With almost 60 years in the automotive service industry as a General Motors and ASE Master Technician, automotive technology instructor, and vehicle owner, I know how important properly functioning headlights and high beams are for safeguarding you, your passengers, pedestrians and other drivers’ safety while driving at night.
When it comes to headlights, one might think the biggest worry would be them going out, but another serious problem one might experience is high beams that won’t turn off. This could be dangerous for a few reasons. Besides blinding oncoming traffic, in foggy weather, the bright light from high beams bouncing off the fog can also blind you. It also indicates something’s amiss with your electrical system.
When I first started as a mechanic, “dimmer” switches were simply floor-mounted levers that you pushed to turn the high beams ON and OFF. For safety reasons, by the 1970s, manufacturers replaced the floor-mounted switches with multi-function, steering column-mounted levers (AKA “stalks”) that control headlights, high beams, turn signals, windshield wipers and washers. Today, auto settings that sense when you do and don’t need headlights or high beams and turn them on or off accordingly are very common.
Ahead, an ASE Master Technician and I will explain the most common reasons your high beams won’t shut off.
Reasons Your High Beams Won’t Turn Off
There are several possible reasons your high beams won’t turn off, including:
- Failed or damaged headlight or dimmer switch.
- Misadjusted or loose headlamp lever actuator rod linkage or switch.
- Failed or shorted relay.
- Loose, damaged or corroded wiring.
- Dirty, damaged, or failed automatic headlamp and or high beam sensor.
- Software communication or sync issues between different components.
Depending on your car’s year, make, and model and whether you have the skill and tools to disassemble some tricky assemblies, you may find some simple DIY repairs, while others are dealer-only fixes. Before you begin to troubleshoot the reasons your high beams won’t turn off, check your owner’s manual or service manual to pinpoint where the headlight, high beam dimmer switch, sensors, relays, and fuses are located.
Headlamp or high beam dimmer switch
If a headlamp or high beam dimmer switch is located on the floor, it can be simple to replace. Pull up the carpet and install the new switch.
If the switch is located in the steering column, try using compressed air to clean out any dirt or debris from around the switch level. If you can see the switch wires at the base of the actuator lever, lightly spray with an electrical contact cleaner.
If the switch is located at the bottom of the steering column, spray the actuator with silicone spray (do not use WD-40 o other flammable or harsh chemicals), then move the lever back and forth to lube the switch and actuator.
If the steering column headlamp/dimmer switch needs replacing, it’s best left to the pros.
Headlamp lever actuator rod linkage
On many cars, the dimmer switch is located at the base of the steering column. When you pull back on the lever, a rod (or linkage) activates the switch on and off. After a few years, said ASE Master Technician Joe Simes, “the [dimmer] switch can become loose, or the [actuator] rod may come out of adjustment.”
Many years ago, something similar happened to me. A loose ignition switch at the bottom of the steering column was keeping my vehicle on, draining the battery. Simes explained that “loosening the dimmer switch mounting screws at the bottom of the steering column and adjusting the switch position [and spraying with silicone spray] is something any DIYer should be able to do. But he warned, “leave this to the pros if any SRS (Supplemental Restraint Systems—airbags) components are involved or need disassembly.”
Relays
Relays permit a small amount of current to control a larger, second high-current circuit. When you turn on a switch (the input circuit), a small amount of current activates a coil or electromagnet inside the relay. This closes the relay’s contacts, allowing a much bigger current to flow (output—from a high-current second circuit) to a high-current device, such as high beams. This allows manufacturers to install smaller gauge wires inside the car and steering column.
Stuck or corroded contacts or coil can keep your high beams from turning off. Use your owner’s manual to identify and try replacing the headlight or high beam relay.
Wiring problems
Wiring can cause all kinds of headaches inside a car. Loose or corroded wire connectors and switch contacts due to moisture and road salts, short circuits, wires chaffed inside the steering column, or poor grounds can play all kinds of havoc with your high beams.
Many wiring repairs are DIY. If a device is not working properly, disengage and separate the suspect connector and inspect the terminals to determine if they have backed out of the connector, are bent, damaged or corroded. Clean corroded terminals with electrical contact cleaner. Or repair wires using crimp connectors. Loosen or remove ground cables where they connect to the body. Use a wire brush to thoroughly clean the connector and body panel, then firmly retighten the ground cables. Use a DVOM to check the suspicious connections for voltage drop. If none of this works, it’s time to visit your mechanic.
Automatic high beam sensor and cameras
Automatic dimming high beam systems have been around since the 1950s and are often the most overlooked problem of headlight and high beam malfunctions. “Many modern cars have two automatic high beam sensors and or cameras that are components of ADAS (advanced driver-assistance systems),” said Simes. Sensors or cameras are usually [located] on the top of the dashboard or rearview mirror, the other near the front grille,” added Simes.
Check your owner’s manual to locate camera or sensor locations and make sure they are not covered by dirt or debris. Simes added, “Thoroughly clean the sensors and camera lenses [with a clean microfiber towel] so they can detect daylight, streetlights or headlights from oncoming cars.” He added “use caution when cleaning any lenses. Refer to [your] owner’s manual for any special cleaning procedures, or you may damage them.”
Software and electronic communication issues
“Modern cars use a ‘BUS’ (Binary Unit System) to ensure individual devices [like sensors, actuators, switches, relays, controllers] can quickly exchange data,” says Simes. This greatly improves vehicle systems management, operations, and safety.
Sometimes these extremely complex systems get out of sync—causing the high beams to not turn off—calling for a system restart.
BEWARE: A BUS sync issue (Simes called it a “handshake”) can also cause ADAS system errors, drivability and false trouble code issues. Some manufacturers use a button on the infotainment touch screen you hold down for “X” seconds, or a combination of buttons, holding the high beam lever in the “on” potion for “X” seconds or powering the ignition off and then on “X” number of times. Again, it is important to check your owner’s manual for specific instructions for your year, make and model car.
Below are generic steps you can try to “reboot” the system. PRO TIP: If you’re not completely confident following these steps, take it to your dealer’s service department or mechanic to resync the high beam system.
- Fully discharge the electrical system by disconnecting it for 15 minutes. NOTE: Disconnecting the battery can cause the loss of saved radio station presets, clock, seat position and other custom settings.
- Reconnect the negative battery (-) cable.
- Start the engine and let it idle for five minutes to help the BUS recalibrate.
- Use a scan tool to check and clear trouble codes.
- You may need to drive your car to reset the engine monitors.
The Expert
Joe Simes has spent over 20 years as an ASE and Toyota Master Technician. He is a certified Pennsylvania Department of Education automotive technology instructor, preparing the next generation of automotive service professionals at North Montco Technical Career Center in Lansdale PA., as well as a PA certified emissions and safety inspection instructor and inspector. Email interview Mar 19, 2024.
Resources
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