All modern vehicles have a computer or ECU (Electronic Control Unit) that controls engine operation. The main purpose of this is to keep the engine running at top efficiency with the lowest possible emissions. With today's strictest emission regulations it's not very easy to achieve.

The engine needs to be constantly and precisely adjusted according to various conditions such as speed, load, engine temperature, fuel quality, ambient air
temperature, road conditions, etc.

There are a number of sensors that provide the ECU with all necessary inputs such as the engine temperature, ambient temperature, vehicle speed, load, etc.
According to these inputs, the ECU makes initial adjustments adding or subtracting fuel, advancing or retarding the ignition timing, increasing or decreasing idle speed, etc.

Below is a small list of those sensors and the role they play. There is a primary oxygen sensor installed in the exhaust before the catalytic converter that monitors the quality of combustion in the cylinders. Based on the feedback from this oxygen sensor the ECU makes fine adjustment to the air-fuel mixture to further reduce emissions.

On some vehicles there can be another secondary oxygen sensor installed after the catalytic converter in the exhaust that monitors the catalytic converter's efficiency.

Besides that there are few additional emission control related vehicle systems. For example, there is an Evaporative system (EVAP), designed to prevent fuel vapors from the fuel tank from being released into the atmosphere. It also contains a number of sensors and actuators controlled by the ECU.

The ECU has self-diagnostic capability and constantly tests the operation of sensors and other components. When any of the sensor signals is missing or out of normal range, the ECU sets a fault and illuminates the "Check Engine" or "Service Engine Soon" light also called MIL (Malfunction Indication Light) storing the corresponding Diagnostic Trouble Code (DTC) in the ECU memory.

The same will happen if a mechanical component of the controlled system fails. For example, if the EGR valve fails, this will also cause the "check engine" light to come on.

The stored trouble code can be retrieved with a special diagnostic tool. The code itself does not tell exactly which part to replace, it only gives a direction where to look for. It is then up to the mechanic to use his experience to correctly identify the faulty item.

We can also reprogramme certain ECU's when replacement is neccasary. For instance Body Control Units such as Airbag control units require replacement on certain vehicles after the airbag has been deployed. The control module will need configuring to the actual vehicle itself. This is particularly the case on many French vehicles such as Peugeot, Renault and Citreon. These control modules store crash data in the ECU that can not be erased and therefore a new unit will be required once the various airbag units have been replaced. The module will then need configuring to instruct the module what Airbag configuration you have in the vehicle.

We can diagnose and repair at main dealer level on a variety of cars including:-

Alfa Romeo
Audi
Bentley
BMW
Citreon
Daewoo
Fiat
Ford
Hyundai
Isuzu
Jaguar
Kia
Lancia
Land Rover
Mazda
Mercedes
Mini
Mitsubishi
Nissan
Peugeot
Porsche
Proton
Range Rover
Renault
Rover
Saab
Seat
Skoda
Smart
Suzuki
Vauxhall
VW

This service includes coding new modules including EEC V PATS and all other modules fitted to Ford motor vehicles, EWS Syncronization on BMW cars, Key Coding on all vehicles, Engine Management ECU's fitted to all vehicles that allow programming and also AirBag and other control units as fitted to most cars.