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• supply the 5 volt power source to the transmis- sion pressure sensor (if equipped with an RE auto- FUEL LEVEL SENSOR—PCM INPUT DESCRIPTION The fuel level sensor (fuel gauge sending unit) is located on the fuel pump module. OPERATION Refer to Fuel Gauge Sending Unit in the Fuel Delivery section for information. ENGINE COOLANT TEMPERATURE SENSOR— DESCRIPTION The Engine Coolant Temperature (ECT) sensor is used to sense engine coolant temperature. The sensor The ECT sensor is a two-wire Negative Thermal Coefficient (NTC) sensor. Meaning, as engine coolant OPERATION At key-on, the Powertrain Control Module (PCM) sends out a regulated 5 volt signal to the ECT sensor. When the engine is cold, the PCM will operate in Open Loop cycle. It will demand slightly richer air- The PCM uses inputs from the ECT sensor for the following calculations: • for engine coolant temperature gauge operation through CCD or PCI (J1850) communications • Injector pulse-width • Spark-advance curves • ASD relay shut-down times • Idle Air Control (IAC) motor key-on steps • Pulse-width prime-shot during cranking • O2 sensor closed loop times • Purge solenoid on/off times • EGR solenoid on/off times (if equipped) • Leak Detection Pump operation (if equipped) • Radiator fan relay on/off times (if equipped) • Target idle speed EXTENDED IDLE SWITCH—PCM INPUT DESCRIPTION USED ONLY WITH OPTIONAL POLICE PACKAGE WHEN EQUIPPED WITH A 4.0L OPERATION The extended idle switch is used to raise the engine idle speed to approximately 1000 rpm by sup- OXYGEN SENSOR—PCM INPUT DESCRIPTION The Oxygen Sensors (O2S) are attached to, and protrude into the vehicle exhaust system. Depending OPERATION An O2 sensor is a galvanic battery that provides the PCM with a voltage signal (0-1 volt) inversely adjust injector pulse-width to achieve the 14.7–to–1 air/fuel ratio necessary for proper engine An O2 sensor must have a source of oxygen from outside of the exhaust stream for comparison. Cur- Four wires (circuits) are used on each O2 sensor: a 12–volt feed circuit for the sensor heating element; a Oxygen Sensor Heaters/Heater Relays: On a certain non-California emission package, the heaters 14 - 30 FUEL SYSTEM XJ DESCRIPTION AND OPERATION (Continued) |