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When the Check Engine Lamp is illuminated con- stantly with the key on and the engine running,, it t scan tool is the best method for communicating with the ECM POWERTRAIN CONTROL MODULE (PCM) AND The Engine Control Module (ECM) is mounted underneath the left rear seat. The Powertrain Con- The ECM Controller is a pre–programmed, digital computer. It will either directly operate or partially • Speed Control • Speed Control lamp • Fuel Timing Solenoid • Check Engine Light • Glow Plug Relay • Glow Plugs • Glow Plug Lamp • ASD Relay • Air Conditioning • Tachometer • Electric Vacuum Modulator (EVM) changing operating conditions. The ECM receives input signals from various switches and sensors. Based on these inputs, the ECM Inputs are: • Theft Alarm • ASD Relay • Control Sleeve Position Sensor • Fuel Temperature Sensor • Mass Air Flow Sensor • Accelerator Pedal Position Sensor • Engine Coolant Temperature Sensor • Low Idle Position Switch • 5 Volt Supply • Vehicle Speed Sensor • Engine Speed/Crank Position Sensor (rpm) • Needle Movement Sensor • Starter Signal • Brake Switch • Speed Control Switch • Power Ground • Ignition (key) Switch Sense After inputs are received by the ECM and PCM, certain sensors, switches and components are con- • A/C Clutch Relay (for A/C clutch operation) • Speed Control Lamp • ASD Relay • 5 Volts Supply • Fuel Quantity Actuator • Fuel Timing Solenoid • Fuel Shutdown Solenoid • Glow Plug Lamp • Check Engine Lamp (“On/Off” signal) • Electric Vacuum Modulator (EVM) • Glow Plug Relay • Tachometer the ECM controller. PCM inputs are: • Power Ground • 5 Volts Supply • Vehicle Speed Sensor • Water-In-Fuel Sensor • Coolant Temperature Sensor • Low Coolant Sensor • Sensor Return • Fuel Level Sensor • Oil Pressure Sensor • Tachometer Signal • Glow Plug Lamp • Check Engine Lamp (“On/Off” signal) • Brake On/Off Switch • Battery Voltage • ASD Relay • Vehicle Theft Alarm “Ok to Run” signal • Body Control Module CCD Bus (+) • Body Control Module CCD Bus (–) • Scan Tool Data Link Receive • Scan Tool Data Link Transmit • Low Coolant Lamp • Generator Control BOOST / PRESSURE SENSOR The Boost Pressure Sensor is mounted to the top of the intake manifold (Fig. 1). It is a sensor that mea- 14 - 24 FUEL SYSTEM—3.1L DIESEL ENGINE WJ DESCRIPTION AND OPERATION (Continued) 2000 JEEP GRAND CHEROKEE |