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When pump pressure drops to approximately 1379 kPa (200 psi), the switch circuit will re-close and SENSOR RETURN—PCM INPUT OPERATION The Sensor Return circuits are internal to the Pow- ertrain Control Module (PCM). Sensor Return provides a low–noise ground refer- ence for all engine control system sensors. Refer to THROTTLE POSITION SENSOR (TPS)—PCM DESCRIPTION The 3–wire Throttle Position Sensor (TPS) is mounted on the throttle body and is connected to the OPERATION The TPS is a 3–wire variable resistor that provides the Powertrain Control Module (PCM) with an input The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the The PCM needs to identify the actions and position of the throttle blade at all times. This information is • Ignition timing advance • Fuel injection pulse-width • Idle (learned value or minimum TPS) • Off-idle (0.06 volt) • Wide Open Throttle (WOT) open loop (2.608 volts above learned idle voltage) • Deceleration fuel lean out • Fuel cutoff during cranking at WOT (2.608 volts above learned idle voltage) • A/C WOT cutoff (certain automatic transmis- sions only) VEHICLE SPEED AND DISTANCE SENSOR— DESCRIPTION The 3–wire Vehicle Speed Sensor (VSS) is located on the speedometer pinion gear adapter. If equipped of the transfer case (drivers side). If equipped with 2WD, this adapter is located on the OPERATION The VSS is a 3–circuit (3–wire), magnetic, hall-ef- fect sensor. The 3 circuits are: trol Module (PCM). • A ground is provided for the sensor though a low-noise sensor return circuit in the PCM. • An input to the PCM is used to determine vehi- cle speed and distance traveled. The speed sensor generates 8 pulses per sensor revolution. These signals, in conjunction with a Under deceleration conditions, the PCM adjusts the Idle Air Control (IAC) motor to maintain a AUTO SHUTDOWN (ASD) RELAY—PCM DESCRIPTION The 5–pin, 12–volt, Automatic Shutdown (ASD) relay is located in the Power Distribution Center OPERATION The ASD relay supplies battery voltage (12+ volts) to the fuel injectors and ignition coil(s). With certain The ground circuit for the coil within the ASD relay is controlled by the Powertrain Control Module The ASD relay will be shut–down, meaning the 12–volt power supply to the ASD relay will be de-ac- 14 - 34 FUEL SYSTEM XJ DESCRIPTION AND OPERATION (Continued) |