D439E Service Manual 4. Fuel system
167
Engine Control System-
Electronic
Description
Inspection of The Diesel Control System
If the components of the diesel control system
(sensor ECM, Injector etc) has a problem, the
proper amount of fuel for various engine-operating
conditions is not supplied so that the following
situations can occur.
1. Engine is hard to start or does not start at all.
2. Idling is unstable
3. Engine drive performance is bad.
If any of the above conditions are met first perform a
routine diagnosis that includes basic engine checks
(ignition system malfunction, incorrect engine
adjustment etc). Then, inspect the components of
the diesel control system with multi-purpose tester
or digital multi-meter.
CAUTION
• Before removing or installing any part, read the
diagnostic trouble codes and then, disconnect
the battery negative (-) terminal.
• Before disconnecting the cable from battery
terminal, turn the ignition switch to OFF. If the
battery cable is removed or connected during
engine operation or the situation in which the
ignition switch is ON, then the ECU
semiconductor could be damaged resulting in
inaccurate operation.
Self-Diagnosis
The ECU sends the input/output Signals (some
Signals at all times and the others under specified
conditions). When some time elapse after the first
detection of unusual signal, the ECU judges an
irregularity and it records the diagnostic trouble code.
And then it outputs the signal to the self-diagnosis
output terminal. The diagnosis results can be
checked by the Hi-scan. In addition, Diagnostic
Trouble Codes (DTC) will be directly backed up by
the battery so that it will remain in the ECU even if
the ignition switch is turned off. The diagnostic
trouble codes will, however, be erased when battery
terminal or ECU connector is disconnected.
CAUTION
If a sensor connector is disconnected with being
the ignition switch turned ON, the diagnostic
trouble code (DTC) is recorded in most diesel
control unit. In this case, if the battery negative
terminal (-) is disconnected for 15 seconds or
more, then the diagnosis memory will be erased.
Self-Diagnosis Checking Procedure
• Since diagnosis memory is erased if the battery or
the ECU connector is disconnected, don’t
disconnect the battery just until the diagnostic
trouble codes are completely read and recorded
safely.
• It is most desirable to erase the diagnostic trouble
codes using Hi-scan after completing check and
repair. After disconnecting ground cable from the
battery negative (-) terminal for 15 seconds or more,
reconnect the cable and check if the trouble codes
have been erased. (At this time, ignition switch
must be turned off).
Inspection Procedure (With Hi-scan)
1. Turn off the Ignition switch
2. Connect the Hi-scan connector to the connector
of DLC (Data Link Connector) of the trouble
diagnosis as shown in the following figure.
3. Turn the ignition switch ON.
4. Check the diagnostic code using Hi-scan
5. Repair the parts having faulty shown in the
diagnosis chart.
6. Erase the diagnostic trouble codes.
7. Disconnect the Hi-scan.
CAUTION
• When the battery voltage is excessively low,
diagnostic trouble codes cannot be read. Be
sure to check the battery for voltage and the
charging system before starting the test.
• When using a tester manufactured by other
company, operate the tester by referring to the
manual of the company.
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