Open Loop & Closed Loop Operation
During open loop operation the PCM receives input from some engine sensors, but operates only on preset PCM programming. Oxygen sensor input is not monitored by the PCM during open loop operation. During closed loop operation the PCM monitors all sensor input (including oxygen sensor) to calculate and control fuel and ignition system operation. The fuel injection system has several operating modes. See MODES OF OPERATION under FUEL CONTROL under FUEL SYSTEMS.
Modes Of Operation
As input signals to PCM change, PCM adjusts its response to output devices. Modes of operation come in 2 types, open loop and closed loop. In open loop mode, PCM is not using input from Heated Oxygen Sensor (HO2S) and is responding to preset programming to determine injector pulse width and ignition timing. In closed loop mode, PCM adjusts ignition timing and uses input from HO2S to fine tune injector pulse width.
Following inputs may be used to determine PCM mode.
- A/C Control Positions
- A/C Switch
- Battery Voltage
- Brake Switch
- Camshaft Position Sensor
- Crankshaft Position Sensor
- Engine Coolant Temperature Sensor
- Engine Speed (RPM)
- Heated Oxygen Sensor
- Intake Air Temperature Sensor
- Manifold Absolute Pressure Sensor
- Park/Neutral Switch
- Starter Relay
- Throttle Position Sensor
- Vehicle Speed Sensor
From these inputs, PCM determines which mode vehicle is in and responds appropriately. Not all inputs are used in all modes or by all models. Modes of operation are