Jeep Cherokee (XJ): Powertrain control module (PCM)

DESCRIPTION

The Powertrain Control Module (PCM) is located in the engine compartment (Fig. 1). The PCM is referred to as JTEC.

OPERATION

The PCM operates the fuel system. The PCM is a pre-programmed, triple microprocessor digital computer.

It regulates ignition timing, air-fuel ratio, emission control devices, charging system, certain transmission features, speed control, air conditioning compressor clutch engagement and idle speed. The PCM can adapt its programming to meet changing operating conditions.

The PCM receives input signals from various switches and sensors. Based on these inputs, the PCM regulates various engine and vehicle operations through different system components. These components are referred to as Powertrain Control Module (PCM) Outputs. The sensors and switches that provide inputs to the PCM are considered Powertrain Control Module (PCM) Inputs.

The PCM adjusts ignition timing based upon inputs it receives from sensors that react to: engine rpm, manifold absolute pressure, engine coolant tem perature, throttle position, transmission gear selection (automatic transmission), vehicle speed, power steering pump pressure (2.5L engine only), and the brake switch.

Fig. 1 PCM Location

1 - (3) 32-WAY CONNECTORS
2 - PCM

The PCM adjusts idle speed based on inputs it receives from sensors that react to: throttle position, vehicle speed, transmission gear selection, engine coolant temperature and from inputs it receives from the air conditioning clutch switch and brake switch.

Based on inputs that it receives, the PCM adjusts ignition coil dwell. The PCM also adjusts the generator charge rate through control of the generator field and provides speed control operation.

NOTE: PCM Inputs:

•  A/C request (if equipped with factory A/C)
•  A/C select (if equipped with factory A/C)
•  Auto shutdown (ASD) sense
•  Battery temperature
•  Battery voltage
•  Brake switch
•  CCD bus (+) circuits
•  CCD bus (-) circuits
•  Camshaft position sensor signal
•  Crankshaft position sensor
•  Data link connection for DRB scan tool
•  Engine coolant temperature sensor
•  Extended idle switch (4.0L engine with police package)
•  Fuel level
•  Generator (battery voltage) output
•  Ignition circuit sense (ignition switch in on/off/ crank/run position)
•  Intake manifold air temperature sensor
•  Leak detection pump (switch) sense (if equipped)
•  Manifold absolute pressure (MAP) sensor
•  Oil pressure
•  Oxygen sensors
•  Park/neutral switch (auto. trans. only)
•  Power ground
•  Power steering pressure switch (2.5L engine only)
•  Sensor return
•  Signal ground
•  Speed control multiplexed single wire input
•  Throttle position sensor
•  Vehicle speed sensor

NOTE: PCM Outputs:

•  A/C clutch relay
•  Auto shutdown (ASD) relay
•  CCD bus (+/-) circuits for: speedometer, voltmeter, fuel gauge, oil pressure gauge/lamp, engine temp. gauge and speed control warn. lamp
•  Data link connection for DRB scan tool
•  EGR valve control solenoid (if equipped)
•  EVAP canister purge solenoid
•  Five volt sensor supply (primary)
•  Five volt sensor supply (secondary)
•  Fuel injectors
•  Fuel pump relay
•  Generator field driver (-)
•  Generator field driver (+)
•  Idle air control (IAC) motor
•  Ignition coil
•  Leak detection pump (if equipped)
•  Malfunction indicator lamp (Check engine lamp).

Driven through CCD circuits.

•  Radiator cooling fan relay
•  Speed control vacuum solenoid
•  Speed control vent solenoid
•  Tachometer (if equipped). Driven through CCD circuits.
•  Transmission convertor clutch circuit