For 1990-2009 cars

### Coolant Fan Circuit Operation

The engine cooling system consists of the following components:

• | One engine coolant fan

• | Two auxiliary coolant fans (#1 and #2)

• | Two temperature switches (primary cooling fan temperature switch and secondary cooling fan temperature switch)

• | One A/C compressor refrigerant pressure switch

• | One ECM cooling blower

• | One timing control pump

• | One auxiliary water pump

• | Seven fan control relays

• | One engine coolant fan resistor

These components operate as follows:

B+ is supplied to the auxiliary water pump whenever the ignition switch is in the ON position. At 100°C (212°F), the primary cooling fan temperature switch stage 1 will close, enabling the ECM relay K48 and the fan control relay K26 to energize. When the ECM relay K48 energizes, B+ is applied to the ECM cooling blower allowing it to operate. When the fan control relay K26 energizes, B+ from fuse #52 is applied to the auxiliary coolant fan #1 and to the auxiliary fan #2 through the normally open contacts of the fan control relay K52. This will cause the auxiliary coolant fans (#1 and #2) to operate in series at half speed. The fan control relay K26 will also supply B+ to the engine coolant fan after it goes through the engine coolant fan resistor. The engine coolant fan resistor will cause the engine coolant fan to operate at half speed. The fan control relay K26 will supply B+ to the timing control pump through the normally closed contacts of the auxiliary water pump relay K22. This will allow the timing control pump to operate. The primary cooling fan temperature switch stage 1 contacts will open when the coolant temperature reaches 95°C (203°F). This will turn all three fans, the ECM cooling blower, and the timing control pump OFF, unless the air conditioning system is ON.

If the ignition switch is in the OFF position and the coolant temperature is above 100°C (212°F), both of the auxiliary engine coolant fans (#1 and #2), the engine coolant fan, and the timing control pump will remain ON until the coolant temperature drops below 95°C (203°F).

If the temperature reaches 105°C (221°F), the secondary cooling fan temperature switch contacts will close enabling the fan control relays K52 and K28 to energize. When the fan control relay K52 energizes, the auxiliary engine coolant fan #1 will go to full speed because it is no longer in series with the auxiliary engine coolant fan #2. When the fan control relay K28 is energized, B+ from fuse #40 will allow the auxiliary engine coolant fan #2 to go to full speed. With the stage 1 contacts of the primary cooling fan temperature switch closed, the ECM cooling blower, the timing control pump, and the engine coolant fan will continue to operate. The secondary cooling fan temperature switch contacts will open when the coolant temperature reaches 100°C (212°F). This will cause the operation of the auxiliary engine coolant fans (#1 and #2) to operate differently as the primary cooling fan temperature switch designates.

If the coolant temperature reaches 110° (230°F), the secondary cooling fan temperature switch stage 2 will close enabling the fan control relay K67 to energize. When the fan control relay K67 energizes, B+ from fuse #42 will be applied to the engine coolant fan directly. This will cause the engine coolant fan to operate at full speed. All the other operations that were taking place before the coolant temperature reached 110°C (230°F) will remain in effect. The primary cooling fan temperature switch stage 2 contacts will open when the coolant temperature reaches 105°C (221°F) and the engine coolant fan will return to half speed.

At coolant temperatures above approximately 110°C (230°F), all three coolant fans are operating at full speed. The ECM cooling blower, the timing control pump, and the auxiliary water pump are also operating. Only six of the seven relays operate at this time, unless the air conditioning system is turned ON. In this case, the fan control relay K87 and the A/C compressor relay K60 will also operate.

In order to prevent inadmissible high refrigerant pressure in the refrigerant circuit, the auxiliary engine coolant fans (#1 and #2) are switched from the first speed to the second speed at refrigerant pressures above approximately 1,900 kPa (275 PSI). When the pressure drops below approximately 1,500 kPa (217 PSI), the auxiliary engine coolant fans (#1 and #2) are switched back to the first speed.