The 10 Most Common Indicator Lights: What They Mean and What to Do

July 9, 2026

Technical Guide · Indicator Lights · Diagnostics

A light comes on your dashboard. Before panicking or calling the mechanic, here's what each one actually means.

Your dashboard can display dozens of different indicator lights. Some are just informative, others require quick action, and a few mean you need to turn off the engine immediately. Knowing the difference can save you from a major breakdown and, more importantly, an unnecessary mechanic's bill.

The 10 Indicator Lights You Need to Know

Engine Light (Check Engine)

Orange · Urgent

The engine light is the most feared and also the most misunderstood. It can signal dozens of different causes: faulty sensor, injection problem, catalytic converter, EGR valve, lambda sensor. It lights up solid when the fault is stable, and flashes when there are active misfires that could damage the catalytic converter.

What to do: do not ignore. Read the error code with an OBD cable to identify the exact fault before going to the mechanic.

Oil Pressure Light

Red · Critical

This is one of the most serious indicator lights. It indicates that the oil pressure in the engine is insufficient. Continuing to drive with this light on can destroy the engine in a few minutes. Possible causes: lack of oil, faulty oil pump, significant leak.

What to do: turn off the engine immediately. Check the oil level when the engine is cold. If the level is correct, do not restart and call a professional.

Battery / Alternator Light

Red · Critical

This light signals a problem in the electrical charging system. Either the battery is no longer recharging (faulty alternator), or the battery itself is at the end of its life. In both cases, you have little time before the vehicle stops due to lack of electrical power.

What to do: drive to the nearest garage without turning off the engine. Turn off all non-essential equipment. An OBD cable can be used to check the charging voltage in real time.

ABS Light

Orange · Urgent

The ABS (anti-lock braking system) is faulty. In emergency braking, the wheels may lock, which greatly reduces maneuverability. Normal braking remains functional but active safety is compromised. Common causes: faulty wheel sensor, ABS control unit problem.

What to do: read the ABS error code with a compatible OBD cable. A faulty wheel sensor is a simple and inexpensive repair if identified quickly.

Brake Light

Red · Urgent to Critical

This light can indicate several things: the handbrake is engaged, the brake fluid level is low, or there is a fault in the braking system. If the handbrake is fully released and the light remains on, it's serious.

What to do: check the handbrake first. If the light remains on, check the brake fluid level. If in doubt about the brakes, do not drive.

Engine Temperature Light

Red · Critical

The engine is overheating. Possible causes: lack of coolant, stuck thermostat, clogged radiator, faulty water pump. Driving with an overheating engine destroys head gaskets and can crack the engine block.

What to do: turn off the engine immediately as soon as possible. Never open the radiator cap when hot. Let it cool for at least 30 minutes before taking any action.

Tire Pressure Light (TPMS)

Orange · Urgent

One or more tires are underinflated. An improperly inflated tire increases fuel consumption, degrades road holding, and can cause a blowout at high speed. The light can also come on after a significant change in outside temperature.

What to do: check the pressure of each tire as soon as possible. Inflate to the recommended level (indicated on the driver's side door jamb). Some TPMS systems require a reset via an OBD cable after reinflation.

Airbag / SRS Light

Orange · Urgent

The Supplemental Restraint System (airbags, seatbelt pretensioners) has a fault. In the event of a collision, the airbags might not deploy. This light often comes on after a minor collision, a battery replacement, or a connector fault under a seat.

What to do: read the error code with a compatible OBD cable to identify the precise fault. A disconnected connector under a seat is often the cause.

Power Steering Light

Orange · Urgent

The Electric Power Steering (EPS) system has a fault. Steering can become very heavy, especially at low speeds or during maneuvering. The vehicle remains controllable but driving is significantly more difficult and tiring.

What to do: reduce speed and avoid major maneuvers. Read the error code to identify if it's a problem with the steering angle sensor, the EPS control unit, or the electric motor.

Preheating Light (Diesel)

Yellow · Informative

On diesel engines, this light normally comes on when starting in cold weather: you must wait for it to go out before starting. If it remains on after starting or flashes, it indicates a fault with the glow plugs or the fuel supply circuit.

What to do: if the light flashes after starting, read the error codes to identify which glow plug is faulty. Replacement is inexpensive if done quickly.

A light is on? Read the error code yourself.

An OBD cable plugged under the dashboard gives you access to all your car's control units. In a few minutes, you'll know exactly where the problem comes from, without going to the mechanic.

Find my cable in 30 seconds

How to Read Error Codes Yourself

When an indicator light comes on, your car's control unit records an error code (format P0xxx, C0xxx, B0xxx or U0xxx). This code corresponds to a specific fault: sensor, circuit, faulty component.

To read this code, you need an OBD cable adapted to your car and diagnostic software. With the right cable and software like ISTA+, VCDS or Diagbox, anyone can do it from their PC.

A generic cable is not enough A 5-euro ELM327 cable only reads basic engine codes (P0xxx). It does not provide access to ABS, airbag, gearbox or comfort control units. For a complete diagnosis, you need a brand-specific cable.

The GermanConnect configurator gives you the exact cable for your car in 30 seconds, including software and installation assistance.