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Engine Control System & Engine Component Tests - 3.8L: Overview Pontiac Firebird IV

Testing & Diagnostics ~364 words

MODEL IDENTIFICATION

ApplicationSpecification
Camaro/FirebirdVIN K

VIN IDENTIFICATION

Description

When A/C is selected, a 12-volt signal is supplied to the A/C request input of PCM. A/C compressor clutch relay is controlled through PCM. PCM monitors A/C refrigerant pressure. If A/C refrigerant pressure and engine operating conditions are within a specific calibrated acceptable range, PCM will enable A/C compressor relay. This is done by providing a ground path for A/C relay coil within PCM. When A/C compressor relay is enabled, battery voltage is supplied to A/C compressor clutch coil.

PCM will enable A/C compressor clutch whenever engine is running and A/C has been requested, unless

  1. Throttle angle is greater than 90 percent.
  2. A/C head pressure is greater than 414 psi (29.1 kg/cm 2 ).
  3. A/C head pressure is less than 35 psi (2.5 kg/cm 2 ).
  4. Ignition voltage is less than 10.5 volts.
  5. Engine speed is greater than 4500 RPM for 5 seconds.
  6. Engine coolant temperature is greater than 257°F (125°C).
  7. Intake air temperature is less than 41°F (5°C).

Power for cooling fan motors comes from a fusible link at battery junction block. Relays are energized when current flows from A/P FAN fuse (25-amp) through relay coils to ground through Powertrain Control Module (PCM). No. 1 cooling fan relay control circuit is grounded for low speed fan operation. Relay control circuits for all 3 cooling fan relays are grounded for high speed fan operation.

During low speed fan operation, PCM supplies a ground path for No. 1 cooling fan relay. This closes relay contacts, allowing current to flow from battery junction block through relay and to cooling fan motor No. 1 (left side). Ground path for cooling fan motor No. 1 is through No. 3 cooling fan relay and cooling fan motor No. 2 (right side). The result is a series circuit with both fans running at low speed.

During high speed fan operation, PCM supplies a ground path for all 3 cooling fan relays. This closes all 3 fan relays. At high speed, both cooling fan motors are supplied current from battery junction block and each fan motor has its own ground.

See also:
• ADJUSTMENTS - 3.8L

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