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The Idiot’s Guide To Idiot Lights

Posted in Car Care, Car Tech, Cars, driving, Featured, General, Guide, Maintenance, Promoted, Repair by Kurt Ernst | December 14th, 2010 | 10 Responses |

Back in the stone ages of motoring, cars came with real instrumentation, typically including a tachometer (to measure engine speed), a speedometer (to measure road speed), a voltage gauge or an ammeter (to measure voltage or current to the battery), an oil pressure gauge, an oil temperature gauge, fuel gauge and a coolant temperature gauge. Over the years, car makers realized two things: it was cheaper to replace functional gauges with idiot lights, and people actually paid more attention to idiot lights than they did gauges. Thus was born the modern instrument panel, which now typically includes a speedometer, a fuel gauge and (maybe) a temperature gauge and tachometer. All of the other critical information your car can display to you is now done via the driver information display or via idiot lights.

When a dash warning light comes on, it always signals trouble. Sometimes this is serious, pull to the side of the road NOW stuff, while other times it’s get-around-to-having-it-looked-at-next-week stuff. If you’re reading car blogs, chances are good you already know this; however, you’d be surprised at the number of drivers who have no clue what a particular warning light indicates. Below I’ll try to give you an example of the more common ones, along with my take on how serious the situation is. If you remember nothing else, remember this: automakers typically code warning lights either red or yellow. If you see a red light, it’s a good idea to pull to the side of the road as quick as you can safely do so. A yellow light typically signifies a problem as well, but one you can address after you get home.

Red Warning Lights

Oil Pressure

Typically represented by a stylized oil can, this is the mother of all warning lights. If you see the low oil pressure light come on, stop the car as soon as you safely can. Most oil pressure warning lights don’t even trip until the engine is already being damaged, so if this light comes on don’t even think about driving the car until you check and replenish the lost oil.

Coolant Temperature

Typically represented by the word “TEMP” or a stylized thermometer, this is another warning light that demands your immediate attention. You car will soon begin to overheat, if it isn’t doing so already, probably because your engine coolant level is low. Stop the car as soon as you can safely do so and check the coolant level in the external reservoir. DO NOT attempt to open the radiator cap, unless a face full of steam and scalding water is your idea of a good time.


Typically represented by the word “BRAKE”, this usually means one of two things: either you forgot to release the parking brake and are enjoying the smell of burning brake pads, or your brake fluid level is low. On a modern vehicle, that’s a pretty unusual situation unless your brake pads are completely worn out or you’ve got a leak in your hydraulic system. If it were me, I’d limp the car home but give myself more braking distance since I’d expect pedal effort to increase as I continued to drive. If you’re not comfortable driving with reduced braking ability, I’d seriously encourage you to pull to the side of the road and have your car towed.


Typically represented by a battery symbol, this means your charging system isn’t working properly. It may also mean you’re living on borrowed time, as your car will be drawing down the voltage in your battery without replenishing it. If your close to home (less than 30 minutes) and you’ve got a battery less than 3 years old, go for it. If you’re hours away from home and the battery is ancient, you won’t be going too far.

Yellow Warning Lights

Check Engine

Typically represented by a stylized engine, this light signals that you’ve got some kind of trouble with your engine’s emission control systems. It may be as simple as a loose gas cap, or as complicated as a defective oxygen sensor. Most modern cars have a “limp home” mode that allow you to drive at reduced power; in a worst case scenario, you’ll just take longer getting home than planned. Get this checked out as soon as you can, but don’t let it stop you from driving home.

Tire Pressure

Usually represented by a cross section of tire with an exclamation point in the center, this light means that one of your tires is low. Some newer cars have an information display that will tell you which tire is low. Less well-equipped vehicles (like my FJ Cruiser) require you to check each tire to find the one down on pressure. If I were behind the wheel, I’d stop and check my tire pressure as soon as possible, starting with my spare tire (assuming you have a full size spare equipped with a pressure sensor). Since I carry a plug repair kit and compressor with me, I’d inspect the low pressure tire for punctures, repair, re-inflate and be on my way.

Traction / Stability Control

Typically, this light shows a car with skid marks behind it. If the light is on, your stability control isn’t working: verify that you haven’t turned the system off by accident, and proceed with caution.

ABS System

Represented by the letters “ABS” in a circle surrounded by brackets, this light means that your ABS system isn’t working as intended. It may be something as simple as a blocked sensor, or it may mean mechanical damage to the ABS system itself. I’ve driven a lot of cars without ABS, so this wouldn’t cause me much concern; as long as the red “Brake” light isn’t on, you should have reasonable braking ability (though without the anti-lock feature).

Remember that this is a general summary, and that your car and circumstances may vary. When in doubt about your car’s safety (or your ability to drive a damaged car) always err on the side of caution and pull over when it’s safe to do so.

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10 Responses

  1. Lee says:

    My Volvo S80 has a Lambda that lights up and it isn’t in the owners manual, any ideas what that would mean?

  2. Kurt Ernst says:

    Lee, what year S80 is it? You say it’s a “lambda”, so I assume it looks like the Greek letter L – correct? What other warning lights surround it?

    With nothing else to go on, my first guess is that it’s for a faulty oxygen sensor. If you can give me more info, I’ll see what I can find out.

  3. a says:

    my town car has the oil pressure light just about every time i start it up in cold weather, like today, but it’s gone after the car warms up. should i still add oil every week or so?

  4. Kurt Ernst says:

    a, chances are good it’s low on oil, and develops just enough oil pressure when the car is warm to turn out the light. When was the last time you checked the oil level on the dipstick?

    Keeping oil in the car is as essential as keeping gas in the car. The difference is, running out of gas leaves you stranded temporarily; running out of oil leaves you stranded until you replace the engine.

  5. Taylor says:

    The TPMS, while acting as a good reminder for people to check their tire pressure, is in my opinion more of a CYA tool for auto and tire manufacturers stemming from the whole Explorer rollover thing.

    The sensors are finicky enough to be triggered by temperature and elevation changes so it becomes a “boy who cried wolf” situation after enough times.

    For example, say you adjust your cold (should always be measured cold) air pressure to adjust for a cold ambient temperature and high altitude (6500 ft) so that you are running 35 psi. Now you take a trip that takes you to warmer climates and lower altitude (1200 ft). You now have the combined effects of temperature and altitude pushing the pressure in your tires above the 35 psi into an overpressure state, which is harmful and/or dangerous in its own right.

    And before someone says that the pressure differences created by temp and/or altitude are insignificant I would like to point out that the TPMS light on my personal vehicle have lit consistantly in various situations where the only direct factor is temp or altitude. If either of these were insignificant the TPMS would not light.

  6. Kurt Ernst says:

    Taylor, you’re absolutely correct about TPMS systems being finicky, but I still think they’re a great advantage for the non-enthusiast. Let’s face it: most people rarely (if ever) check their tire pressure, so anything that prompts them to do so is a good thing.

    Another interesting result of the Explorer rollover crisis is the redesign of the new Explorer – it’s much more “car like” than any of its predecessors, but still has surprising off-road capability. Behind the wheel, it feels like a big sedan, which is what the vast majority of buyers want.

  7. Lee says:

    Yes you have the right lambda, it is a 1999 S80 and the light is only on sometimes. Thanks for the help.

  8. Kurt Ernst says:

    Lee, I couldn’t find anything specific to your issue on the internet, and since I’m not a Volvo guy myself this is just an educated guess. I’m assuming the light with the “lambda” symbol is yellow, correct? An oxygen sensor is also called a “lambda sensor”, so I suspect you have a bad oxygen sensor, specifically the one mounted at the entry to your catalytic converter. There’s good news and bad news on this: the part itself (assuming that’s truly what’s wrong) is relatively inexpensive, about $50 or $60. If you’re mechanically inclined and have access to a set of ramps, you should be able to change it yourself. Now the bad news: you should also have a warning message that reads “Service Engine” or something like it. Resetting this requires access to a specific Volvo tool, which requires (you guessed it) a trip to your Volvo dealer. As far as I know, you can’t reset the code with a standard OBDII reader or tool.

    I’d suggest you take it to a Volvo dealer (or independent shop who specializes in Volvo repairs) and have them diagnose it. If it’s the lambda sensor, get a quote on repair since there shouldn’t be much labor involved.

    You definitely want to get this looked at, since a bad oxygen sensor will cause the car to run rich. That costs you more in gas and reduces performance, not to mention wearing out your catalytic converter a lot sooner.

  9. Lee says:

    Thanks so much for the help. I have a good independent shop to check it out.

  10. […] The Idiot's Guide To Idiot Lights Over the years, car makers realized two things: it was cheaper to replace functional gauges with idiot lights, and people actually paid more attention to idiot lights than they did gauges. Thus was born the modern instrument panel, […]