Chart C-12C Cooling Fan Check (No Low Speed Fan)

Cooling Fan Diagnostic Chart:

A/C Head Pressure Switch Wiring Schematic:

CIRCUIT DESCRIPTION
Power for the fan motors comes from a 40A maxifuse element to terminal "30" on the relays. The relays are energized when current flows to ground through the Powertrain Control Module (PCM) Quad-Driver #4. The left fan has two speeds and the right fan is a single speed fan.
^ Low Speed (Fan 1) Relay - The PCM energizes the relay through terminal "WD11" when engine coolant temperature reaches 100°C (212°F) or when Air Conditioning (A/C) is requested.
^ High Speed (Fan 2) Relay - The high speed relay is energized by the PCM if the A/C refrigerant pressure fan switch opens, indicating refrigerant pressure above 1448 kPa (210 psi), or engine coolant temperature reaches 108°C (226°F).

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Checks for B+ at relay harness connector.
2. Jumpering terminals "87" to "30" bypasses the relay, which should cause the fans to run if fan motors and wiring are OK.
3. Selecting Fan 1 with Tech 1 scan tool "Misc. Tests" and turning fans "ON" should cause the PCM to ground CKT 335. At this point, the test light should light, if the PCM is functioning and CKT 335 isn't open.
4. This checks for B+ and ground to the fan motor. A test light "ON" at this point indicates a faulty fan motor connection or motor.