In response to a question from another thread, I'll start a new one instead of hijacking the other. I can't remember how to make tables in this forum so what you see is what you get.

Straight from the Helm GM Electrical Diagnosis Service Manual Supplement:

COOLANT FAN TROUBLESHOOTING HINTS

Try the following checks before doing the System Check:
  1. Visually check the C. FAN fuse.
  2. If the Coolant Fan runs with the Ignition Switch off, replace the Coolant Fan Relay.
  3. If the Auxiliary Coolant Fan runs with the Igniton Switch off, replace the Auxiliary Coolant Fan Relay.
SYSTEM CHECK

Action: With the ambient temperature above 60° and the engine cold and idling, move A/C Function Selector to NORM (if equipped with A/C).
Normal Result: Coolant fan should start after a short period.

Action: Move A/C Function Selector to OFF.
Normal Result: Coolant fan turns off.

Action: With the engine warmed up, run it for at a fast idle for several minutes.
Normal Result: Coolant fan turns on before Auxiliary Coolant Fan (if equipped) and before Coolant Temperature Indicator comes on.

AUXILIARY COOLANT FAN DOES NOT TURN ON (Table 1)

Connect: FUSED JUMPER
At: COOLANT FAN TEMPERATURE SWITCH CONNECTOR (Disconnected)
Condition: Ignition Switch: RUN
Connect between: DK GRN/WHT & Ground
Correct Result: Auxiliary Coolant Fan runs.
For Diagnosis: Leave fused jumper connected and go to Table 2.

* If fan runs, replace Coolant Fan Temperature switch.

AUXILIARY COOLANT FAN DOES NOT TURN ON (Table 2)

Connect: TEST LAMP
At: AUXILIARY COOLANT FAN RELAY CONNECTOR (Disconnected)
Conditions: Ignition Switch: RUN, Fused Jumper from Table 1 still in place.

Connect Between: C (DK BLU) & Ground
Correct Result: Lamp lights.
For Diagnosis: Check C. FAN Fuse and DK BLU (351) wire for an open.

Connect Between: C (DK BLU) & B (DK GRN/WHT)
Correct Result: Lamp lights.
For Diagnosis: Check DK GRN/WHT (335) wire for an open.

Connect Between: E (RED) & Ground
Correct Result: Lamp lights.
For Diagnosis: Check Fusible Link E and RED (2) wire for an open.

* If all above results are correct, go to Table 3.

AUXILIARY COOLANT FAN DOES NOT TURN ON (Table 3)

Connect: 20 AMP FUSED JUMPER
At: AUXILIARY COOLANT FAN RELAY CONNECTOR (Disconnected)

Connect Between: E (RED) & A (BLK/RED)
Correct Result: Auxiliary Coolant Fan runs.
For Diagnosis: Leave Fused Jumper connected and go to Table 4.

* If result is correct, replace the Auxiliary Coolant Fan Relay.

AUXILIARY COOLANT FAN DOES NOT TURN ON (Table 4)

Connect: TEST LAMP
At: AUXILIARY COOLANT FAN MOTOR CONNECTOR (Disconnected)
Condition: Fused Jumper from Table 3 still in place.

Connect Between: B (BLK/RED) & Ground
Correct Result: Lamp lights.
For Diagnosis: Check BLK/RED (903) wire for an open.

Connect Between: B (BLK/RED) & A (BLK)
Correct Result: Lamp lights.
For Diagnosis: Check BLK (151) wire for an open.

* If result is correct, replace the Auxiliary Coolant Fan Motor.