METHOD 3: FAULT CODE READERS AND SCAN TOOLS

Fault code readers vary in complexity from inexpensive devices that read out flash codes, such as the Gunson ‘Fault Finder’ shown in Fig. 3.10, to

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Fig. 3.8 The external lamp circuit for reading blinkcodes

microprocessor-based machines, such as the one described below. Gunson also market similar machines, as do many other suppliers and this is a factor that is covered in the next chapter.

The aim here is to give a reasonable description of the work involved in obtaining diagnostic information through the serial port. In effect, one connects

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Fig. 3.9 The fault code frame for the Wabco system

Fig. 3.10 A fault code reader (the Gunson ‘fault finder’)

up the tool and follows the instructions in the handbook and on the instrument’s display panel. However, in order to give an insight into the work involved I am including further details.

Figure 3.11 shows the principal parts of the diagnostic kit. There is a handheld tester, a lead to connect the tester to the vehicle’s diagnostic connector, a ‘smart card’ that matches the tester to the vehicle system under test, a printer to provide a permanent record of the test results, and leads for making connections to the battery and from the tester to the printer. This is accompanied by an instruction manual (Fig. 3.12), although it needs to be stated that once the test program has started, the display screen on the tester provides a step by step menu to guide the operator through the test sequence.

The ‘smart card’ is the equivalent of computer software and it enables the tester to use the ECM processor power to interrogate circuits. The test instrument

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Fig. 3.11 The diagnostic kit (scan tool)

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is thus able to test all circuits that are served by the ECM. The test connec- tion plug is also known as the serial port because test information is fed out serially (one bit after the other, e.g. 10110011). A considerable advantage of the serial port is that it permits testing without the need to disconnect wiring.

Unless the operator is familiar with the vehicle, it will be necessary to refer to a location chart in order to locate the diagnostic connector. Figure 3.13 shows the Rover 200 series connection point.

Fig. 3.13 The diagnostic connector

The source of power for the tester is the vehicle battery and Fig. 3.14 shows the leads being connected. The tester is placed in the position shown for the sole purpose of taking the photograph. For test purposes it is held in the hand and it should be noted that care must be taken to place the instrument in a safe position when not being held in the hand.

The next step is to connect the diagnostic lead to the vehicle’s diagnostic connector and Fig. 3.13 shows this being done. Prior to commencing the test the diagnostic lead that relates to the specific vehicle model will have been selected, as will the smart card that customizes the test instrument to the vehicle. Figure 3.15 shows the smart card being inserted.

It will be understood that different makes of vehicle require different types of diagnostic leads and smart cards. This is necessary because the diagnostic

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Fig. 3.14 Connecting to the power supply

Fig. 3.15 Inserting the ‘smart’ card to adapt the test instrument to the specific vehicle application

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Fig. 3.16 The diagnostic lead and smart card for a Ford vehicle

connections vary from vehicle to vehicle, as does the test program. Figure 3.16 shows the diagnostic lead and smart card that customizes the test instrument to a Ford vehicle. A reasonable range of diagnostic leads and smart cards is available to make this type of equipment suitable for use on a range of vehicle makes. It will be appreciated that this is an important considera- tion for the independent garage which is not linked to a particular vehicle manufacturer.

An important part of any systematic approach to fault finding, is the gathering of evidence. Figure 3.17 shows the printer being connected. It is from the printout that a permanent record of the test results will be obtained, as shown in Fig. 3.18.

When all leads have been correctly connected and steps taken to ensure that leads are clear of drive belts, hot engine parts etc., the test may commence. The manual (Fig. 3.12) gives a description of the instrument controls and, when all preparations are made, the test instrument screen displays a message which guides the operator through the test sequence.

The test procedure may require the operator to operate certain vehicle controls. Figure 3.19 shows the accelerator being depressed. Here it will be seen that a certain amount of movement around the vehicle is required during a test sequence. It is therefore important that care is exercised to ensure that leads do not become tangled, and that the vehicle is placed so that freedom of movement around it is ensured.

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Fig. 3.17 Connecting the printer

Fig. 3.18 The permanent copy of the test results

On completion of the test the printout is produced and analysis of the results can proceed. When the diagnostic and repair work is completed, the fault code is cleared, normally by following ‘on screen’ instructions. The instrument is then removed and the vehicle prepared for the road test to establish that the repair work has been effective.

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Fig. 3.19 Operating the vehicle controls during the tests