C-12, Cooling Fan Circuit Diagnosis: Description

Power for fan motors comes from a fusible link at battery junction block. Relays are energized when current flows from FANS/ACTUATOR fuse through relay coils to ground through PCM. PCM Output Driver Module (ODM) "B" output No. 1 is for low speed fan operation. PCM ODM "B" outputs No. 1 and 2 are for high speed operation.

During low speed fan operation, PCM supplies a ground path for the low speed fan (fan No. 1) relay through ODM "B" output No. 1. This closes low speed relay contacts and current flows from battery junction block through relay and to primary cooling fan. Only ground path for primary fan is through series/parallel relay, and fan No. 1 motor. The result is a series circuit with both fans running at low speed.

During high speed fan operation PCM supplies a ground path for low speed (fan No. 1) fan relay through ODM "B" output No. 1. PCM also supplies a ground path for high speed (fan No. 2) relay and series/parallel relay through ODM "B" output No. 2. This closes all 3 fan relays. At high speed, primary and secondary cooling fans are both supplied current from battery junction block and each fan has its own ground.