• 2019

Out of the Fog

Keeping Headlamps From Fogging Up

Gone are the days of the large headlamp bulbs that plugged into a socket in a wire assembly. Today, the headlamp assembly is a molded part into which a small bulb is fitted and locked in place.

While this is more of an aesthetic issue than anything else, it still must be addressed and corrected. Failure to do so can lead to a diffused headlamp light beam.

Inside the lamp assembly is an empty void filled with air. The back surface has a reflective coating and the front face is the lens through which the light escapes. The fogging issue can arise from the air inside this void.

Headlamp Fogging

Very simply, the fogging is caused by water vapor condensing inside the lamp assembly. This vapor usually collects on the inside surface of the lens. The phenomenon is similar to the inside surface of the windshield fogging, which requires the use of the defroster to clear the windshield. It’s all based on temperature and relative humidity.

Warm air holds more moisture than cold air, which explains the cause of natural fog — the temperature of humid air cooling rapidly. The result is the condensation of the water vapor. This is what is occurring inside that empty area of the headlamp assembly. Fogging doesn’t happen on every truck, however. On trucks in which it does occur, it doesn’t happen all the time. It depends on the condition of the atmosphere — temperature and humidity.

Your customers might report that, on occasion, the in-lamp assemblies are fogged with a light layer of condensation on the inside of the lens. In some cases, this is seen after the lamps have been turned on, brought up to operating temperature (headlamp bulbs are hot), turned off and then rapidly cooled by cold water from rain or from a car wash.

In other cases, the lens fogging can occur under certain atmospheric conditions. Like when the vehicle has been parked outside overnight. Perhaps, during the day, the temperature was relatively warm and the air was humid, then the temperature dropped significantly at night, which can occur when the sky is clear.

In both of these examples, the fogging disappears when the atmospheric conditions change, allowing the condensation to change back to a vapor. With the rain/car wash scenario, turning the headlamps on heats the air inside the headlamp assembly, allowing the air to hold more moisture. With the truck parked outside, the warming of the day will heat the air inside the assembly, dissipating the fog.

Evaluate the Fogging Condition

There are several Technical Service Bulletins (TSBs) that address headlamp assembly fogging. Two of these are specific to 2012 Ram pickup trucks, number 23-015-18 and number 08-091-14. According to these bulletins, one of two conditions exists — (1) natural fogging due to atmospheric conditions and (2) condensation and water buildup due to sealing problems with the headlamp assembly.

When the fogging condition exists, park the truck in a warm service bay with relatively low humidity. Dry the outside of the headlamp assembly of any water or moisture that might be present. Turn the headlamp high beams on and keep the lights on for 20 minutes.

If the condensation/fogging begins to clear from the lamp lens after this 20-minute time period, the headlamp assembly seal is not defective/damaged. The headlamp assembly does not require replacement. If the condensation/fogging does not dissipate after 20 minutes, there is a problem with the headlamp
assembly seal and the assembly must be replaced.

Figure 1 – Updated vent caps

Correcting the Fogging Condition

If it has been determined that the headlamp assembly seal is not defective/damaged, under the right conditions, fogging can occur again. To prevent re-occurrence of fogging on 2012 Ram pickup truck headlamp assemblies, special vent caps have been designed (see Figure 1). These small caps come in a pack of three, part no. 68353620AA. Two kits are needed per vehicle, one for each headlamp assembly. Each kit will include the updated (brown) vent caps.

If one headlamp assembly has cleared up, but the other one still has heavy condensation in it, only install the vent caps on the assembly that has cleared up. The other assembly must be replaced. When a replacement headlamp assembly is purchased, that new unit will have the updated vent caps installed.

The most difficult task in replacing the vent caps is removing the headlamp assembly from the truck. This must be done in order to access the vent caps. Let’s review the removal and installation procedures for a headlamp assembly on a typical Ram pickup. For our example, we are using a 2014 Ram 1500 as the subject vehicle. Check the service procedures for the specific vehicle being serviced.

Figure 2 – Updated vent caps in place

First, remove the four plastic push-in fasteners that secure the upper radiator seal to the grille support and both fender ledges. Then, remove the two plastic push-pin rivets that secure the upper radiator seal to the radiator. Remove the upper radiator seal from the vehicle.

Note: It is not necessary to remove the grille to remove the front headlamp units.

Remove the screw that secures the upper mounting tab of the front lamp unit to the Front End Module (FEM) carrier. Using a socket with a magnetic insert, reach down between the grille and the FEM carrier to access, remove and retrieve the screw that secures the lower mounting tab of the front lamp unit.

Remove the fastener that secures the tab at the bottom of the access panel to the front of the front wheel house splash shield. Reach through the access opening of the wheel house splash shield and lift the slide lock upward far enough to disengage it from the lock post integral to the back of the front lamp unit housing.

From the front of the vehicle, grasp the outboard edge of the front lamp unit firmly and pull it straight forward to disengage the ball stud from the plastic grommet in the FEM carrier. Pull the lamp away from the front of the vehicle far enough to access and disconnect the two wire harness connections from the assembly. Remove the front lamp unit from the vehicle.

With the headlamp assembly on the workbench, replace the vent caps with the new, brown caps from the repair kit (see Figure 2). Note that this headlamp assembly has only two vents. Most models have three vents. Install the headlamp assembly in the reverse order it was removed to complete the repair task. Then you’ll be seeing things clearer.