Chart C-12A Coolant Fan Functional Check

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 (2l2°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 l08°C (226°F).

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Using the Tech 1 scan tool "Misc. Tests," Fan 1 control will cause the PCM to ground CKT 335 and the cooling fans should run at low speed.
2. Selecting Fan 2 with the scan tool allows control of CKT 473 and the high speed (Fan 2) relay.
3. Disconnecting the A/C refrigerant pressure fan switch harness connector will cause the PCM to energize the high speed (Fan 2) relay.

DIAGNOSTIC AIDS
An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation.
Check for:
^ Poor connection or damaged hamess - Inspect PCM harness connectors for backed out terminals "WD10" or "WD11", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.
^ Intermittent test - If connections and harness check OK, a digital voltmeter connected from affected terminal to ground while moving related connectors and wiring harness. If the failure is induced, the voltage reading will change.
^ Mis-scaled Engine Coolant Temperature (ECT) sensor - Refer to ECT Temperature vs Resistance Values in System Diagnosis/Diagnostic Charts/Diagnostic Trouble Code Charts/Diagnostic Trouble Code (DTC) PO118. P0118

^ Basic cooling system problem - Check engine cooling and radiator systems.