Fault Code 2 6


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

Fig. 3.12 The instruction manual

is thus able to test all circuits that are served by the ECM. The test connection 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

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

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

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 consideration 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.

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.

Fig. 3.19 Operating the vehicle controls during the tests

3.2 Developments in self-diagnosis

The above descriptions give a reasonable overview of the methods of 'reading' diagnostic trouble codes. I now propose to look at more recent developments that have arisen from legislation and advances in technology.

From the foregoing review of methods for accessing fault codes it will be evident that there are many different methods in use. In many cases, vehicle manufacturers have developed a version of diagnostic equipment that is unique to their range of vehicles. When an equipment manufacturer makes a piece of diagnostic equipment which has capabilities to perform diagnostic work on a range of vehicles, it is normally accompanied by an extensive range of leads and adapters so that it can be configured to suit a particular vehicle.

For several years now there have been arguments for and against bringing a degree of standardization into automotive computer applications, particularly in the area of access to diagnostic information. Generally speaking, there are two driving forces that cause changes to occur; one is legislation and the other is changes in technology. In the automotive field, as in other areas where computers are used, the technology has changed rapidly.

In the area of legislation, the world-wide concern with the effects of atmospheric pollution has had a major effect on vehicle design and, quite naturally, enforcement authorities are anxious to ensure that vehicles comply with the current emissions regulation. The result is that there have been major developments that cause vehicles in the USA to be equipped with a standard means of access to emissions related data and it is anticipated that Europe will follow a similar path in the near future. As the USA has a major influence on events in technology, it is to be expected that their developments will have an effect on vehicle technology in Europe and elsewhere. There is plenty of evidence to show that this is the case and readers should benefit from a review of some recent developments, such as on board diagnostics (OBD).

The term on board diagnostics refers to the self-diagnosing capabilities that are carried in the computers on the vehicle, and the aids that are provided to make the diagnostic data available to authorized users. Off-board diagnostics is equipment such as scan tools, oscilloscopes and other test equipment. In most cases both types of equipment are required for vehicle repair work. To date (January 2000) there have been two versions of OBD, i.e., OBD I and OBD II. Both apply to the USA, but introduction of similar legislation for Europe is imminent.

This required vehicles produced from 1988 onwards to be equipped with electronically (computer) controlled systems that were capable of monitoring themselves. Any malfunction (defect) that affected exhaust emissions must be displayed on a warning lamp, known as the malfunction indicator lamp (MIL), on the dashboard. The malfunction must be stored in the ECM's memory and it must be readable with the aid of 'on board' facilities, e.g. a flash code on a lamp.

OBD II strengthens the requirements of OBD I on vehicles of model year 1994 and afterwards. OBD II applies to spark-ignition cars and light vans, and from 1996 onwards to diesel-engined vehicles. The main features are that the following emissions related systems must be continuously monitored:

• combustion

• catalytic convertor

• oxygen (lambda) sensors

• secondary air system

• fuel evaporative control system

• exhaust gas recirculation system.

The requirements for diesel-engined vehicles vary and glow plug equipment may be monitored instead of the catalytic converter. Features of OBD II are as follows.

• The malfunction indicator lamp (MIL) is provided with an additional 'flashing' function.

The DTCs can be read out by a standard form of scan tool, via a standardized interface that uses a 16-pin diagnostic connector of the type shown in Fig. 3.20.

• The emissions-related components must be monitored for adherence to emissions limits in addition to monitoring them for defects.

• Operating conditions (performance data) can be logged and stored in a 'freeze frame'.

CARB plug:

Pin 7 and 15: Data transfer in accordance with DIN ISO 9141-2

Pin 2 and 10: Data transfer in accordance with SAE J 1962

Pin 1, 3, 6, 8, 9, 11-14 are not assigned to CARB. (OBD II data administration guideline "OBDII-DV") Pin 4: Vehicle ground (body) Pin 5: Signal ground Pin 16: Battery positive

Fig. 3.20 The SAE J 1962 standardized diagnostic link connector (DLC)

The fault codes consist of five digits.

Digit 1 identifies the vehicle system.

Digit 2 identifies the sub-group

Digit 3 identifies the subassembly

Digits 4 and 5 identify the localised system components.




Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

Don't pay hundreds of dollars to find out what is wrong with your car. This book is dedicated to helping the do it yourself home and independent technician understand and use OBD-II technology to diagnose and repair their own vehicles.

Get My Free Ebook

Post a comment