Saab 9000 Service Manual page 285

282 Fault diagnosis
Before replacing a control ·module
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 be-
fore definitely concluding that the control module is
the cause of the fault.
1 Check once again that every single point in the
diagnostic procedure for the diagnostic trouble
code in question has been carried out.
2 Study the wiring diagram of the circuit in question
and make sure you understand it. Relevant parts
of the technical description and the electrical prin-
ciples 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 1 O 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 cor-
responding wiring diagram in Service Manual 3:2
"Electrical system, wiring diagrams" as a refer-
ence.
3 In connection with removing and fitting the control
module, bear in mind its sensitivity to electrostatic
discharges. See page 283 for more detailed in-
formation.
ECM
6
G7
4 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.
5 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.
6 It has been our experience of M93-M95 that 80%
of all Trionic control modules returned in connec-
tion with repairs carried out under warranty are in
proper working order. Be restrictive with control
module replacement. Unnecessary control mod-
ule replacement represents a major cost for Saab
Automobile AB and Saab dealers. Think through
all conceivable causes of the fault before chang-
ing the control module. When another control
module is fitted as a test, always refit the original
control module.
7 If the original fault persists in spite of this, then the
control module will have to be changed.
Saab 9000