Operation

POWERTRAIN CONTROL MODULE

The primary function of the Powertrain Control Module (PCM) is to operate the following systems:

- Fuel Delivery and Injection
- Electronic Throttle Control
- Ignition
- Secondary Air Injection and Emission Control
- Idle Speed Control
- Engine Cooling Fans
- Starting

The secondary function of the PCM is to provide on-board diagnostics. During engine operation, the PCM monitors engine sensors and their related circuits for signals that are out of the normal range. The PCM constantly compares input signal voltages from each sensor with pre-programmed values (the established high and low limits of the input sensor range). If the input signal voltage is not within the established high and low limits of the input sensor range, a Diagnostic Trouble Code (DTC) will be stored (set) in the ECM memory, where it can be displayed or cleared with a scan tool. If a DTC is related to the engine or emission system, the ECM will send a signal to illuminate the Malfunction Indicator Light (MIL) in the instrument cluster module. Each monitored circuit has an associated set of conditions that the PCM must detect before a DTC will set. It is possible that a DTC for a monitored circuit may not set, even though a malfunction has occurred. This can happen if all conditions for setting the DTC have not occurred. If a DTC is cleared with a scan tool and the conditions that caused it have not been corrected, the DTC will continue to set.

PCM Inputs

The PCM is programmed to adaptively control engine systems based on the inputs received from the following engine system sensors:

- Fuel Rail Pressure Sensor
- Boost Pressure Sensor
- Coolant Temperature Sensor
- Charge Air Temperature Sensor
- Intake Manifold Pressure Sensor
- Accelerator Pedal Sensor
- Crankshaft Position Sensor
- Fuel Temperature Sensor
- Transmission Shifter Position

PCM Outputs

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 also determines the appropriate transmission shift schedule and shift points, depending on the present operating conditions and driver demand. The PCM regulates the cooling fan, air conditioning and speed control systems. 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
- Exhaust gas content (oxygen sensor)
- Engine speed (crankshaft position sensor)
- Intake air temperature
- Manifold absolute pressure
- Throttle position

The PCM adjusts ignition timing, intake manifold runner position, and variable valve timing based on the following inputs.

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

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

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

The camshaft position sensor and crankshaft position sensor signals are sent to the PCM. If the PCM does not receive the signal within approximately 1 second of engine cranking, it deactivates the fuel pump. When these are deactivated, power is shut off to the fuel injectors, ignition coils, oxygen sensor heating elements and fuel pump.

The PCM contains a voltage converter that changes battery voltage to a regulated 5 volts direct current to power the camshaft position sensor, crankshaft position sensor, manifold absolute pressure sensor, throttle position sensor, A/C pressure switch, A/C pressure transducer, and vehicle speed sensor.