Coolant Switch/Sensor
The 2.2L Federal engine (with automatic transmission) uses a coolant sensor, all other engines use a coolant switch. Both are located on the thermostat housing and supply signal to the computer when engine coolant temperature reaches 125°F (2.2L engine) or 150°F (1.7L engine). This information is required to prevent changing of air/fuel ratio until engine reaches operating temperature and to control amount of spark advance with a cold engine. See Fig 1.