect because your wipers are damaged.
Test their performance by activating them manually or activating a windshield wash cycle. If nothing happens, chances are:
- The wiper stock switch system is faulty
- The wipers are stuck
- There is a problem with the wiper motors
You will need help troubleshooting the problem and fixing the fault for a permanent fix. Such failure is not expected unless you drive a high mileage vehicle or have a factory defect on your hands.
Will Tinting My Windows Affect Rain Sensing Wipers?
No. Installing legal ting to your windows won’t affect rain sensors since they sit on the windshield. Even if you tint the windshield, legal tints aren’t dark enough to obscure the sensor’s operation.
The only effect you might get is your automatic headlights turning on a bit earlier since they use an ambient light sensor to detect darkness. A tinted windshield will reduce how much light filters through, making them kick on sooner than usual.
How to Test Rain Sensors
Luckily, testing the sensor is simple. You have to make the area next to the sensor a bit wet.
- Switch the car on
- Move the wiper switch to the automatic control position
- Use a spray can spray some water onto the sensor area from the outside of the windshield
- This should trigger the wipers in a moment
- Spray more water to see if this alters the operating speed as it should
ProTip: Even though a fault in the system won’t trigger a check engine light, some vehicle log performance and errors can be read from the unit’s memory using the right diagnostic tool.