|
Introduction to code reading |
|
|
|
Page 2 of 3 Sensors are prone to failure mainly due to being exposed to the harsh engine environment where harness connections can easily deteriorate over a few years. If this kind of fault occurs the ECM can be misled by the information being sent from the sensor, this results in the wrong quantity of fuel or timing for the sparks. Soon the car allows too much of the wrong exhaust gasses to escape, becomes difficult to drive, or even does not start at all.The ECM is able to detect faults in sensor signals by comparing the value with a range of values that are programmed by the designer of the ECM. If a signal is outside the expected range then something is wrong! The ECM does not "know" what exactly is wrong but it can sense that the signal is not in the range it expects to receive. This detected fault is stored as a code number in the memory of the ECM and it is this code that is known as a "fault-code". ECM designers have built-in a limited number of such fault-codes into most modern systems. Each manufacturer has a different coding system and a different way of reading the codes, but they have some basic similarities. Somewhere on the car's harness (usually under the bonnet) is a Diagnostic Socket that connects directly to the ECM, by connecting a second computer to this socket we can send messages back and forth between the two computers and read the stored codes. A simple code reader will show only the two or three digit code numbers which you then need to look up in a book to find out what they mean. A more sophisticated code reader does much more, by READING, CLEARING, ACTUATOR TESTS, and COMPONENT TESTS. We are able to READ CODES and display the meaning of each code for example if the coolant temperature sensor is faulty then on some Bosch ECMs the fault-code stored is "15".
|
Articles