Engine Warm-Up Mode

This is an Open Loop mode. During engine warm-up, the PCM receives inputs from:

• Battery Voltage
• Crankshaft Position Sensor
• Engine Coolant Temperature Sensor
• Intake Manifold Air Temperature Sensor
• Manifold Absolute Pressure (MAP) Sensor
• Throttle Position Sensor (TPS)
• Camshaft Position Sensor Signal (In The Distributor)
• Park/Neutral Switch (Gear Indicator Signal-Auto. Trans. Only)
• Air Conditioning Select Signal (If Equipped)
• Air Conditioning Request Signal (If Equipped)

Based on these inputs the following occurs:

• Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off.
• The PCM adjusts engine idle speed through the idle air control (IAC) motor and adjusts ignition timing.
• The PCM operates the A/C compressor clutch through the A/C compressor clutch relay. This is done if A/C has been selected by the vehicle operator and specified pressures are met at the high and low--pressure A/C switches. Refer to Group 24, Heating and Air Conditioning for additional information.
• When engine has reached operating temperature, the PCM will begin monitoring O2S sensor input. The system will then leave the warm-up mode and go into closed loop operation.