- PCM -
Many of these operations are identical on both the 5.7L and the 6.1L HEMI engines. (2008-09)
The PCM operates the fuel system. The PCM is a pre-programmed, dual microprocessor digital
computer. It regulates ignition timing, air-fuel ratio, emission control devices, charging system,
certain transmission features, speed control, air conditioning compressor clutch engagement and
The PCM can "adapt" its programming to meet changing operating conditions. These conditions
are stored over a short (quick learn) or longer (standard learn) "start cycle" engine periods.
The PCM has two main "modes of operation" and that will be discussed further down.
The PCM receives input signals from various switches and sensors. Based on these inputs, the
PCM regulates various engine and vehicle operations through different system components.
These components are referred to as Powertrain Control Module (PCM) Outputs.
The sensors and switches that provide inputs to the PCM are considered Powertrain Control Module
The PCM adjusts ignition timing based upon inputs it receives from sensors that react to:
Engine rpm, manifold absolute pressure, engine coolant temperature, throttle position, pedal
value, transmission gear selection (automatic transmission), vehicle speed and the brake switch.
The PCM adjusts idle speed based on inputs it receives from sensors that react to: throttle
position, vehicle speed, transmission gear selection, engine coolant temperature and from
inputs it receives from the air conditioning clutch switch and brake switch.
Based on inputs that it receives, the PCM adjusts ignition coil dwell. The PCM also adjusts the
generator charge rate through control of the generator field and provides speed control operation.
1. A/C select AND request via CAN communication bus
2. Auto shutdown (ASD) sense
3. Brake switches 1 AND 2
4. Direct Battery voltage
5. EGR Position sensor
6. EVAP purge solenoid current sense
7. Camshaft position sensor signal
8. Crankshaft position sensor
9. CAN C bus communication for internal module communication and ata link connection for scan tools
10. Engine coolant temperature sensor
11. 5 volts (primary)
12. 5 volts (secondary)
13. Fuel level via CAN communication bus from IPM
14. Generator (battery voltage sense) output
15. Ignition circuit sense (ACC AND Run/Start via hardwire from the Total Integrated Power Module (TIPM) while the Crank indication is
via CAN communication bus)
16. Intake manifold air temperature sensor
17. Evaporative system ESIM vacuum switch (if equipped)
18. Manifold absolute pressure (MAP) sensor
19. Oil pressure
20. Oxygen sensors signals
21. Park/neutral switch
22. Power ground
23. Sensor return
24. Signal ground
25. Speed control switch states are determined by SCM and transmitted over the bus via CAN bus
26. SRV position sensor signal
27. Throttle position sensors and Pedal value sensors
28. Transmission pressure switch inputs (42RLE)
29. Transmission variable line pressure sensor (42RLE)
30. Transmission temperature sensor (42RLE)
31. Vehicle speed (ABS equipped) via CAN C bus from ABS module
1. Vehicle Speed (Non-ABS) from IPM via CAN C and Trans Turbine sensors (with pinion factor)
2. A/C clutch relay
3. Auto shutdown (ASD) relay coil
4. CAN C bus messages for speedometer (non-ABS packages), voltmeter or generator lamp (if equipped), fuel gauge,
5 oil pressure gauge/lamp, engine coolant temperature gauge and speed control indication warning lamp
6. CAN bus communication for inter module communication and data link connection for scan tools
7. EGR valve control solenoid (if equipped)
8. Electronic Throttle Control (ETC) motor
9. EVAP Purge solenoid
10. Fuel injectors
11. Fuel pump relay
12. Generator field driver
13. Ignition coils
14. Malfunction indicator lamp (also known as MIL). Driven through CAN-Bus Messages.
15. Oxygen sensor heater elements
16. Radiator cooling fan relay via CAN-Bus message to TIPM
17. Short Runner Valve (SRV) actuator (if equipped)
18. Tachometer (if equipped). Driven through Bus Messages.
19. Transmission solenoids (42RLE only)
20. Transmission power relay
PCM (Powertrain Control Module)MODES OF OPERATION
also called NGC
also called NGC
As input signals to the Powertrain Control Module (PCM) change, the PCM adjusts its response to the
output devices. For example, the PCM must calculate different injector pulse width and ignition timing
for idle than it does for wide open throttle (WOT).
The PCM will operate in two different modes:
1. Open Loop
2. Closed Loop.
During Open Loop modes, the PCM receives input signals and responds only according to preset
PCM programming. Input from the oxygen (O2S) sensors is not monitored during Open Loop modes.
During Closed Loop modes, the PCM will monitor the oxygen (O2S) sensors input. This input indicates
to the PCM whether or not the calculated injector pulse width results in the ideal air-fuel ratio. This ratio
is 14.7 parts air-to-1 part fuel.
By monitoring exhaust oxygen content through the O2S sensor, the PCM can fine tune the injector pulse
width. This is done to achieve optimum fuel economy combined with low emission engine performance.
The fuel injection system has the following modes of operation:
1. Ignition switch ON
2. Engine start-up (crank)
3. Engine warm-up
8. Wide open throttle (WOT)
9. Ignition switch OFF
The ignition switch On, engine start-up (crank), engine warm-up, acceleration, deceleration and
wide open throttle (WOT) modes are Open Loop modes. The idle and cruise modes, (with the
engine at operating temperature) are Closed Loop modes.
IGNITION SWITCH (KEY-ON) MODE:
This is an Open Loop mode.
When the fuel system is activated by the ignition switch, the following actions occur:
1. The PCM determines atmospheric air pressure from the MAP sensor input to determine basic fuel strategy.
2. The PCM monitors the engine coolant temperature sensor input. The PCM modifies fuel strategy based on this input.
3. Intake manifold air temperature sensor input is monitored.
4. Throttle position sensors (TPS) and pedal value sensors are monitored.
5. The auto shutdown (ASD) relay is energized by the PCM for approximately three seconds.
6. The fuel pump is energized through the fuel pump relay by the PCM. The fuel pump will operate for approximately three seconds unless the engine is operating or the starter motor is engaged.
7. The O2S sensor heater element is energized via the O2S heater drivers (solid state devices) internal to the PCM. These drivers provide a PWM 0-12V signal to heat the O2S heater elements to optimize the O2S sensor signal output. The O2S sensor input is not used by the PCM to calibrate air-fuel ratio during this mode of operation.
ENGINE START-UP MODE:
This is an Open Loop mode. The following actions occur when the starter motor is engaged.
The PCM receives inputs from:
1. Direct Battery voltage
2. Pedal Value Sensors (PVS)
3. Engine coolant temperature sensor
4. Crankshaft position sensor
5. Intake manifold air temperature sensor
6. Manifold absolute pressure (MAP) sensor
7. Throttle position sensors (TPS)
8. Camshaft position sensor signal
The PCM monitors the crankshaft position sensor. If the PCM does not receive a crankshaft position
sensor signal within approximately 3 seconds of cranking the engine, it will shut down the fuel injection
The fuel pump is activated by the PCM through the fuel pump relay located in the TIPM.
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 actuating ground circuit to each
individual injector on and off.
The PCM determines the proper ignition timing according to input received from the crankshaft
(End of Part 1 of 2)