Mitsubishi 1989-1993 GALANT Service Manual page 615

INTAKE AND EXHAUST
SERVICE POINTS OF REMOVAL
4. REMOVAL OF OXYGEN SENSOR
Disconnect the connector of the oxygen sensor, and install
the special tool to the oxygen sensor.
Then, using an offset (box-end) wrench, remove the
oxygen sensor.
INSPECTION
Check the following points; replace the part if a problem is
found.
EXHAUST MANIFOLD
Check for damage or cracking of any part.
EXHAUST MANIFOLD GASKET
Check for flaking or damage of the gasket.