The Powertrain Control Module is best described as a solid state microprocessor, or computer, that controls and monitors a variety of vehicle functions. On the 1999 Ford Expedition, those vehicle functions primarily consisted of the emissions, ignition and fuel injection systems, as well as the automatic transmission.
The 1999 Ford Expedition was available with 4.6-liter and 5.4-liter engines.
On both engines the PCM controlled and monitored the following emissions related components: the Canister Vent Solenoid, Differential Pressure Feedback EGR Sensor, EGR Vaccum Regulator Solenoid, EVAP Canister Purge Valve and the Heated Oxygen Sensors.
The PCM on the 1999 Ford Expedition controlled and monitored the following fuel and ignition related components: The Camshaft Position Sensor, Crankshaft Position Sensor, Cylinder Head Temperature Sensor, Engine Coolant Temperature Sensor, Fuel Injectors, Fuel Pump, Fuel Pump Module, Fuel Pump Relay, Ignition Coils, Inertia Fuel Shut-Off Switch, Intake Air Temperature Sensor, Intake Manifold Tuning Valve and the Knock Sensor.
The PCM on the 1999 Ford Expedition controlled and monitored the following automatic transmission related components: the Automatic Transmission, Brake Pedal Position Switch, Output Shaft Speed Sensor, Transmission Control Switch, Transmission Digital Range Sensor and the Turbine Shaft Speed Sensor.
The PCM on the 1999 Ford Expedition also had direct communication with the Electronic Air Suspension Control Module, the Air Conditioning systems Wide Open Throttle Relay and Air Conditioning Clutch Cycling Pressure Switch, the Speed Control Servo used for Cruise Control and Electronic Suspension systems and the Overhead Tripometer.
The PCM also stores diagnostic trouble codes (DTCs). When the PCM detects a malfunction in the engine management system, it will illuminate the Check Engine Lamp that is typically located on the instrument cluster. An On-Board Diagnostics (OBD) scan tool can be connected to the vehicles sixteen-pin diagnostic connector to read these stored trouble codes and isolate the component, or components at fault.
