Top 10 Reasons for an Engine Management Light
Updated: Feb 11
When you engine management light pops up on your dash it can be frustrating and worrying all at the same time. This little light can be responsible for lots of things and often you won't have noticed any change in the way your car is running so can be easy to dismiss. However this little light is there to warn you that something isn't quite right and a trip to the garage is almost always required.
Here at the TOP 10 Reasons this little light might pop up on your dash. What the causes are and what symptoms you may notice as a result.
Top of the list, Mass Airflow Sensor. The airflow sensor does what you might expect, it checks how much air or oxygen is being taken into the engine. too much or too little disrupts the mix of fuel and air to be burned in the engine. You may notice that the car doesn't accelerate smoothly and when idle it will feel rough. There can often be many causes for the air flow to not be measuring correctly, from a faulty sensor or a simple blocked air filter. So don't jump in to the deep end when this code appears and change the sensor as it might not rectify the issue. A good mechanic will look at the data from the engine and determine the reason for the code.
Faulty Oxygen sensor (lambda sensor). We know from the mass air flow sensor how much air is coming into the engine. The oxygen sensor looks at how much oxygen is exiting the car via the exhaust. Most cars will have 2 sensors and a reading between the two will be sent to the on board computer, anything that doesn't add up will cause the light to come on. A diagnostic will determine the issue and location of the faulty sensor and show the data being sent from both. From there we can diagnose and fix the issue and get you on your way.
Faulty EGR Valve (Exhaust gas recirculation valve).This is a critical part for the clean running of your engine. The valve diverts up to 15% of exhaust gasses back into the engine where it is burnt. the most common issue is they can get full of carbon deposits and stick open or shut. Sometimes they can be cleaned so replacement isn't always required. You may notice rough idling and a misfire can often be detected along with difficulty starting.
Leaky Vacuum Hose. Vacuum hoses channel air around the engine ensuring it runs efficiently. They are usually made from rubber and over time can deteriorate, crack, split or break due to being exposed to extremes of temperature. when a variation of the gasses is detected it will be read by a sensor and cause the engine management light to come on. This is usually a fairly easy fix but costs vary depending on the make and model of the vehicle.
Faulty Ignition System. The ignition system is responsible for making sure that fuel and air are ignited at precisely the right time. In a petrol engine its usually the fault of a coil pack or spark plug. In a diesel its likely to be glow plug related but a diagnostic will be required to look at the fault and determine the cause. You will notice if there is an issue with the ignition system as the car will feel rough and often cause a misfire. Being quick to resolve these issues is key to prevent further issues from developing.
Blocked Fuel Injectors. As you would expect a fuel injector injects fuel into the engine. when these become blocked fuel can't get to the engine. Common causes for blocked injectors is from particles not being filtered out by the fuel filter. Check the manufacturers recommended replacement intervals on the fuel filter on your vehicle and get it replaced to prevent this issue.
Blocked Fuel Pump. You guessed it, its the pump that pumps fuel to the injectors under very high pressure. When this becomes blocked it prevents the fuel being delivered to the engine. This can cause the engine to run badly and you may experience issues with starting. The engine management light will come on indicating an issue and you may find your car goes into limp mode to protect the engine. Diagnostics will determine the issue.
Contaminated catalytic converter. The CAT or catalytic converter is responsible for cleaning up the exhaust emissions. The CAT can fail when unburned fuel ignites inside. You may not notice any change in the way your car runs however your MPG may drop considerably so keep an eye on that.
Sooty Particulate Filter. Usually associated with diesel engines. The particulate filter captures the soot created when the fuel and air are burned in the engine. As the filter gets clogged, Vehicles are designed to do a regeneration. This often occurs without you noticing. Under certain parameters the engine will regenerate and remove the soot in the filter. Part of the filter are sensors that measure the pressure inside the filter. If the vehicle is unable to regenerate the engine may go into limp mode to restrict any potential issues. A diagnostic will be able to look at the data, we will be able to see the soot content percentage along with information of the last regeneration to determine the best cause of action.
Loose Filler Cap. When the fuel is pumped out it is replaced with air. This is measured. When the fuel cap is loose it allows too much air in and results in a pressure reading error causing the light to come on. You may notice the light on after a trip to the fuel station so its always worth checking the cap before you panic. A diagnostic will show an issue with the pressure, A good garage will check the cap and send you on your way - You just need to decide who to blame!
As always with cars its never quite as simple as reading a code - the cost of the diagnostic is putting your trust in someone who is able to interpret the information and give you a good diagnosis, not only will this save you money but the outcome will be the one you expect.
As you may have noticed a lot of these issues are preventable, Keeping up with your servicing schedule is vital for prevention of a lot of issues. We recommend servicing your car at least every 12 months or 12,000 miles whichever comes first. Check out our fixed price servicing menu and give us a call for your personal fixed price service.