Short answer: The rear fog light is a powerful rear light that helps make your vehicle more visible to those behind when visibility is significantly reduced. Learn the control location and indicator symbol from the vehicle manual. Use the light in the conditions described in the manual and verify it is off when no longer needed. The front fog light, rear position light, and brake light serve different functions.
How do you know which light you have turned on?
Perform the initial check before setting off and while the vehicle is safely parked. Find the rear fog light in the exterior lighting section of the owner’s manual. Compare the symbol in the manual with the button, lighting stalk, or screen in the vehicle. In some vehicles, the controls for the two fog light functions are close together. Do not decide based solely on the button position without learning which is front and which is rear. Also learn from the same section what you should see on the driver display when you turn on the control.
The Volvo V90 owner’s manual explains that the rear fog light is more powerful than normal rear lights and helps alert drivers behind in low visibility conditions. In the same example, the relevant symbol lights up on the driver display when the rear fog light is activated. This description helps identify the function. Use the vehicle-specific manual for the number of lights on your own car, where they are visible from outside, and the conditions that activate the control.
| Light | Distinguishing point |
|---|---|
| Rear position light | Find the lights in the manual that make the rear of the vehicle visible within the general lighting arrangement. |
| Brake light | Check the light associated with the braking function and its position as seen from outside. |
| Rear fog light | Learn the control and symbol for the separate function that helps with being noticed from behind in low visibility. |
| Front fog light | If present on the vehicle, evaluate the front-facing function separately from the rear fog light. |
Read the control and indicator together
Once you have found the button for the rear fog light, read the activation conditions in the manual. For example, in the V90 manual, for the relevant function to be available, the vehicle and lighting control must be in specific positions. Do not imitate the button layout or lighting setting of another model. Determine in the manual what conditions are required for your own vehicle. In the initial check, look at when the indicator lights up and what happens when you turn it off with the same control.
If the indicator does not change when you touch the control, check the current lighting position before repeatedly pressing the button. When reading the indicator, distinguish between the front fog light symbol and the rear fog light symbol. The instrument panel lighting or the selected item in the menu does not always indicate by itself that the function you are looking for has been activated. Your vehicle’s manual shows which sign corresponds to the active state.
Verify the off status when visibility improves
Visibility can change throughout a journey. When you pass from a foggy section to a clear area, reassess the condition in which you turned on the rear fog light. When the function is no longer needed, follow the manual to switch it off. Then look at the status of the relevant symbol. A change in lighting setting or turning off the vehicle may automatically terminate the function in some models. Learn in advance how this works on your own vehicle.
When the rear fog light may be used can vary by country. Volvo’s manual also states that usage rules differ by country. In a rental or shared vehicle to be used in another country, learning the vehicle’s controls and checking the applicable rules for the journey are separate preparations. Do not directly take as an example for your own journey the method a driver used in another vehicle.
Quick check that can be done while parked
- Open the rear fog light section in the manual and find the control.
- Verify that the vehicle and exterior lighting are in the position specified in the manual.
- When you turn on the function, look at the correct symbol on the driver display.
- If you need to check the light from outside, do this in a place away from traffic where the vehicle will not move.
- After the off command, verify the off status of the indicator again.
If you are doing the exterior check with someone else, explain in advance what should be seen. Since not all rear lights perform the same function at the same time, the observing person should not confuse normal rear lights with the rear fog light. One person can stay at the vehicle’s controls, the other can compare the off and then on state from a safe point. Do not stand behind the vehicle in a traffic lane or maneuvering area.
If you see a bright light on one side of your own vehicle, do not immediately draw conclusions about the other side. In the V90 manual example, the side where the rear fog light is located is specified. Compare the equipment arrangement with your own vehicle manual. If there is a real discrepancy, tell the service which control was used, what the indicator did, and which light was seen from outside. These observations help distinguish lighting functions that may appear similar at first glance.
A little preparation for a vehicle you will use for the first time
When taking delivery of a vehicle, review the lighting controls. Especially learn from the manual how the rear fog light is turned on together with the automatic headlight option. If the control in the vehicle is accessed via the screen, find the menu while parked and recognize the symbol. Do not expect the same button or menu when you return to your own vehicle. If you regularly use more than one vehicle, it is easier to remember both the steps for turning it on and off separately in each one.
Do not try to tell whether a light is on during a journey solely from the reflection behind the vehicle. Look at the driver indicator you recognized in advance and complete the check in the manual when conditions are appropriate. If you have never used the control before, open the manual at the first suitable safe stop instead of searching for which button it is in heavy traffic. This preparation reduces the need to divert your attention from the road in low visibility.
When you learn the location of the control, take a brief note so you can recognize the symbol in the manual. This note is especially useful if you are using two vehicles with the same body but different lighting equipment. If the indicator layout of one vehicle is different from the other, also review where the symbol appears. Add the switch-off step to your checklist. Instead of assuming that the light will switch off automatically after driving, check the indicator and control as explained in the manual at the moment the use is no longer needed. You can also include this final step in the initial recognition attempt while parked.
Frequently asked questions
Does the rear fog light serve the same function as the brake light?
The brake light is related to braking, the rear fog light to being noticed from behind in low visibility. Check the location and control of both from the vehicle manual.
If I turn on the front fog light, will the rear fog light also turn on?
The control arrangement of the functions is model-specific. Verify the status of the rear fog light with the indicator described for the rear fog.
If the control does not appear active, what is the first check?
Verify the lighting and vehicle state given in the manual. If the same situation repeats under the correct conditions, communicate your observations to service support.
Source: Volvo V90 2024 owner’s manual, rear fog light section.