Vehicles today are fitted with many systems that are controlled by an ECU (Electronic control unit) – basically a computer. Even the most basic vehicles have an Engine Management System to control the running of the engine, Anti-lock braking, Traction control and SRS or Airbag systems. Some of the more prestige vehicles have in excess of 80 ECU’s controlling functions such as electric seats, adaptive cruise control and much more. Most of these systems communicate with each other on various networks in order to share information. Unfortunately with all of these systems faults can occur and diagnosing the cause can be extremely difficult and very costly to the customer, especially if not diagnosed correctly.
When a fault occurs in most cases a light or warning appears on the instrument panel and a fault code is logged in the computer’s memory. To diagnose the fault, a technician will connect diagnostic equipment to the vehicle diagnostic socket/port and which then can interrogate the ECU for a fault code. Sometimes the fault code description will pinpoint the component or circuit at fault, but in most cases it merely gives a hint as to what the ECU thinks the fault may be. In a lot of cases the ECU sees the symptom rather than the cause. This is where it is imperative that the Technician carries out diagnosis using a planned procedure. This is achieved by studying the data the ECU is receiving, and testing circuits and components accordingly to find the fault and it is at this point where the skill and knowledge of how to carry out these tests is absolutely vital.