Engine Light

An illuminated engine warning light means your vehicle has detected a potential emissions fault.The computer has logged one or more diagnostic trouble codes that correspond to the problem and turned on the warning lamp to alert you to the problem.

There is NO way to determine the nature of the problem without connecting a diagnostics computer to the vehicle’s diagnostic connector to read the fault code(s). Once this has been done, further diagnosis and testing may be required to isolate the fault so the correct parts can be replaced.

car20005Depending on the nature of the fault, your engine may not run as good as it normally does, or it may use more fuel than usual. But usually the problem requires attention as soon as it is possible. You can continue to drive your car until it can be diagnosed.

The throttle cable has almost become redundant on today’s motor vehicle. The drive-by-wire system is by no means a new concept as it was introduced by BMW on their 7 series range back in 1988. The system BMW use is referred to as EML (German term for electronic throttle control).

The system has now found its way onto other vehicles with humbler routes and can be found on base models. Historically a mechanical linkage between the accelerator pedal and the throttle butterfly has always existed, be it via a cable or via rods and linkages. These have now been replaced by sophisticated electronic control modules, sensors and actuators. This system is also referred to ‘Fly-by-Wire’.

Common reasons for the CHECK ENGINE light to come on include the failure of an engine sensor such as the oxygen sensor, throttle position sensor or manifold absolute pressure sensor, or a problem in an emissions control system or such as the catalytic converter.

Oxygen sensors, colloquially known as O2 sensors, make modern electronic fuel injection and emission control possible. They determine if the air fuel ratio exiting a gas-combustion engine is rich (with un-burnt fuel vapour) or lean (with excess oxygen). Un-burnt fuel is pollution in the form of air-borne hydrocarbons, while oxides of nitrogen (NOx gases) are a result of excess air in the fuel mixture and cause smog and acid rain.

In practice the oxygen sensor continually signals the ECM to alter the fuelling by a small amount, to maintain the mixture strength as near as possible (+- 1%) to the theoretical ideal (stoichiometric) ratio of 14.7 parts air to 1 part fuel, which is the optimum for the catalytic converter to work efficiently.

A manifold absolute pressure sensor (MAP) is one of the sensors used in an engine’s electronic control system. The manifold absolute pressure sensor provides instantaneous manifold pressure information to the engine’s electronic control unit (ECU). This is necessary to calculate air density and determine the engine’s air mass flow rate, which in turn is used to calculate the appropriate fuel flow.

A crank sensor is a component used to monitor the position or rotational speed of the crankshaft. This information is used by engine management systems to control ignition system timing and other engine parameters. Before electronic crank sensors were available, the distributor would have to be manually adjusted to a timing mark on the engine.

The crank sensor can be used in combination with a similar camshaft position sensor to monitor the relationship between the pistons and valves in the engine, which is particularly important in engines with variable valve timing. It is also commonly the primary source for the measurement of engine speed in revolutions per minute.

Common mounting locations include the main crank pulley, the flywheel, and occasionally on the crankshaft itself. This sensor is the most important sensor in modern day engines. When it fails, there is a small chance the engine will start (engine will likely cut out after a few minutes of driving) but it mostly will not start.

A throttle position sensor (TPS) is a sensor used to monitor the position of the throttle in the engine. The sensor is usually located on the butterfly spindle so that it can directly monitor the position of the butterfly throttle valve.

The sensor is usually a potentiometer and therefore provides a variable resistance dependent upon the position of the butterfly valve (and hence throttles position).

The sensor signal is used by the Engine Control Unit (ECU) as an input to its control system. The ignition timing and fuel injection timing (and potentially other parameters) are altered depending upon the position of the throttle, and also depending on the rate of change of that position. For example, in fuel injected engines, in order to avoid stalling, extra fuel may be injected if the throttle is opened rapidly (mimicking the accelerator pump of carburetor systems).

A catalytic converter is a device used to reduce the toxicity of emissions from the car’s engine. First widely introduced on series-production cars in the US market for the 1975 model year to comply with tightening regulations on auto exhaust, catalytic converters are still most commonly used in motor vehicle exhaust systems. A catalytic converter provides an environment for a chemical reaction wherein toxic combustion by-products are converted to less-toxic substances.

Exhaust gas recirculation (EGR) is a Nox (nitrogen oxide) emissions reduction technique used in most petrol and diesel engines.

EGR works by re-circulating a portion of an engine’s exhaust gas back to the engine cylinders. Intermixing the incoming air with re-circulated exhaust gas dilutes the mix with inert gas, lowering the adiabatic flame temperature and (in diesel engines) reducing the amount of excess oxygen. The exhaust gas also increases the specific heat capacity of the mix lowering the peak combustion temperature. Because NOx formation progresses much faster at high temperatures, EGR serves to limit the generation of NOx.

NOx is primarily formed when a mix of nitrogen and oxygen is subjected to high temperatures.

The engine coolant temperature (ECT) sensor tells the computer what the engine temperature is so that optimum driveability is realised while the engine is warming up and when the engine has reached operating temperature.

In “B.C.” days (Before Computers), cold engine performance was under the control of an automatic choke whose adjustment was critical.

Even when properly adjusted, the engine had to warm up before the car would perform properly. Often the engine had to be run at high rpm at idle just to keep it running when very cold. Then the engine would stumble and hesitate until it got warm. The ECT sensor is critical to many of the engine control unit’s functions such as fuel injection, ignition timing, variable valve timing, and transmission shift.