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 Oxygen (O2) sensors 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 O2 sensors to fine tune injector pulse width. 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 as follows.

1. Ignition Switch (Key-On) Mode
   
   This is an open loop mode. PCM pre-positions IAC motor based on engine coolant temperature. PCM determines atmospheric pressure from MAP sensor and determines basic fuel strategy. PCM modifies fuel strategy according to intake air temperature, coolant temperature and throttle position sensor inputs. PCM activates auto shutdown relay, which in turn activates fuel pump for only 3 seconds unless engine is cranked. Fuel pump relay also energizes O2 sensor heater element for approximately 2 seconds unless engine is cranked, but PCM does not use O2 sensor input to calibrate air/fuel ratio during this mode.
2. Engine Start-Up Mode
   
   This is an open loop mode. When starter is engaged, PCM receives input from battery voltage, starter relay, CKP sensor, CMP sensor, ECT sensor, IAT sensor, MAP sensor and TP sensor. Based on these inputs, voltage is applied to fuel injectors with PCM controlling injection sequence, rate, and pulse width. PCM provides ground for injectors to fire in proper order. PCM determines proper ignition timing according to input received from CKP sensor. If PCM does not receive CKP sensor signal within 3 seconds after engine begins cranking, fuel injection system is shutdown and a Diagnostic Trouble Code (DTC) is set in PCM memory.
3. Engine Warm-Up Mode
   
   This is an open loop mode. PCM determines injector pulse width using input information from battery voltage, CMP sensor, CKP sensor, ECT sensor, IAT sensor, MAP sensor and TP sensor. PCM also monitors A/C request and P/N switch (A/T only) for fuel calculation. PCM controls engine idle speed through IAC motor. PCM controls ignition timing based on CKP sensor input. PCM also operates A/C compressor clutch (if A/C is requested) through A/C clutch relay. When engine reaches operating temperature, PCM will begin monitoring O2 sensor input and go into closed loop operation.
4. Idle Mode
   
   This is a closed loop mode when engine is at operating temperature. In idle mode, PCM now adds O2 sensor signal to array of inputs used in Engine Warm-Up Mode. PCM maintains correct air/fuel ratio by adjusting injector pulse width and ignition timing. PCM also controls A/C clutch operation (if A/C is requested).
5. Cruise Mode
   
   When engine is at operating temperature, this is a closed loop mode. Using information from A/C switch, battery voltage, CMP sensor, CKP sensor, ECT sensor, IAT sensor and MAP sensor. PCM also monitors A/C request and P/N switch (A/T only) and TP sensor signals for fuel calculation. PCM monitors O2 sensor and adjusts air/fuel ratio as needed. PCM controls engine idle speed through IAC motor. PCM adjusts ignition timing by turning the ground path to the coil(s) on and off as necessary.
6. Acceleration Mode
   
   This is an open loop mode. The PCM recognizes an abrupt increase in throttle position or manifold absolute pressure as a demand for increased engine output and vehicle acceleration. The PCM increases injector pulse width in response to increased throttle opening.
7. Deceleration Mode
   
   This is an open loop mode with engine at operating temperature. During hard deceleration, PCM receives inputs from A/C switch, battery voltage, ECT sensor, CKP sensor, IAT sensor, MAP sensor, TP sensor, CMP sensor and VSS signal. PCM will ignore O2 sensor signal and enter a fuel cut-off strategy when vehicle is under hard deceleration with proper RPM and closed throttle conditions. If hard deceleration does not exist, PCM will determine proper injector pulse width. PCM will adjust IAC motor and ignition timing based on above inputs.
8. Wide Open Throttle Mode
   
   This is an open loop mode. PCM receives inputs from battery voltage, CKP sensor, ECT sensor, IAT sensor, MAP sensor, TP sensor and CMP sensor. When PCM senses Wide Open Throttle (WOT), voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off. The PCM ignores the O2 sensor input signal and provides a predetermined amount of additional fuel. This is done by adjusting injector pulse width. The PCM adjusts ignition timing by turning the ground path to the coil(s) on and off.
9. Ignition Switch Off Mode
   
   When ignition switch is turned to OFF position, the PCM stops operating the fuel injectors, ignition coil, ASD relay and fuel pump relay.