Jeep Cherokee (XJ): Five volt sensor supplies-primary and secondary. Fuel level sensor-pcm input. Engine coolant temperature sensor-pcm input

Jeep Cherokee (XJ) 1984 - 2001 Service Manual > Fuel system > Fuel injection system > Description and operation > Five volt sensor supplies-primary and secondary. Fuel level sensor-pcm input. Engine coolant temperature sensor-pcm input

Five volt sensor supplies-primary and secondary

DESCRIPTION

Two different Powertrain Control Module (PCM) five volt supply circuits are used; primary and secondary.

OPERATION

These 2 circuits will:

  •  supply the required 5 volt power source to the Crankshaft Position (CKP) sensor.
  •  supply the required 5 volt power source to the Camshaft Position (CMP) sensor.
  •  supply a reference voltage for the Manifold Absolute Pressure (MAP) sensor.
  •  supply a reference voltage for the Throttle Position Sensor (TPS) sensor.
  •  supply the required 5 volt power source to the oil pressure sensor.
  •  supply the required 5 volt power source for the Vehicle Speed Sensor (VSS) (if equipped).
  • supply the 5 volt power source to the transmission pressure sensor (if equipped with an RE automatic transmission).

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-pcm input

DESCRIPTION

The Engine Coolant Temperature (ECT) sensor is used to sense engine coolant temperature. The sensor protrudes into an engine water jacket.

The ECT sensor is a two-wire Negative Thermal Coefficient (NTC) sensor. Meaning, as engine coolant temperature increases, resistance (voltage) in the sensor decreases. As temperature decreases, resistance (voltage) in the sensor increases.

OPERATION

At key-on, the Powertrain Control Module (PCM) sends out a regulated 5 volt signal to the ECT sensor.

The PCM then monitors the signal as it passes through the ECT sensor to the sensor ground (sensor return).

When the engine is cold, the PCM will operate in Open Loop cycle. It will demand slightly richer airfuel mixtures and higher idle speeds. This is done until normal operating temperatures are reached.

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

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