- PCM -
MAIN OPERATIONS
Continued from Part 1
MAIN OPERATIONS
Continued from Part 1
ENGINE WARM-UP MODE: This is an Open Loop mode.
During engine warm-up, the PCM receives inputs from:
1. Direct Battery voltage
2. Crankshaft position sensor
3. Engine coolant temperature sensor
4. Intake manifold air temperature sensor
5. Manifold absolute pressure (MAP) sensor
6. Throttle position sensors (TPS)
7. Camshaft position sensor signal
8. Park/neutral switch (gear indicator signal)
9. Pedal Value Sensors (PVS)
10. Air conditioning select signal (if equipped)
11. Air conditioning request signal (if equipped)
Based on these inputs the following occurs:
1. 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.
2. The PCM adjusts engine idle speed through the electronic throttle control (ETC) motor and adjusts ignition timing accordingly.
3. The PCM operates the A/C compressor clutch through the clutch relay. This is done if A/C has been selected by the vehicle operator and requested by the A/C thermostat.
4. When engine has reached operating temperature, the PCM will begin monitoring O2S sensor to control the air/fuel ratio. The system will then leave the warm-up mode and go into closed loop operation.
IDLE MODE:
When the engine is at operating temperature, this is a Closed Loop mode.
At idle speed, the PCM receives inputs from:
1. Air conditioning select signal (if equipped)
2. Air conditioning request signal (if equipped)
3. Battery voltage
4. Crankshaft position sensor
5. Engine coolant temperature sensor
6. Intake manifold air temperature sensor
7. Manifold absolute pressure (MAP) sensor
8. Pedal Value Sensors (PVS)
9. Throttle position sensors (TPS)
10. Camshaft position sensor signal
11. Battery voltage
12. Park/neutral switch (gear indicator signal)
13. Oxygen sensors
Based on these inputs, the following occurs:
1. 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.
2. The PCM monitors the O2S sensor input and adjusts air-fuel ratio by varying injector pulse width. It also adjusts engine idle speed through the electronic throttle control (ETC) motor.
3. The PCM adjusts ignition timing by increasing and decreasing spark advance.
4. The PCM operates the A/C compressor clutch through the A/C clutch relay. This happens if A/C has been selected by the vehicle operator and requested by the A/C thermostat.
CRUISE MODE:
When the engine is at operating temperature, this is a Closed Loop mode.
At cruising speed, the PCM receives inputs from:
1. Air conditioning select signal (if equipped)
2. Air conditioning request signal (if equipped)
3. Battery voltage
4. Engine coolant temperature sensor
5. Crankshaft position sensor
6. Intake manifold air temperature sensor
7. Manifold absolute pressure (MAP) sensor
8. Pedal Value Sensors (PVS)
9. Throttle position sensors (TPS)
10. Camshaft position sensor signal
11. Park/neutral switch (gear indicator signal)
12. Oxygen (O2S) sensors
Based on these inputs, the following occurs:
1. Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then adjust the injector pulse width by turning the ground circuit to each individual injector on and off.
2. The PCM monitors the O2S sensor input and adjusts air-fuel ratio.
3. The PCM adjusts ignition timing by turning the ground path to the coils on and off.
4. The PCM operates the A/C compressor clutch through the clutch relay. This happens if A/C has been selected by the vehicle operator and requested by the A/C thermostat.
ACCELERATION MODE:
This is an Open Loop mode. The PCM recognizes an abrupt increase in throttle position or MAP pressure
as a demand for increased engine output and vehicle acceleration. The PCM increases injector pulse width
in response to increased throttle opening.
DECELERATION MODE:
When the engine is at operating temperature, this is an Open Loop mode.
During hard deceleration, the PCM receives the following inputs.
1. Air conditioning select signal (if equipped)
2. Air conditioning request signal (if equipped)
3. Battery voltage
4. Engine coolant temperature sensor
5. Crankshaft position sensor
6. Intake manifold air temperature sensor
7. Manifold absolute pressure (MAP) sensor
8. Pedal Value Sensors (PVS)
9. Throttle position sensors (TPS)
10. Camshaft position sensor signal
11. Park/neutral switch (gear indicator signal)
12. Vehicle speed
If the vehicle is under hard deceleration with the proper rpm and closed throttle conditions, the PCM
will ignore the oxygen sensor input signal. The PCM will enter a fuel cut-off strategy in which it will
not supply a ground to the injectors. If a hard deceleration does not exist, the PCM will determine the
proper injector pulse width and continue injection.
The PCM adjusts ignition timing by turning the ground path to the coils on and off.
WIDE OPEN THROTTLE MODE (WOT)
This is an Open Loop mode. During wide open throttle operation, the PCM receives the following inputs.
1. Battery voltage
2. Crankshaft position sensor
3. Engine coolant temperature sensor
4. Intake manifold air temperature sensor
5. Manifold absolute pressure (MAP) sensor
6. Pedal Value Sensors (PVS)
7. Throttle position sensors (TPS)
8. Camshaft position sensor signal
During wide open throttle conditions, the following occurs:
1. 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 ignores the oxygen sensor input signal and provides a predetermined amount of additional fuel. This is done by adjusting injector pulse width.
2. The PCM adjusts ignition timing by turning the ground path to the coil on and off.
OPERATION - IGNITION CIRCUIT SENSE
When the ignition key is inserted, the position of the key is transmitted via the CAN bus to
Integrated Power Module (IPM). When the key position is rotated to the ACC position or
Run/Start position, the IPM energizes the Ignition ACC and/or Run/Start feed which will
wake up the Powertrain Control Module (PCM) accordingly.
These feeds are essentially fused switched battery voltage feeds fabricated by the IPM with
relays or solid state devices. There is not Ignition Start feed to the PCM - this is handled by
a CAN bus message from IPM to PCM. NOTE: Only on those applications with the 42RLE
does the PCM receive an Ignition ACC feed.
IGNITION SWITCH OFF MODE
When ignition switch is turned to OFF position, the PCM stops operating the injectors, ignition
coil, ASD relay and fuel pump relay.
This touches on just some of the basic functions of our PCM.
IF there is interest, I will continue with another added post on the very extensive emissions criteria that the PCM meets.
It is just as elaborate if not more sophisticated on active and passive monitoring of engine components to meet all
Federal emissions standards.
Happy Modding!
