Automobile Repair/Warning light system

The instrument cluster uses a set of standardised symbols to report the state of the car's systems. Most of them light briefly when the ignition is switched on, as a bulb and circuit check, and go out a few seconds after the engine starts. A symbol that stays on, or comes on while driving, is a message. The colour tells you how urgent it is: Red: stop as soon as it is safe to do so. Red lights report conditions that can damage the engine or make the car unsafe to drive (oil pressure, coolant temperature, brake system, charging system). Amber or yellow: a fault or a reduced function; the car can usually be driven to a workshop (engine management, ABS, tyre pressure, traction control, driver-assistance systems). Green or blue: information only (headlamps, indicators, cruise control engaged). The exact symbols, their colours and the manufacturer's advice are in the owner's manual, which is the authority for any given car. The sections below describe the most common lights. Brake system warning light left|frameless|Brake system warning Cause: The light comes on when the parking brake is applied, when the brake fluid in the reservoir has dropped to the MIN mark, or, on many cars, when the brake pads have worn to their wear sensors. Actions: If the light stays on after the parking brake is released, check the brake fluid level. A low level usually means worn pads (the fluid has moved into the calipers to take up the pad wear) or a leak. Top up only with the specified fluid, and look for the cause. If the pedal feels soft or travels further than usual, do not drive the car; braking effort and stopping distance will both be affected. Note 1: When this light and the ABS warning light are on together, the anti-lock braking system may have a fault that also affects normal braking, and the car may become unstable under hard braking. Stop in a safe place and have the car recovered rather than driven. Note 2: A continuous squeal or a grinding noise under braking usually means the pads are worn to the backing plate. Have the brakes inspected before driving further. Battery charging warning light left|frameless|Charging system warning Cause: The charging system is not producing voltage with the engine running. The usual causes are a broken or slipping drive belt, a failed alternator, or a fault in the wiring between the alternator and the battery. Actions: Switch off every accessory you can (air conditioning, heated seats, audio, phone charging) to reduce the drain on the battery, and drive to the nearest workshop. With no charging the car runs on the battery alone, and a modern car with electric power steering and fuel injection may stop within a short distance once the battery is exhausted. Check the drive belt first: with the engine off, look for a missing, broken or loose belt. If the belt is intact, measure the battery voltage with the engine running; a healthy charging system shows roughly 13.5 to 14.8 volts at the battery terminals, while a reading at or below the resting voltage (about 12.6 volts) confirms that the alternator is not charging. Note 1: On most engines the same belt drives the water pump. If the belt has broken, do not continue driving: the engine will overheat within minutes. Note 2: A battery that will not hold a charge after the alternator has been checked and found good is normally at the end of its life. Anti-lock braking system (ABS) warning light left|frameless|Anti-lock braking system symbolCause: The ABS control module has detected a fault. The common causes are a wheel speed sensor that has failed or whose tone ring is dirty or damaged, a blown fuse, a low system voltage, or a fault in the hydraulic modulator. Note 1: If the ABS warning light and the brake system warning light are on together, braking performance may be seriously reduced. Stop the car in a safe place. Actions: The ABS light alone does not mean the brakes have failed: normal braking remains available but the wheels can lock under hard braking and the stability control is usually disabled at the same time. Have the fault codes read. Wheel speed sensor faults are reported by wheel position, which makes the repair straightforward. Note 2: The ABS performs a self-test each time the ignition is switched on and again when the car first moves. The light comes on during the test and goes out when the test passes. Note 3: A light that comes on while driving means the ABS has switched itself off. Allow more distance and brake more gently until the fault is repaired. Malfunction indicator light (check engine light) left|frameless Cause: The engine control module has stored a fault code. The light is required by emissions regulations and covers anything that can raise emissions: a misfire, a fuel mixture out of range, a failed oxygen sensor, a leak in the evaporative emissions system (including a loose fuel cap), or a sensor circuit fault. Note 1: A steady light means a fault is stored and the car can normally be driven to a workshop. A flashing light means a misfire severe enough to damage the catalytic converter; reduce speed and load and have the car checked immediately. Actions: (i) Check that the fuel filler cap is tight. A loose cap sets an evaporative system code on many cars; the light goes out by itself after several drive cycles once the cap is tightened. (ii) Read the fault code with an OBD-II scan tool. Every car sold in the United States since 1996 (and in the European Union since 2001 for petrol and 2004 for diesel) has a standard diagnostic connector, usually under the dashboard on the driver's side. The code (for example P0301, cylinder 1 misfire) identifies the system at fault and is the starting point for any repair. Note 2: Driving for weeks with the light on risks turning a cheap repair (a sensor or a cap) into an expensive one (a catalytic converter). Oil pressure warning light Cause: The oil pressure in the engine has fallen below the switch's threshold. Causes include a low oil level, a failed oil pump, a worn engine, or a faulty pressure switch. Actions: Stop the engine as soon as it is safe to do so. Check the oil level and top up if it is low. If the level is correct and the light stays on, do not run the engine; have the car recovered. An engine run without oil pressure can be destroyed in less than a minute. Coolant temperature warning light Cause: The coolant temperature is above the normal range, usually because of a low coolant level, a failed thermostat, a cooling fan that is not running, or a failed water pump. Actions: Switch the air conditioning off and the heater on full to shed heat, and stop in a safe place if the light stays on. Do not open the cooling system while it is hot. See the chapter on the cooling system. Tyre pressure monitoring (TPMS) light Cause: One or more tyres is below the pressure set in the system, or (when the light flashes for about a minute at start-up and then stays on) the monitoring system itself has a fault, often a sensor with a flat battery. Actions: Check all tyre pressures with a gauge, including the spare if it carries a sensor, and inflate to the pressure on the door-frame placard. The light normally goes out after a few minutes of driving. See Tire pressure. Airbag (SRS) warning light Cause: The restraint system control module has stored a fault: a seat-belt pretensioner, an airbag connector (often under a seat), an occupant sensor, or the module itself. Actions: The airbags may not deploy in a collision while the light is on. Have the fault codes read. This system is not a DIY repair. Driver-assistance system warnings Cars with forward-collision warning, automatic braking, lane keeping or adaptive cruise control show their own messages when a camera or radar is blocked, misaligned or faulty. See the chapter on "smart" car systems. References https://repairpal.com/warning-lights-chart