Neon, 2000 - 2005

Description & Operation (16 of 19)


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The Powertrain Control Module (PCM) is a digital computer containing a microprocessor. 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. Location of the PCM on 2.0L engines

PCM Ground

Ground is provided through multiple pins of the PCM connector. Depending on the vehicle there may be as many as three different ground pins. There are power grounds and sensor grounds.

The power grounds are used to control the ground side of any relay, solenoid, ignition coil or injector. The signal ground is used for any input that uses sensor return for ground, and the ground side of any internal processing component.

The SBEC III case is shielded to prevent RFI and EMI. The PCM case is grounded and must be firmly attached to a good clean body ground.

Internally all grounds are connected together, however there is noise suppression on the sensor ground. For EMI and RFI protection the case is also grounded separately from the ground pins.

PCM Inputs

Air Conditioning Controls
Battery Voltage
Inlet Air/Battery Temperature Sensor
Brake Switch
Camshaft Position Sensor
Crankshaft Position Sensor
Engine Coolant Temperature Sensor
Fuel Level Sensor
Ignition Switch
Inlet Air/Intake Air Temperature Sensor
Knock Sensor
Manifold Absolute Pressure (MAP) Sensor
Oxygen Sensors
Power Steering Pressure Switch
SCI Receive
Speed Control Switches
Throttle Position Sensor
Transmission Park/Neutral Switch (automatic transmission)
Vehicle Speed Sensor

PCM Outputs

Air Conditioning WOT Relay
Auto Shutdown (ASD) Relay
Charging Indicator Lamp
Data Link Connector
Proportional Purge Solenoid
EGR Solenoid
Fuel Injectors
Fuel Pump Relay
Generator Field
Idle Air Control Motor
Ignition Coils
Malfunction Indicator (Check Engine) Lamp
Radiator Fan Relay
Speed Control Solenoids
Torque Converter Clutch 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, air conditioning and speed control systems, and 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
Inlet Air/Intake air temperature
Exhaust gas content (oxygen sensor)
Engine speed (crankshaft position sensor)
Manifold absolute pressure
Throttle position

The PCM adjusts ignition timing based on the following inputs:

Coolant temperature
Inlet Air/Intake air temperature
Engine speed (crankshaft position sensor)
Knock sensor
Manifold absolute pressure
Throttle position
Transmission gear selection (park/neutral switch)

The PCM also adjusts engine idle speed through the idle air control motor based on the following inputs:

Air conditioning sense
Battery voltage
Battery temperature
Brake switch
Coolant temperature
Engine speed (crankshaft position sensor)
Engine run time
Manifold absolute pressure
Power steering pressure switch
Throttle position
Transmission gear selection (park/neutral switch)
Vehicle distance (speed)

The crankshaft position sensor signal is sent to the PCM. If the PCM does not receive the signal within approximately one second of engine cranking, it deactivates the ASD relay and fuel pump relay. When these relays deactivate, power is shut off from the fuel injectors, ignition coils, heating element in the oxygen sensors and the fuel pump.

The PCM contains a voltage converter that changes battery voltage to a regulated 8 volts direct current to power the camshaft position sensor, crankshaft position sensor and vehicle speed sensor. The PCM also provides a 5-volt direct current supply for the manifold absolute pressure sensor and throttle position sensor.