Brake switch-pcm input. Engine coolant temperature sensor-pcm input

Brake switch-pcm input


When the brake light switch is activated, the Powertrain Control Module (PCM) receives an input indicating that the brakes are being applied. After receiving this input, the PCM maintains idle speed to a scheduled rpm through control of the Idle Air Control (IAC) motor. The brake switch input is also used to disable vent and vacuum solenoid output signals to the speed control servo.

Engine coolant temperature sensor-pcm input


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.


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

    Dodge Durango (DN) 1998-2003 Service Manual


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