Your Check Engine Light

Warning Lights and Your Vehicle
by Austin Davis of TrustMyMechanic.com

Reader Question: My check engine light came on the other day what should I do? Will it hurt my car if I continue to drive it?

Dear concerned car owner,

I hear this line at least once a week. The instrument panel on most cars is absolutely cluttered with warning indicator lights and buzzers. These lights are color-coordinated so that different colors indicate the severity of the potential problem. As you start the car, all of the lights should come on, and as the computer verifies each component is working properly, the light is turned off. You should only be concerned with lights that remain on for several minutes after the car has been started.

Treat dash lights like traffic signals. A Red Warning light indicates an immediate danger. Pull over, turn off the car immediately and assess the problem. Symptoms that usually cause red warning lights are engine over-heating, low oil pressure, transmission over-heating, low battery voltage, and brake failure.

Red lights can also indicate a safety issue, so proceed with caution as you maneuver to stop the vehicle. Unfortunately, when the red light is illuminated the problem is at its peek. It can be a matter of seconds before permanent engine damage occurs.

Some common things to look for when a red light comes on are:

low anti-freeze, engine oil, and transmission fluid levels
low brake fluid
missing belts
faulty alternator that is not charging the battery or a bad battery

A Yellow Warning light,indicates "Proceed with caution." The onboard computer system has indicated a potential problem and is alerting the driver. This computer system resets and re-tests all sensors and indicators each time the car is started. The computer system is capable of correcting some minor abnormalities, but if the light continues to come on after multiple car starts, it is probably sensing something that would imply a visit to the diagnostic mechanic is in order.

Some common things that may cause a yellow light to come on, but will probably require an experienced technician to diagnose are:

anti-lock brake systems
safety restraint systems, such as air bags
emissions components
computer-related problems, such as faulty sensors

If you are driving your car and a yellow light comes on, ask yourself these questions:

1. Did you notice problems when starting the car? (slower to start than normal..etc.)

2. Have you noticed a decrease in fuel mileage recently?

3. What is the over-all running condition of the car? Is the engine misfiring or not performing like normal? Are there any new noises from under the hood? Turn off the radio and listen closely as you drive the car.

4. Do you notice any odors, such as a rotten egg smell, or see visible smoke from the tail-pipe or from under the hood?

Make sure to note the exact location and wording of the light that has been coming on, because Murphy's Law dictates that the light will suddenly not come on when you take it in to the repair shop.

In some cars, "engine" is the more serious red light, whereas others use "check engine," which is a yellow caution light. If the mechanic thinks you are seeing a yellow "check engine" light, and your car is indicating a red "engine" danger light, this could be a costly mistake for both of you. Why? You could be having a serious over heating problem and the mechanic is assuming you are having a less serious caution light illuminating. The mechanic then might give you the "green light" (no pun intended) to proceed with your out of town road trip with the kids. Yikes!

Start the car, and point to the light to ensure good communication of the problem. Intermittent dash warning lights can be a pain and hard to diagnose! Diagnosing the problem in some cases will require the light to be on while the mechanic performs the diagnostic test. If the light is not on when you bring the car to the shop, you might be wasting your time and the mechanic's.

SIDE NOTE: Keep a "running condition and dash light" log in your car to help the mechanic pin point the root of the problem. I have a customer who keeps such an accurate log of her cars' complaints that sometimes I can diagnose the problem correctly with the help of her log and by taking her along on my initial test drive. I can do my diagnosis usually without opening the hood to her car. This saves me time and she saves money on a diagnostic charge. This customer can also hold me to my warranty time period, because she had this particular complaint written in her log book.

Sincerely,

Austin C Davis