Jeep Cherokee (XJ): Throttle position sensor (tps)-pcm input. Vehicle speed and distance sensor- pcm input. Auto shutdown (asd) relay-pcm output

Jeep Cherokee (XJ) 1984 - 2001 Service Manual > Fuel system > Fuel injection system > Description and operation > Throttle position sensor (tps)-pcm input. Vehicle speed and distance sensor- pcm input. Auto shutdown (asd) relay-pcm output

Throttle position sensor (tps)-pcm input


The 3-wire Throttle Position Sensor (TPS) is mounted on the throttle body and is connected to the throttle blade.


The TPS is a 3-wire variable resistor that provides the Powertrain Control Module (PCM) with an input signal (voltage) that represents the throttle blade position of the throttle body. The sensor is connected to the throttle blade shaft. As the position of the throttle blade changes, the resistance (output voltage) of the TPS changes.

The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the PCM) represents the throttle blade position. The PCM receives an input signal voltage from the TPS.

This will vary in an approximate range of from.26 volts at minimum throttle opening (idle), to 4.49 volts at wide open throttle. Along with inputs from other sensors, the PCM uses the TPS input to determine current engine operating conditions. In response to engine operating conditions, the PCM will adjust fuel injector pulse width and ignition timing.

The PCM needs to identify the actions and position of the throttle blade at all times. This information is needed to assist in performing the following calculations:

  •  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 transmissions only)

Vehicle speed and distance sensor- pcm input


The 3-wire Vehicle Speed Sensor (VSS) is located on the speedometer pinion gear adapter. If equipped with 4WD, this adapter is located on the extension housing of the transfer case (drivers side). If equipped with 2WD, this adapter is located on the left side of the transmission extension housing.


The VSS is a 3-circuit (3-wire), magnetic, hall-effect sensor.

The 3 circuits are:

  •  A 5-volt power supply from the Powertrain Control 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 vehicle speed and distance traveled.

The speed sensor generates 8 pulses per sensor revolution. These signals, in conjunction with a closed throttle signal from the throttle position sensor, indicate a closed throttle deceleration to the PCM. When the vehicle is stopped at idle, a closed throttle signal is received by the PCM (but a speed sensor signal is not received).

Under deceleration conditions, the PCM adjusts the Idle Air Control (IAC) motor to maintain a desired MAP value. Under idle conditions, the PCM adjusts the IAC motor to maintain a desired engine speed.

Auto shutdown (asd) relay-pcm output


The 5-pin, 12-volt, Automatic Shutdown (ASD) relay is located in the Power Distribution Center (PDC). Refer to label on PDC cover for relay location.


The ASD relay supplies battery voltage (12+ volts) to the fuel injectors and ignition coil(s). With certain emissions packages it also supplies 12-volts to the oxygen sensor heating elements.

The ground circuit for the coil within the ASD relay is controlled by the Powertrain Control Module (PCM). The PCM operates the ASD relay by switching its ground circuit on and off.

The ASD relay will be shut-down, meaning the 12-volt power supply to the ASD relay will be de-activated by the PCM if:

  • the ignition key is left in the ON position. This is if the engine has not been running for approximately 1.8 seconds.
  •  there is a crankshaft position sensor signal to the PCM that is lower than pre-determined values. The PCM will sense if or when the ASD relay has been activated through a "sense circuit". Refer to Automatic Shut-Down (ASD) Relay Sense-PCM Input for additional information.

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