Dear Car Guy:
My “Check Engine” light keeps going on after I’ve been driving for a while. I don’t have the slightest idea why or what it means. When I start the car, everything is fine, but then the light goes on. Any ideas?
Thanks,
Paul Ocean
Dear Paul,
Before “talking” GPS systems and those incredibly annoying “fasten your seat belt” chimes, there was the “Check Engine” light. I’d bet that 90% of drivers ignore the “Check Engine” light, and a fair portion of the other 10% stop the car, open the hood and check to make sure the engine is still there! Everybody is confused about the “Check Engine” light, so let me try to clear things up for you.
The “Check Engine” light, usually a yellow or light orange color when lit, began its fabled existence around 1982, designated as OBD-I (on-board diagnostics.1, supplanted by OBD-II around 1996). Essentially, it was created to monitor emissions control, and to notify the driver if one of a number of sensors detected conditions that were “out of specifications.” In plain English, this means detecting things like improper air density volume, pressure, and fuel mixture. Any one of these conditions can create increased pollution, and the “Check Engine” light indicates that fuel is not being burned by the engine properly. In other words, Paul, if the light is on you’re wasting gas and it’s costing you money.
Now some people think that when the “Check Engine” light goes on, their car is about to explode and they need to pull over, but it’s not about that. The car is not going to blow-up or catch on fire. But, there may in fact be something seriously wrong with the car, and it needs to be researched and fixed. If the “Check Engine” light does not go on for a while when driving and then goes on, please pay attention. Chances are that a cooler engine is delaying the detection of a problem. So while you can continue to drive your car when the “Check Engine” light goes on, it’s always worth investigating.
When investigated, the cause occasionally is the failure of a sensor itself. Like any automotive part, sensors can fail and need to be replaced. There may be nothing else wrong with the car, but if the sensor is not working it cannot detect problems if they arise. The beauty of computers, (and the OBD-II is connected to your on-board computer) is that they compile a complete history that can be downloaded and reviewed. Don’t worry Paul, this diagnostic history tool will not record that secret Double Whopper with bacon and cheese that you gulped down on your way home, but it will allow a mechanic to correctly ascertain the reason that the “Check Engine” light went on.
There are some dashboard lights you absolutely, positively need to notice, and when you do, pull over, stop the car and turn off the engine. If your “Check Oil” light goes on, and it’s always RED in color, it indicates that your oil level has dropped dangerously low. When this light comes on – I repeat – pull over! You can ignore the “Check Engine” light, but ignoring the “Check Oil” light risks burning out your engine and a big repair job. Same goes for the “Check Brakes” light; if that light goes on it means your car’s brake fluid level has dropped too low, and your braking system may not work properly. If your “Check Coolant Level” light goes on, you probably have a leak in your coolant line, and your car can overheat.
Nowadays, there are many dashboard lights built into cars, and if you review your auto information booklet (yes Paul, the one that’s buried under the old maps, hair brushes and soiled Double Whopper wrappers in your glove compartment) you can find out what each and everyone is and what it means. The rule of thumb is YELLOW means CAUTION (no danger but something is out-of-whack) and RED means DANGER (stop driving, pull over and call a tow-truck).
I have a customer who brought her car in for a tune-up because she thought she was not getting very good gas mileage. When I started the car, I noticed that a piece of paper was taped over the “Check Engine” light, which was lit. “It was too annoying to look at every day,” she said. Go figure!
The Car Guy, John Fisher, owns and operates Metric Motors Auto Repair here in Sonoma Valley, and has been fixing cars for close to 30 years.
