Doosan D20S-5 Operation & Maintenance Manual page 141

Operation Section
Advanced Diagnostics
The Fuel system has built-in diagnostics for system trouble shooting. The system has a dash mounted
malfunction indicator lamp (MIL) that provides indications of engine or fuel system related problem. Most
engine control system related problems that affect emissions or driveability of the vehicle will set a (DTC)
diagnostic trouble code and illuminate the MIL.
The MIL serves as notification to the operator of a problem related to the emission control system so the driver
can arrange for service as soon as possible. It will also display DTCs that have been stored due to a system
malfunction.
The MIL should illuminate when the key is in the ON position and the engine is not running. This feature
verifies that the lamp is in proper working order. If the MIL does not illuminate with the vehicle key
ON/engine OFF, repair it as soon as possible. Once the engine is in start or run mode, the MIL should turn
off. If the lamp remains on while the engine is in the start or run mode a diagnostic trouble code may be set.
The MIL will be turned OFF after three (3) consecutive run cycles or by clearing the active code with the
Diagnostic Scan Tool (DST).
Diagnostic Trouble Codes are set when the GCP (Electronic Control Module) runs a diagnostic self test and
the test fails. When a DTC is set, the ECM will illuminate the MIL on the instrument panel and also save the
DTC in memory. The ECM will continue to run the self test. If the system continues to fail the test, the lamp
will stay illuminated and the DTC is stored as an active DTC. If the self test runs and passes, the DTC will be
stored as historic DTC. All DTCs are stored as historic faults until they are cleared. Most DTCs will
automatically clear from memory if the DTC does not reset within 50 to 100 consecutive engine run cycles.
While a Diagnostic Trouble Code is current for a sensor, the ECM may assign a default "limp home" value and
use that value in its control algorithms. All of the system diagnostic self-tests run continuously during normal
vehicle operation.
The Diagnostic Trouble Codes can be read by using either the MIL lamp or a laptop computer. Diagnostic
Trouble Codes can be cleared from memory with a laptop computer, or by turning the ignition key to the OFF
position and removing the ECM power fuse or battery cable for at least 15 seconds.
If more than one DTC is detected, start the diagnostic repair with the lowest DTC number set. Diagnose
each problem to correction unless directed to do otherwise by the diagnostic chart. The DTCs are numbered
in order of importance. Both DTC 112 and DTC122 pertain to the oxygen sensor, so it is possible that a
repair that corrects DTC 112 may also correct the problem causing the DTC 122.
Diagnostic test charts contained in this manual refer to the DST to be connected and in the "System Data
Mode." This simply means that the DST is connected and communicating with the PC. In some instances
the chart will call out a special test mode. An example of this would be instructions for the DST to be
connected and in the DBW (drive by wire) mode. Always be sure to follow the special instructions to avoid a
false diagnosis of fuel system components.
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