Check Engine / Service Engine Soon Light Quiz PDF Print E-mail

"Check Engine"/"Service Engine Soon" Light Quiz: Do You Know What to Do If Yours Turns On?

Twenty-five years ago, the only dashboard warning lights you had to worry about were the ominous red “Oil” and “Battery” sirens. Today’s dashboards are a smorgasbord of rainbow colors with indicators for everything from anti-skid controls to airbag circuit warnings.
The most common of these is the amber "Check Engine" or “Service Engine Soon” light, and many consumers aren’t certain what it means or what to do when the light turns on. Here’s a short quiz to help guide you the next time the light brightens your dashscape:
1) If my “Service Engine Soon” light comes on while I’m driving, I should:
    a. Drive immediately to a place where it’s safe to park, shut the vehicle off and call a tow truck.
    b. Continue on my way but seek service as soon as I have a reasonable opportunity.
    c. Disregard it. The light is an overzealous warning system.
Answer: B. The “Service Engine Soon” light is triggered when the vehicle’s computers detect that a component or circuit in the vehicle is no longer operating within specification. The light may sometimes be paired with a drivability problem, such as hesitation, misfiring or stalling. This obviously requires attention sooner rather than later. In other cases, the vehicle will continue to drive normally for a while because the computer system adjusts for the problem, often resulting in lower fuel economy, higher emissions and reduced peak performance.
2) How many components does my vehicle computer monitor that can trigger the “Check Engine” light?
    a. 25
    b. 500
    c. 1,500
Answer: C. All 1996 and newer (and some 1994 and 1995) vehicles are equipped with On-Board Diagnostics II. The job of the OBD-II system is to monitor hundreds of functions within the engine control, powertrain and vehicle body control systems, as well as the communication between them. Any time a problem is detected that could increase emissions levels, the light is illuminated. This is the only way your vehicle can tell you something’s amiss. If you resolve a problem that triggers the light one month and the light returns in six months, it’s not unusual for the cause to be a separate, unrelated issue.
3) True or False: My “Service Engine Soon” light sometimes will turn on and off because of a “computer glitch”.
Answer: False. The vehicle monitoring system is extremely reliable and stable. Before your vehicle’s Engine Control Module (ECM a.k.a. primary computer) triggers the light, it monitors the suspect circuit for a set number of vehicle starts and stops to protect against false alarms.
In some cases, the light may seem to turn on and off at random. This is because the suspect component is performing up to standards at times and then falling below on other occasions. Just as your ECM watches a component before triggering the light, it turns off the light if the suspect part performs as intended for a length of time. Once a faulty part degrades completely, your light will stay on until the part is replaced.
4) True or False: I filled up my gas tank two days ago and now my “Service Engine Soon” light is on. I’ve heard that a loose gas cap can trigger the light. Is this true?
Answer: True. If you have a loose or missing gas cap, fumes from your gas tank are escaping into the atmosphere and your computer detects a leak and increased emissions. On some vehicles, you can properly install the gas cap and the light will turn off. (This may take some time, depending on your driving habits.) Other vehicles require the assistance of a service technician to reset the light. A service technician can confirm the light is on due to a gas cap issue and reset the system at minimal cost. If it is not due to the gas cap, further diagnosis and repair may be necessary.

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