SECTION 18

FAN

1.0 SUBJECT

Fan Control

2.0 SCOPE

This specification describes the logic used to implement the electronically controlled engine cooling fan.

3.0 SPECIFICATION

3.1 Fan Enable

Either of two sets of conditions can enable the low speed fan (FAN).

Condition 1:

Malf Codes 14 or 15 set or engine coolant temperature greater than or equal to *KFAN2THH*. Under this condition, the low speed fan (FAN) will be turned on after *KFANTIM1* seconds. *KFANTIM1* is the fan anticipate timer for idle air control (IAC)

Condition 2:

Malf Codes 14 or 15 not set and engine coolant temperature below *KFAN2THH* (or *KFAN2THL* if the conditions to enable the high speed have been met).

Under Condition 2, all of the following conditions must be satisfied to enable the low speed fan (FAN). The fan will be turned on *KFANTIMI* seconds after being enabled. *KFANTIM1* is the fan anticipate timer for idle air control (IAC)

1.Engine coolant temperature greater than *KFANCTHH*. The lower hysteresis value of coolant temperature is *KFANCTHL*.

2.Either conditions A, B, or C.

Condition A

• • VS A/C compressor option selected and VS fan discrete high.

Condition B

• • V5 A/C option not selected (KAFOP2, b2=0).
  • A/C discrete is selected (IACMWl b5=1).

Condition C

• • V5 A/C compressor option not selected (KAFOP2, b2=0).
  • A/C discrete low (IACMW1, b5=0).
  • A/C is active.
  • Fan run time is less than *KFANTIM2*.

3.If a MAT sensor is used in the system, manifold air temperature (MAT) A/D counts less than *KFANMTCH* (temperature exceeds a threshold). The corresponding hysteresis value of manifold air temperature is *KFANMTCL*.

4.If a MAT sensor is not used in the system, engine coolant A/D counts less than *KFANCTCH* (temperature exceeds a threshold). The corresponding hysteresis value of coolant temperature is *KFANCTCL*.

5.Vehicle speed less than *KFANVSLK* or coolant temperature greater than or equal to *KFANCLTH*. The hysteresis value of vehicle speed is *KFANVSHK*. The hysteresis value of coolant temperature is *KFACCLTL*.

3.2 Fan Disable

The following conditions will disable and turn off the low-speed fan (FAN).

Engine coolant temperature dropping below the hysteresis value *KFANCTHL*, and any of the following:

1.V5 A/C compressor option selected and V5 fan discrete low

2.V5 A/C compressor option not selected (KAFop2, b3=0), A/C is active, and FAN Run timer is greater than or equal to *KFANTIM2*.

3.v5 A/C compressor option not selected (KAFOP2, b2=0), and a/c is not active

4.If a MAT sensor is used in the system, manifold air temperature dropping below the hysteresis value *KFANMTCL*.

5.If a MAT sensor is not used in the system, engine coolant temperatures dropping below the hysteresis value *KFANCTCL*.

6.Vehicle speed dropping below the hysteresis value *KFANVSK*.