Imagine you are driving happily along and..the dreaded engine light comes on. It is never welcome but it means the computer system in your car has detected a problem. It may be a simple problem to put it right e.g. a fluid level is low, a bulb has failed or it may be more serious like the failure of a component e.g. a sensor or regulator.

The aim of this article is to give you more information so you can decide when you need to get professional help.

For the last 10 years (and for some vehicle makes longer) vehicles have been fitted with Engine management control systems. The ECU (engine control unit) controls not only the engine but also the gearbox (transmission) the brakes and the suspension. The more modern and higher spec. the car the more the features it will have. So there are literally hundreds of reasons for the Engine check light to come on. But don’t panic the ECU can be ‘read’ and a fault code should indicate what the problem is.

What is the Check Engine Light / Engine management light?

All modern vehicles from around 1996 run on engine management systems. And the CEL (check engine light) is a warning light telling you there is a problem; something is not working properly. The malfunction could be a component, or a fluid level or a software problem

Can the car be driven? This is the first question that comes to mind and the general rule is: if the car seems to be running OK you can drive it but you should get it checked as soon as possible. Try to make a decision based on the symptoms – if the car is running rough – stalling, hesitating, driving erratically or seems unsafe in any way best to get it recovered. When in doubt always get it towed!

The CEL went out by itself; is everything OK now? Unfortunately the error may still be present and recorded in the vehicle’s computer system. Again it’s best to get a scan done to sort the problem. To do this you will need a technician with a scanner and the software to do the analysis. A scanner will reveal one or more fault codes and allow the technician to reset the engine check light when the problem has been fixed.

Is there an easy way to clear the code?

Can I disconnect the battery or pull a fuse or disconnect the ECU? Well you know I’m going to say it’s not advisable because it doesn’t solve the problem and the problem will most likely return.

How can I reset the engine light to off?

There is a reason your check light came on and the most likely reason is that there is a fault somewhere in the system. If there is a fault the vehicle’s computer will have stored it as a fault code which, of course, could be any one of hundreds of different codes. Fault codes are fortunately more or less the same across the whole range of different vehicles; that is to say fault code P 0100 is the same for a Jaguar as it is for a Ford as is for an Opel.

The priority is to get the underlying problem fixed. The fault code will either indicate directly where the problem lies, for example a faulty Mass air flow meter (component problem) or it may point to a faulty circuit and more investigation will be needed.The important thing is to get the underlying problem fixed then reset the engine check light. Unless you have scanning equipment yourself you will need the help of a technician. If the problem is simple, an entry level scanner and software will probably solve it. More difficult problems will require more sophisticated equipment. It’s like a medical problem; do you see your doctor or go to a specialist?

We all need expert help from time to time. My advice when looking for expert help is to ask around. Check out other people’s experiences with a particular firm or ask your regular mechanic for advice on who to contact. In addition to all this it’s always best to have as much knowledge yourself on how things work. No one likes a ‘wise guy’ but you’ll be respected for being well informed. For more information on EOBD (electronic on board diagnosis) head over to

By Bethann

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