Autodata - Diagnostic Trouble Codes Fault locations and probable causes - 2004 edition

Trouble codes
All the systems covered by this manual are controlled by a module which incorporates a self-diagnosis function. These control
modules are capable of detecting certain faulty signals and storing them for access later.
In many cases the detection of a faulty signal will cause the control module to invoke the limp-home mode, which adopts a
mean signal value (programmed into the control module memory), to enable the vehicle to be driven until the fault can be
diagnosed and rectified.
In many early models faults are signalled by numerical trouble codes comprising two, three or four digits, which can be
interpreted by reference to the code tables in this manual. Later models have EOBD codes which are mandatory on new
vehicles produced after January 2000.
Trouble codes on early models may be displayed by an LED on the control module, or on the fascia mounted malfunction
indicator lamp (MIL). If this is not possible then an LED tester can sometimes be used at the data link connector (DLC).
If access to trouble codes is possible in this manner it is described along with the relevant code table.
Many later models and those that comply with EOBD regulations may require a scan tool to enable the trouble code
information to be displayed.
Self-diagnosis for fuel injection, mapped ignition and integrated engine management systems has been used for many years,
but with the more recently introduced electronically controlled transmissions and immobilizer systems, the scope for trouble
code based fault diagnosis has expanded considerably and the adoption of European On-Board Diagnostics (EOBD) has
brought a degree of standardisation.
Engine management
The engine control module (ECM) processes the load and temperature signals received from the system sensors and
controls the fuellair ratio, idle speed, ignition timing and other functions through outputs to the actuators, such as injectors,
idle speed control (1%) valve, evaporative emission (EVAP) canister purge valve etc.
As emission regulations have become more stringent, more systems, such as throttle control, cruise control,
transmissions and immobilizers have been linked to the ECM.
The ECM self-diagnosis fault memory will log trouble codes if certain inputs or outputs are outside the programmed
parameters and may invoke 'limp home' substitute values for any out-of range signals, to enable the vehicle to continue to
be driven until repairs can be carried out.
Fig. 1
-
Air
n
-TIl
Engine control module
M+
Mter
air flow
Throttle
position t-
switch or sensor
Intake-air
temperature
sensor I
.
I I I I \
Throttlevalve
I
Idle speed
control
valve
[Autodata L Trouble
I
Engine intake manifold
Typical engine management system
I
AD84398
codes 53
4