GMC Dashboard Warning Lights, Symbols, Meaning

Anti-Lock Brake System Fault Indicator

This light means that the anti-lock brake system (ABS) has a problem and has been disabled. 

What this means is that vehicle brakes may lock up under hard braking conditions.

Use a compatible GMC OBD-II ABS scanner to read the codes from the ABS module.

Some of the most common problems that trigger the ABS light on a GMC vehicle:

• Faulty ABS wheel speed sensor
• Broken ABS wheel ring

Service Engine Soon / Check Engine Light

The most common cause of this light is a failure of the onboard emission control system. If this light is on while the engine stays running, it will require an OBD-II scan and diagnostic from a trained GMC technician. Do NOT drive the vehicle if the light is flashing; take the vehicle to be serviced promptly. Pull the vehicle over if the check engine light is flashing and have it towed to a shop.

A flashing indicator is commonly caused by an engine misfire or clogged catalytic converter.

Common causes of the service engine soon malfunction indicator lamp on a GMC vehicle:

• Loose fuel cap
• P0420 catalytic converter failure
• Emission control system failure

Engine Temperature / Overheating

This light means the engine has overheated. Pull over and shut off the engine. Wait at least 30 minutes for the engine to cool down. 

Do not drive with this light on. Continuing to drive if the engine is overheating can lead to serious engine damage, such as a blown head gasket or seized engine. 

Common causes of the engine temperature indicator light on a GMC vehicle:

• Coolant hose, heater core, or radiator leak
• Bad thermostat or cooling fans
• Faulty engine coolant temperature sensor
• Major problems could include a head gasket.
• Water pump failure.

Air Bag Warning Light

This light means that the airbag system has detected a problem. If this light stays on, the airbags may not deploy if you get into an accident. 

To troubleshoot this light, you need to read the fault codes from the airbag module using an Airbag OBD-II Scanner.  

Common problems that trigger the airbag light on a GMC vehicle:

• Dead battery
• Faulty clock spring
• A damaged passenger weight sensor

Tire Pressure Monitor Indicator

When this light comes on with the engine running, one or more of the tires are significantly underinflated. If the light flashes before it stays on, it indicates that one or more of the tire pressure monitor system (TPMS) sensors may be faulty.

Check tire pressures to see if any tire is low on air pressure. If applicable, check the information display for a message indicating which tire is low or faulty. Inflate tires to recommended pressure or take the vehicle to a trained GMC technician to have the TPMS serviced.

Common tire pressure monitor system problems on a GMC vehicle:

• One or more underinflated tires.
• A faulty tire pressure monitor system sensor

Power Steering Light

This light means there is a problem with the power steering. This warning may display as red or yellow. If the steering wheel with the exclamation mark next to it comes on, pull over as soon as it is safe to do so. Turn the wheel to the end of its travel to see if it binds or takes greater effort to steer. Check the power steering fluid reservoir to see if it is low, and listen while turning the wheel for any whining sounds coming from the power steering pump. Take the vehicle to a trained GMC technician to be serviced.

Common power steering system problems on a GMC vehicle:

• In electric power steering equipped vehicles: the power steering motor may be faulty, or a sensor can be defective. 
• In hydraulic power steering vehicles, the power steering reservoir may be low on fluid, the pump seized, or the rack and pinion faulty.

Low Fuel Level 

This light means that vehicle is low on fuel. Find a gas station and add fuel. Check the information display for an estimate on how many miles until the vehicle completely runs out of fuel. It is always a good idea to keep a vehicle from getting low on fuel as this causes the fuel pump to work harder and leads to excess and premature wear.

Common low fuel indicator causes on a GMC vehicle:

• Low fuel
• Faulty fuel pump float

Turn Signal 

The turn signal indicator should flash when the stalk is switched on in either direction. If the light blinks fast, it is an indicator of a bad turn signal bulb. If the light stays on steady when the turn signal stalk is switched on, it is an indication of a bad stalk/switch. Have a GMC technician replace the bad bulbs or faulty switch.

Common turn signal indicator problems on a GMC vehicle:

• Turn signal switch is faulty 
• Burnt out/ bad turn signal bulb

4 Wheel Drive 

This light means that the four-wheel drive has been disabled. The 4WD light will also flash when a problem is detected. A common problem is the 4WD actuator can get rusty and stuck.  

Adaptive Cruise Control

This light means that adaptive cruise control (ACC) has been activated. The vehicle will keep a safe distance from the vehicle in front. If the vehicle in front slows down, your vehicle will slow down as well. If a possible collision is detected, then moderate to heavy braking will be applied, an audible alert will chime, and a visible warning will show on the information display.

Automatic High Beam 

This light means that the high beams will turn on automatically when there is no incoming traffic. The automatic high beam switch needs to be on and the high beams turned on for the automatic high beams to work.

Brake Trouble 

This light means that there is a problem with the brake system. Pull over immediately and check the brake fluid level. Determine whether the brakes are working and if the brake pedal is functioning properly.

Driving with brake system failure is dangerous. Have the vehicle towed to a shop and serviced by a GMC technician. 

Common causes of the brake indicator light on a GMC vehicle:

• Brake system malfunction
• Low brake fluid level
• The parking brake is on (light may illuminate yellow instead of red in this case)

Charge System / Battery Light

If this light comes on while driving, there may be a problem with the electrical charging system. Turn off the engine and check the generator (alternator) belt is in working condition. Do not continue driving if the belt is loose, broken, or missing. Take the vehicle to a mechanic and have the charging system tested.

Common causes of the charging system light on a GMC vehicle:

• Alternator not charging
• Bad battery not holding charge
• Loose battery cable

Cruise Control 

This light means that cruise control has been enabled and is functioning properly. Once a switch or lever sets the cruise control speed, the vehicle will keep constant speed until the brake pedal is pressed. Once the brake pedal is pressed, the cruise control will cancel. The cruise control can be deactivated by the switch/lever, and the indicator will no longer show.

Diesel Exhaust Fluid Warning 

This light means that the diesel exhaust fluid (DEF) level is low, or there is a problem with the diesel particulate filter (DPF). If the DEF is left unfilled, the vehicle will go into limp mode reducing the vehicle’s speed to five miles per hour to prevent any harmful emissions or damage to the DEF system. This light may also come on due to contaminated fluid. It is always important to remain vigilant and check that the DEF is always clean and at an acceptable level when performing routine maintenance.

Common causes of the diesel exhaust fluid warning indicator on a GMC vehicle:

• Low diesel exhaust fluid
• Clogged diesel particulate filter
• Contaminated diesel exhaust fluid

Door Ajar / Door Open

The door ajar indicator stays illuminated when any of the doors or trunks are not closed properly. If this indicator does not go off even after closing the door properly, it may be caused by worn-out latches in the door or a faulty door ajar sensor.

Common causes of the door ajar indicator light on a GMC vehicle:

• Worn-out door latches/ strikers
• Faulty door ajar sensor

Electronic Park Brake Trouble 

This light indicates the parking brake is on. Can illuminate either red or yellow in color. If the parking brake is off, this light indicates the parking brake system needs to be serviced. 

Common causes of the electronic park brake indicator light on a GMC vehicle:

• Park brake module failure
• Improper cable adjustment
• Worn-out/low park brake shoes
• Greater electrical/wiring failure

Fog Lamp 

This light means that the fog lights are turned on. Some vehicles are also equipped with rear fog lights, and an illuminated symbol that is red or amber and pointing to the right will usually indicate the rear fog lights are on.

Forward Alert 

The forward alert indicator warns the driver to let them know a vehicle ahead is approaching too fast or is too close within an acceptable following distance. This warning, both visible and audible, is to help prevent collisions.

Glow Plug 

The glow plug indicator lamp is only equipped on diesel vehicles. A glow plug is meant to warm up an engine block in lower temperatures to ensure proper detonation of diesel fuel since they are internal combustion engines acting without a spark for the detonation of the fuel mixture. In especially cold climates, block heaters are combined with glow plugs to keep a diesel engine from damage and aid in an easier startup.

High Beam 

The high beam indicator turns on when the high beam headlights are activated. Pull the turn signal stalk back to switch between high and low beams. 

Hill Descent and Terrain Mode 

The hill descent and terrain mode indicators mean that a set of electronic systems has been activated that modifies the vehicle’s driving experience. It is an automatic system that changes the functionality of different systems based on the terrain encountered, such as steep hills and snowy, slippery surfaces. It also includes towing, sport, and even Baja and rock crawl modes. 

Systems that may be affected by these modes on a GMC vehicle:

• Power steering
• Stability and traction control
• Throttle and acceleration
• Transmission control
• Locking differential 
• Suspension

Lane Keeping 

The lane-keeping indicator appears when the vehicle is drifting outside of the clearly visible driving lane; it is in. It will gently correct the vehicle back into the center of the lane on equipped models. If the driver engages the steering wheel, the correction will be overridden, and the driver then has full control of the vehicle. Lane indicators (solid and dotted lines) must be clearly visible for this system to engage.

Low Washer Fluid 

This light means that the fluid in the windshield washer reservoir is low. Refer to the owner’s manual for the location of the reservoir. Alternatively, you can look under the hood for a blue cap with the same symbol. Check its level and fill appropriately. 

Oil Warning Light

This light means the oil pressure is outside of acceptable limits. Immediately check the pressure gauge on the dash to see the oil pressure level. Pull the vehicle over and turn the engine off when it is safe to do so. Check the oil level to see if it is low. If the oil level is acceptable and the pressure is still low, this indicates a greater mechanical failure within the engine, such as a failed oil pump, worn piston rings, or blocked oil passages. Have the vehicle towed to a GMC technician to have it diagnosed and serviced. Do NOT drive the vehicle with low oil pressure as it will cause almost immediate and serious damage to the engine.

Common causes of the low oil pressure indicator on a GMC vehicle:

• Bad oil pressure sending sensor
• Failed oil pump
• Worn piston rings
• Blocked oil passages
• Low oil or oil that has turned to sludge from never changing it

Park Brake Light Stays On

If the brake light is on, the brake system may need to be serviced. We do not recommend driving the vehicle with the brake light on. Use your best judgment to determine if the vehicle is safe to drive. If in need of repairs, have the vehicle towed to the shop; driving in this condition could be dangerous.

Common causes of the brake indicator light on a GMC vehicle:

• Brake system malfunction
• Low brake fluid level
• The parking brake is on (light may illuminate yellow instead of red in this case)

Park Lamps ON 

The park lamps indicator shows that the parking lamps are running. Parking lamps were originally intended as a dim light to be left on while the vehicle was parked in situations where there wasn’t much street light. However, that doesn’t apply in modern situations, and no one uses it in that way anymore. The best use of these lamps, and probably the only way they are used today, is in situations where it is not quite dark enough for the headlamps to be on and where the parking lamps would help give visibility to the vehicle without being too bright and distracting like the headlights. 

Pedestrian Warning 

The pedestrian warning indicator comes on when the front-facing camera system detects a possible collision with a pedestrian ahead of the forward-moving vehicle. This visible indicator appears, and an audible chime can be heard. The vehicle automatically brakes when it detects a sudden pedestrian collision to avoid injury. The system is only active between 5-55 miles per hour, and nighttime vision is limited.

Seat Belt Reminder

This is a reminder to fasten the front driver or passenger’s seatbelt. An audible chime can usually be heard, indicating this.

Security 

If the security indicator lamp is still on when the engine is running, there is a problem with the theft-deterrent system on the GMC vehicle. This light comes on when the ignition is off as part of the anti-theft system. This light will flash rapidly while arming if an entry point is not closed properly. This light stays solid as part of the anti-theft system when all the vehicle entry points are closed and locked.

Stability Control On or Flashes

The stability control indicator is part of the StabiliTrak system equipped with GMC vehicles. It is an electronic stability control system that can apply brakes, control engine power, and even steer a vehicle. This indicator only comes on when the system has engaged in a hazardous situation, such as a snowy or wet road where the driver has lost traction and the vehicle begins to slide or spin out of control. It is advised to have traction control in working conditions as it helps to avoid collisions and save lives.

Stability Control OFF 

The stability control off indicator means that the StabiliTrak system on a GMC vehicle has been turned off. Turn the system back on by pressing the traction control switch on the dash. If the light does not go off when the traction control is turned on, the StabiliTrak system is not functioning properly and has been disengaged. In most cases, a message will also appear on the display information in the dash for the StabiliTrak system to be serviced. All systems that the StabiliTrak system uses must be functioning properly for it to work.

Common causes of the stability control (StabiliTrak) failing on a GMC vehicle:

• Faulty steering angle or wheel speed sensors/contaminated sensors
• Faulty ABS system
• Faulty power steering system
• Engine problems such as misfiring cylinders

Tow Mode and Control 

The tow mode and control indicator changes the shift points in the transmission of a GMC vehicle. It helps to protect the transmission by putting it in lower gears that can handle more torque and give the driver the ability to haul heavier loads. When the vehicle is using these lower gears, it also increases engine RPM closer to peak power. This improves engine performance allowing the vehicle to haul big loads easier. It also helps save the brakes when descending hills by shifting the transmission back down at lower points utilizing the transmission as a brake.

Traction Control 

Refer to the stability control indicator above. This system works in exactly the same way but may not include steering correction like the StabiliTrak system.

UpShift Light 

The upshift light indicator comes on at a higher RPM band, indicating that the vehicle needs to be shifted into the next gear. If this light stops working without any other error messages, it is likely a case of simply replacing the bulb in the shifter console.