Repair instructions Group 30: Electrical system
14
Repair instructions
General advice
The following advice must be followed to avoid dam-
age to the MDl unit and other electronics.
IMPORTANT! The system must be disconnect-
ed from system voltage (by cutting the current
with the main switch) when the MDI connectors
are disconnected or connected.
Never disconnect the current with the main switch-
es when an engine is running.
Never undo a battery cable when the engine is
running.
Turn the main switches off or disconnect the bat-
tery cables during quick charging of the batteries.
NOTE! During normal floating charging, it is not
necessary to turn the main switches off.
Only batteries may be used for start help. A help
start device can produce a very high voltage and
damage the control unit and other electronics.
If a connector is disconnected from a sensor, be
very careful to avoid allowing the contact pins to
come into contact with oil, water or dirt.
Fault tracing of cables and
connectors
Special tools: 9812519
Check all connectors visually
Check the following:
● Look for oxidation which can impair contact in con-
nectors.
● Check that terminals are undamaged, that they
are correctly inserted into their connectors, and
that the cable is correctly terminated in the termi-
nal.
● If possible, shake the cables and pull the connec-
tors during measurement to discover whether the
cable harness is damaged.
● Check that the cables are not damaged. Avoid
clamping cables in tight bends close to the con-
nector.
Contact problems
Intermittent contact or temporary recurring faults can
be difficult to fault trace, and are frequently caused by
oxidation, vibration or poorly terminated cables.
Wear can also cause faults. For this reason, avoid
disconnecting a connector unless it is necessary.
Other contact problems can be caused by damage to
pins, sockets and connectors etc.
Shake cables and pull connectors during measure-
ment, to find where the cable is damaged.
Contact resistance and oxidation
Resistance in connectors, cables and junctions
should be 0 Ω. A certain amount of resistance will oc-
cur, however, because of oxidation in connectors.
If this resistance is too great, malfunctions occur. The
amount of resistance that can be tolerated before
malfunctions occur varies, depending on the load in
the circuit.
Open circuit
Possible reasons for faults could be chafed or broken
cables, or connectors which have come undone.
Use the wiring diagram to check the cables which are
relevant to the function. Start off with the most proba-
ble cable in the circuit.
Check the following:
● Disconnect the relevant connector at each end of
the cable harness.
● Use multimeter 9812519 to measure the resis-
tance between the ends of the cable.
Nominal value ~ 0 Ω.
● If possible, shake the cables and pull the connec-
tors during measurement to discover whether the
cable harness is damaged.
● Check the next cable system in the wiring sched-
ule if no fault has been found.
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