Blinking Check Engine Light Explained

There is a huge difference between driving your vehicle with the check engine light on solid and driving your vehicle with the check engine light blinking.

"Can I drive my vehicle with the check engine light flashing?" My strong suggestion is to only drive your vehicle long enough to get to a safe place to stop.  If you are driving down the freeway and your check engine light starts flashing, safely make your way to the shoulder and call for roadside assistance. Your vehicle's engine light is designed to flash when it is detecting a major misfire. Driving your vehicle for an extended time with a major misfire will likely cause damage to the engine itself or more commonly the catalytic convertor. So although your vehicle will likely remain running and get you back home, I strongly suggest pulling over once safe and calling for a tow truck to avoid damaging any components that may still be good. In the end, the cost of the tow will likely be much less than the repairs needed to repair any extra components damaged by driving too far with the engine light flashing.


"Can I drive my vehicle with the check engine light on?" There typically is not much risk to drive your vehicle a short amount of time with the check engine light on solid. By "short amount of time". I mean, finish your way home from work or finish running your errands. There are some cases where you could save yourself the risk of a breakdown or a more expensive repair to get your vehicle checked out sooner rather than later once the light comes on.  Your check engine light can come on for many different reasons. Your vehicle's onboard computer is constantly monitoring several systems on your vehicle as you are driving. Emissions system like the catalyst system, exhaust gas recirculation system, and the evaporative system. Engine performance systems like the fuel system and oxygen sensors. It is even monitoring for ignition misfires while driving. Once your onboard computer detects a problem, it will illuminate the check engine light. Once this happens, the computer stores a code pertaining to what system is not within specification and points you in a certain direction to diagnose the problem.  Auto repair mechanics utilize these codes to know what system is acting up and a general idea of what components need to be checked to determine the exact cause. If you are mechanically inclined, retrieve the codes, print out the recommended diagnostic strategy, and get to testing. If you do not prefer to work on your own vehicle, call your trusted mechanic and get on their schedule for diagnostic testing.

                                                     Check Engine Light Code Reader 

What is causing your check engine light?

Any time your vehicle's onboard computer detects a fault in one of the monitored systems, it stores a trouble code that helps in diagnosing. These trouble codes are easily retrieved with a code reader or scan tool. Most auto repair shops have them and a lot of parts stores have them as well. My warning is simply to be careful if utilizing the free code scan service offered by most parts stores. Trouble codes simply point a mechanic in the direction of what system needs proper testing rather than pinpointing the exact problem. As an auto repair shop owner, I see too many times a do-it-yourself or parts store jumps to conclusions and sells the vehicle owner parts that don’t actually fix the problem.

Here are a few examples of trouble codes and common causes.

P0300- Multiple Misfire-  This trouble code shows that your computer detected a misfire on one cylinder or more.  The most common cause is a worn tune-up part like a spark plug or spark plug wire.  Just because that is a common cause doesn’t mean that is what your vehicle needs.  There are dozens of other things that need to be tested before moving forward and spending money on parts.

P0420- Catalyst Efficiency below threshold- This a trouble code commonly seen when your vehicle catalytic converter is failing.  This is a very expensive part to replace and this code can be caused by several other things like exhaust leaks and sensor failures.  Please don’t jump to conclusions and replace this expensive component without properly diagnosing first.

P0442- Evaporative system leak- EVAP systems can be very technical to diagnose.  It can also be as simple as a loose or failing gas cap.  Always check this first.  My auto repair shops often utilize a factory scan tool and a smoke machine to properly diagnose this system.  Can be a faulty component or a leak somewhere in the system.

P0171- Fuel system lean- This code tells us that your air/fuel mixture is incorrect. Common causes are vacuum leaks, fuel system problems or sensor problems. Don’t jump to conclusions when this code is found. It can be caused by a number of things.