Chart C-12A Functional Check

Cooling Fan Circuit:

Circuit Description:
Power for the fan motor comes from a 40A maxi fuse element to terminal "A" on the relays. The relays are energized when current flows to ground through the PCM (Quad Driver).

Puller Relay - The PCM energizes the relay through terminal "GC4" when the coolant temperature reaches 100°C (212°F) or when A/C is requested.

Pusher Relay - The pusher relay is energized by the PCM if the A/C refrigerant pressure reaches 210 psi (1448 kPa) or the coolant temperature reaches 108°C (226°F).

Chart C-12A Diagnostic Chart:

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Using the Tech 1 misc. tests, low speed fan control will cause the PCM to ground CKT 335 and the puller fan should run.

2. Selecting high speed fan with the Tech 1 allows control of CKT 473 and the pusher fan relay.

3. When jumping the coolant temperature sensor wires together "Scan" should display coolant temperature of 151°C (304°F). Both fans will be "ON" when the key is cycled from "OFF" to "ON."

4. Opening the A/C pressure switch harness will cause the pusher fan to run.


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 Harness - Inspect PCM harness connectors for backed out terminals "GC4" or "GC3", 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 Coolant Temperature Sensor (CTS) See "Coolant Sensor Temperature vs. Resistance Values" table DTC 15

Basic Cooling System Problem - Refer to engine cooling and radiator diagnosis.