4.6L DEVILLE & SEVILLE: Description

Engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. Relays are arranged in a series/parallel configuration that allows Powertrain Control Module (PCM) to operate both fans together at low or high speeds. Cooling fans and fan relays receive battery voltage from underhood fuse block.

During low speed operation, PCM supplies ground path for low speed fan relay through low speed cooling fan relay control circuit. This energizes cooling fan 1 relay coil, closes relay contacts, and supplies battery voltage through cooling fan motor supply voltage circuit to right cooling fan. Ground path for right cooling fan is through cooling fan series/parallel relay and left cooling fan. Result is a series circuit with both fans running at low speed.

During high speed operation, PCM supplies ground path for cooling fan 1 relay through low speed cooling fan relay control circuit. After a 3-second delay, PCM supplies a ground path for cooling fan 2 relay and cooling fan series/parallel relay through high speed cooling fan relay control circuit. This energizes cooling fan series/parallel relay coil, closes relay contacts, and provides a ground path for right cooling fan. At the same time, cooling fan 2 relay coil is energized closing relay contacts and provides battery voltage on cooling fan motor supply voltage circuit to left cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. Result is a parallel circuit with both fans running at high speed.

PCM commands low speed fans on under the following conditions:

• Engine coolant temperature exceeds approximately 223°F (106°C).
• Transmission fluid temperature exceeds 302°F (150°C).
• A/C operation is requested.
• After vehicle is shut off, if engine coolant temperature at key-off is greater than 304°F (151°C) and system voltage is more than 12 volts. Fans will stay on for approximately 3 minutes.

Engine cooling fans will switch from low to off when coolant temperature drops less than 216°F (102°C).

PCM commands high speed fans on under the following conditions:

• Engine coolant temperature reaches 234°F (112°C).
• Transmission fluid temperature is more than 304°F (151°C).
• When certain DTCs set.

Engine cooling fans will switch from high to low, except when DTCs set, when coolant temperature drops less than 223°F (106°C).