Chart C-12B Coolant Fan Control Circuit

Cooling Fan Control Circuit Diagram:

CIRCUIT DESCRIPTION:

Power for the fan motors comes from a 40 amp maxi fuse element to terminal "1" on the relays. The relays are energized when current flows to ground through the PCM quad drivers. The left fan has two speeds and the right fan has a single speed.

Low Speed Fan Operation
The PCM energizes the fan relay through terminal "GC4" when the coolant temperature reaches 101°C (214°F) or A/C requested.

High Speed Fan Operation
High Speed Fan Operation
High Speed Fan Operation
The high speed relay is energized by the PCM if the A/C refrigerant pressure reaches 1448 kPa (210 psi), or when coolant temperature exceeds 108°C (226°F)

TEST DESCRIPTION:
Numbers below refer to circled numbers on diagnostic chart.

Chart C-12B, Fan "ON" Always:

1. Checks to see is CKT 1269 is shorted to ground, which would keep the relay closed at all times.
2. Checks to see if CKT 1270 is shorted to ground. A light indicates the wire is shorted to ground. The following steps will isolate the short.
3. If the test light is "OFF" after disconnecting the PCM, be sure CKT 1269 is not shorted to B+. If not shorted to B+, the PCM is shorted internally.
4. If the test light is "OFF" after disconnecting the PCM, be sure CKT 1270 is not shorted to B+. If not shorted to B+, the PCM is shorted internally.


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