Advanced automotive fault diagnosis Figure 3.15

which are coming into use more and more fre-
quently in new vehicles. The testers are con-
nected directly to the diagnostics socket via a
serial diagnostics interface by means of an adapter
cable.
The system automatically detects the control
unit and reads out the actual values, the error
memory and other controller-specific data. Thanks
to a built-in multiplexer, it is even easier for the
user to diagnose the various systems in the vehicle.
The multiplexer determines the connection in 
the diagnostics socket so that communication is
established correctly with the selected control
unit.
The sequence of images shown below detail a
number of steps taken to diagnose a fault, using
the KTS, on a vehicle that had poor running
symptoms and the MIL was illuminated.
(My thanks to Kevin and Steve at the Bosch
training centre for their help with this section.)
Tools and equipment
37
The first step in this procedure was to connect
the equipment to the car’s diagnostic socket. The
ignition should be off when the connection is
made and then switched on.
On this system the data for a wide range of
vehicles is included on the system. The particu-
lar make and engine, etc. can be selected from
the menu system.
The standard test for stored diagnostic trouble
codes (DTCs) was run and the result suggested
that there was a fault with the air flow sensor.
The specific fault was that the signal value was
too low. No real surprise as we had disconnected
the sensor to simulate a fault!
Connect the serial lead to the diagnostic socket
Choose the vehicle type
Take a readout from the control unit memory (DTC display)

38
Advanced automotive fault diagnosis
This is the connection that was causing the prob-
lems. Further information about its pin configura-
tion can be looked up in the Esitronic database.
The system also provides typical readings that
should be obtained on different pins. For exam-
ple, the supply and earth as well as the signal 
outputs.
Additional tests can be carried out to deter-
mine the fault.
The faulty connection was repaired and general
checks carried out to ensure no other compo-
nents had been disturbed during the testing and
repair process.
Air flow sensor connection
Esitronic information for the air flow sensor
Make repairs
The final task is to clear the fault code memory
and turn off the malfunction indicator light
(MIL).
Road tests showed that the fault had been
rectified.
Erase the fault from the memory

Tools and equipment
39
Knowledge check questions
To use these questions, you should first try to answer them without help but if necessary, refer back to
the content of the chapter. Use notes, lists and sketches to answer them. It is not necessary to write
pages and pages of text!
1. Explain why a good multimeter has a high internal resistance.
2. List three advantages of using an oscilloscope for testing signals.
3. Describe how a scanner is connected to a vehicle and what information it can provide.
4. State what is meant by the term ‘accuracy’.
5. List five tests carried out on a vehicle using a pressure gauge.

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