Tisbury Motors Ltd


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Modern Vehicles

Tisbury Motors

01747 870258

Your local diagnostic expert
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Modern Vehicles and the need for competent technicians

Listed below are some of the computer controlled systems that you will find on the average modern car along with a basic synopsis of how they work.

Engine management

The ECU controls almost every aspect of the engine, starting with the measurement of air drawn into the engine, the correct amount of fuel to mix with that air, through to the generation of the spark at the plug and the timing of the controlled combustion generated, it then analysis the quality of the combustion by way of measuring the exhaust gases produced and not content with that it further analysis the correct operation of the catalytic convertor and therefore the emission released from the exhaust pipe.
Note at high engine RPM the spark plugs and injectors are operating at anything up to 50 times per second.

ABS brakes

The ECU continuously monitors the speed of all four wheels and cross checks one against the other, it has the capability of over riding the brake pressure applied by the drivers foot on the brake pedal, holding or releasing that pressure at individual wheels or in fact pressure generation independent of whether the foot pedal is depressed or not.

The ECU is capable of carrying out all of the above calculations and actions up to 14 times a second.

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SRS (Airbags)
The ECU monitors the rate of de-acceleration through sensors fitted about the car, once this rate has been acceded the relevant airbags can be deployed within 5thousanths of a second along with the seat belt pre-tensioners.
The latest systems have become proactive instead of reactive, what I mean by this is that the new systems weigh you when you sit in the car, there is a sensor fitted to the seat so the computer knows how far away you are from the steering wheel and there can be a miniature camera set in the “A” pillar so the ECU knows how tall you are, armed with all this information and combined with a radar sensor fitted to the front of the car (behind the grille) The ECU works out the current vehicle speed and the rate at which you are approaching the obstacle in front of you, it then knows that you are not going to stop in time, therefore it knows you are going to have the accident before you have had it. It will then take advance measures of deploying the seat belt tensioner’s and in fact the airbags in relationship to your body mass and the speed of the approaching collision this make the airbag system far better suited to the individual driver and accident.
Once you have had the accident the ECU will also automatically shut off the fuel supply, activate the hazard warning lights, turn on the interior lighting, unlock the central locking and if the vehicle is built with an internal mobile phone it will send out a signal to the emergency services.

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I have only briefly covered 3 ECU’s within the modern vehicle and to put this into prospective the average family car will currently have in excess of 30 ECU’s and a top of the range vehicle can have in excess of 200.

All of these ECU’s will communicate with each other and share information (I.E if the ABS system has a fault the Engine Management may well limit full power as a result). I hope this highlights some of the technology within the modern vehicle and therefore the importance of having fully trained technicians working on your vehicle.


Please contact Rebecca or Elaine at Tisbury Motors on 01747 870258 who will be more than happy to deal with your enquiry.

Courtesy cars are available please mention this at the time of booking so that recepton can factor this in to suit your requirements.