While every generation and model of Audi will have slightly different dashboard indicator and warning lights, every one of these sends a specific message to the driver as per the activities and the operations within the Audi. These messages are normally triggered by the respective sensors to make the drive easier, safer and comfortable during all times of the day and in all types of weather conditions. One of such sensors is rain/light sensor which is standard equipment on all the newer models but the same can be retrofitted in old models of before 2015 such as Audi A4L, Avant, Allroad, Audi A5 cabriolet, Audi Q5, Infinity Q50 etc. This sensor also triggers a message when anything goes wrong with the sensor and its functioning and your dashboard lights up with the corresponding message as follows:
Automatic headlights: malfunction! See owner’s manual
Automatic wipers: malfunction! See owner’s manual
Automatic headlights/automatic wipers defective
With the display of these messages, windshield wipers, automatic headlights and other functions are put to the cease by the automatic functions of the car.
Where this rain/light sensor is located?
You’ll find this sensor inside the glass of windshield near the rear view mirror. The main function of this sensor is to analyze the overall brightness outside the car and control the automatic daytime running light/main beam headlights and automatic wipers. With the help of this sensor, car tune itself according to the outside weather and environment and make the automatic headlights and wipers function accordingly.
Rain/light detection sensor mechanism
The rain sensor works on the principal of total internal reflection by making the use of infrared radiations. If the water droplets are found on the windshield the infrared light beam scatters and reflects back at different angles showing that there is rain outside and windshield in wet. In case of no rain or a dry windshield, the full amount of light returns to the photodiode. When the amount of light reflected back is found reduced than the level preset by the software inside the sensor, it automatically switches on the wiping mechanism of the car to start the drying process.
The software also determines the speed of the wipers depending on the amount of moisture accumulation. However, this speed of wipers changes according to the detection of moisture by the sensor.
The light sensor is located at the base of the windshield under the defogger grill. The sensitivity of the sensor is either set by the auto manufacturer or the driver. The sensor is activated by the lighting conditions at dawn or dusk. If the sensor detects dark outside conditions or a car is driven in enclosure such as car park garage the system will illuminate the headlights as auto function. The lights may switch off up to five minutes after the engine has been turned off. The driver has the ability to bypass the functions of the automatic headlamps by operating the light switch or some other device in the car. If the driver inadvertently leaves the lights on, a reminder chime will ring so the driver can turn them off. Similarly, the driver can also switch the lights ON when there is dark and DRLs are not turned ON automatically.
Functional limitations of rain/light sensor
There are limitations to both sensors, as there are certain conditions that become difficult for a computer to understand. The rain sensors can be thrown off by debris or dirt on the windscreen which alters the amount of light reflected back, the dirt can also affect the light sensors which are blocked off from any light. This can be remedied with a squirt of windscreen wiper fluid and a quick wipe across the windscreen. If the light persists then you may want to have a car wash.
The light sensor is also thrown off by fog or intense rainfall since light can still be detected. And since the light sensor only detects the light, so they comes out ON even when the something is blocking the sunlight or the driver is parking the car without realizing if the darkness level is due to sunset or just a temporary blackout during the day.
Is it safe to drive with rain and light warning light on?
Relying on automatic systems can leave you in trouble when they decide to stop working. You must be prepared to take control of the vehicle in all situations. For safety reasons, the dipped beam headlights will then be switched on permanently when the light switch is set to the AUTO position. However, you can still switch the lights on and off in the normal way with the light switch. If the rain sensor is defective, the functions operated via the windscreen wiper lever will still be available.
If your rain and light sensor warning light is on when there is no rain or when it is still bright outside then in the first place, it is better that you give your car sometime to adjust to the outside environment as sometimes the software may not adapt quickly to the changes in the outside conditions and fails to function properly.
If this technique doesn’t work and the auto functions of light and rain sensors do not resume to their stored function then the light/rain sensor is malfunctioning.
How to fix the malfunction rain/light sensor
Though, the last resort option is the replacement of faulty sensor but before doing that, try to clean and leave the vehicle at some warm place. Otherwise, replacing the faulty sensor with the new one is a quick and easy fix to address this warning message.
Replacement Guide
You can replace the sensor by yourself or may contact any professional mechanic or an Audi dealer to have the replacement done for your model. Removal of a faulty sensor and installation of a new one can go about as follows if you wish to do it on your own:
Removal Instructions:
- Carefully disconnect the electrical connector and gently press down retaining spring.
- Use a small screwdriver to release from the lock
- Without exerting force, release the sensor and gel pad slowly and gradually pulling on the plug side.
Installation Instructions:
- Clean the assembling area with an alcohol-based cleaner before installation
- Gently press on the two spring clips on the retaining frame position to position the sensor in the assembly area. Now audibly engage the retaining clip by increasing the pressure on the right and then the left spring arm in turn. The sensor should not be tilted while increasing pressure. Do not engage both spring arms at the same time.
- Lock electrical connector in connector housing and check if it is fitted correctly.
Post-replacement checking new rain/light sensor
If the new rain/light sensor is installed properly then the warning message should have been disappeared and the sensor should work perfectly fine. You can ensure this by simulating the precipitation on the windscreen and the wipers should start and adapt quickly to the simulated rain intensity. If it does, the installation is successful but if there is no response, but the manually activated wiper stages are working properly then you may need to take your car to the dealer for further diagnostics.
