Before replacing a control module
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Before replacing a control module
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When all tests and checks have been carried out in accordance with the
diagnostics procedure for the relevant diagnostic trouble code, or by manual fault diagnosis,
without any faults having been found, it is natural to assume that the control module is at fault.
Check through the following points very carefully before definitely concluding that the
control module is the cause of the fault.
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1.
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Check once again that every
single point in the diagnostic procedure for the diagnostic trouble code in question has been
carried out.
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2.
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Study the wiring diagram of the circuit in question and make sure you understand
it. Relevant parts of the technical description and the electrical principles of operation
described in Service Manual 3:2 "Electrical System, wiring diagrams" may be of assistance in
this respect. The wiring diagram in this manual was finalized about 10 weeks before the start
of production. In the event of any discrepancies between it and the wiring of the car you are
working on, use the corresponding wiring diagram in Service Manual 3:2 "Electrical system,
wiring diagrams" as a reference.
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3.
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In connection with removing and fitting the control module, bear in mind its
sensitivity to electrostatic discharges. See
for more detailed
information.
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4.
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Check all grounding points and the power supply for the control module. If you
have already done so, do it once again. Make sure that power ground and sensors are
mechanically and electrically separate.
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5.
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If the suggested fault diagnosis procedure does not produce satisfactory results,
try to trace the fault by measuring and analyzing components and circuits on the basis of "Test
readings, control module connections". Connect a BOB or SIM.
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6.
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It has been our experience of M93-M95 that 80%% of all Trionic control modules
returned in connection with repairs carried out under warranty are in proper working order. Be
restrictive with control module replacement. Unnecessary control module replacement
represents a major cost for Saab Automobile AB and Saab dealers. Think through all
conceivable causes of the fault before changing the control module. When another control
module is fitted as a test, always refit the original control module.
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7.
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If the original fault persists in spite of this, then the control module will have to be
changed.
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