Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSSUBARU1991XT 4WD F4-1781CC 1.8L SOHCREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTIGNITION SYSTEMRELAYS AND MODULES - IGNITION SYSTEMIGNITION CONTROL MODULETESTING AND INSPECTION
1991 Subaru XT 4WD F4-1781cc 1.8L SOHC
Ignition Control Module: Testing and Inspection
1991 Subaru XT 4WD F4-1781cc 1.8L SOHCSECTION Testing and Inspection
Ignition Control System Schematic:
A faulty ignition system power transistor does not set a trouble code in the on-board diagnostic system. Refer to the schematic diagram and test the system with the diagnostic chart.
Wire color code identification:
L: Blue
B: Black
Y: Yellow
G: Green
R: Red
W: White
Br: Brown
Lg: Light green
Gr: Gray
Ignition Control System Diagnostic Chart (a):
Ignition Control System Diagnostic Chart (b):
Ignition Control System Diagnostic Chart (c):
IGNITION CONTROL SYSTEM DIAGNOSTIC CHARTS
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.