OPERATION - DATA BUS COMMUNICATION
RECEIVE - PCM INPUT
The PCM uses the SCI communication bus to per-
form engine diagnostics and flash operations. The
PCM uses the J1850 bus to communicate with vari-
ous electronic modules within the vehicle.
OPERATION - IGNITION SENSE - PCM INPUT
The ignition sense input informs the Powertrain
Control Module (PCM) that the ignition switch is in
the off or run position.
OPERATION - PCM GROUND
Ground is provided through multiple pins of the
PCM connector. Depending on the vehicle there may
be as many as two different ground pins. There are
power grounds and sensor grounds.
The power grounds are used to control the ground
side relays, solenoids, ignition coil or injectors. The
signal ground is used for any input that uses sensor
return for ground.
The PCM case is shielded to prevent RFI and EMI.
The PCM case is grounded.
Internally all grounds are connected together, how-
ever there is noise suppression on the sensor ground.
OPERATION
OPERATION
The Powertrain Control Module (PCM) is a digital
computer containing a microprocessor (Fig. 3). The
PCM receives input signals from various switches
and sensors that are referred to as PCM Inputs.
Based on these inputs, the PCM adjusts various
engine and vehicle operations through devices that
are referred to as PCM Outputs.
PCM Inputs:
• A/C Pressure Transducer
• Air Conditioning Controls
• ASD Sense
• Battery Temperature
• Battery voltage
• Brake Switch
• Camshaft Position Sensor
• Crankshaft Position Sensor
• Engine Coolant Temperature Sensor
• Ignition Switch
• Intake Air Temperature Sensor
• J1850 Bus
• Leak Detection Pump Switch
• Manifold Absolute Pressure (MAP) Sensor
• Oil Pressure Sensor
• Oil Temperature Transducer
• Oxygen Sensors
• SCI Receive
• Throttle Position Sensor
• Vehicle Speed Sensor
PCM Outputs:
• Air Conditioning Clutch Relay
• Auto Shutdown (ASD) Relay
• Data Link Connector
• Duty Cycle EVAP Canister Purge Solenoid
• Double Start Override Relay
• Downstream O2 Heater Relay
• Fuel Injectors
• Fuel Pump Relay
• Generator Field Ground Control
• Hydraulic Fan Solenoid Control
• Idle Air Control Motor
• Ignition Coils
• J1850 Bus
• SCI Transmit
• Reverse Gear Lockout Solenoid
• Upstream O2 Heater Control
• 2nd/ 3rd Gear Lockout Solenoid
Based on inputs it receives, the PCM adjusts fuel
injector pulse width, idle speed, ignition spark
advance, ignition coil dwell and EVAP canister purge
operation. The PCM regulates the cooling fan, and
air conditioning. The PCM changes generator charge
rate by adjusting the generator field. The PCM also
performs diagnostics.
The PCM adjusts injector pulse width (air-fuel
ratio) based on the following inputs.
• Battery voltage
• Coolant temperature
• Intake air temperature
• Exhaust gas content (oxygen sensor)
• Engine speed (crankshaft position sensor)
• Manifold absolute pressure
• Throttle position
Fig. 3 PCM LOCATION
ZB ELECTRONIC CONTROL MODULES 8E - 5
POWERTRAIN CONTROL MODULE (Continued)
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