Jeep Cherokee 2000 Service Manual - page 1250
usually indicates a problem has been detected some-
where within the fuel system. The DRBIII scan tool
is the best method for communicating with the ECM
and PCM to diagnose faults within the system.
POWERTRAIN CONTROL MODULE (PCM)
DESCRIPTION
On LHD vehicles, the ECM is mounted behind the
lower Instrument Panel to the right of the accelera-
tor pedal (Fig. 1). On RHD vehicles, the ECM is
mounted behind the lower Instrument Panel to the
left of the clutch pedal. The Powertrain Control Mod-
ule (PCM) is mounted in the engine compartment.
(Fig. 2).
The ECM Controller is a pre–programmed, digital
computer. It will either directly operate or partially
regulate the:
•
Speed Control
•
Speed Control lamp
•
Fuel Timing Solenoid
•
Check Engine Light
•
Glow Plug Relay
•
Glow Plugs
•
Glow Plug Lamp
•
ASD Relay
•
Air Conditioning
•
Tachometer
•
Electric Vacuum Modulator (EVM)
The ECM can adapt its programming to meet
changing operating conditions.
The ECM receives input signals from various
switches and sensors. Based on these inputs, the
ECM regulates various engine and vehicle operations
through different system components. These compo-
nents are referred to as ECM Outputs. The sensors
and switches that provide inputs to the ECM are
considered ECM Inputs.
ECM Inputs are:
•
Air Conditioning Selection
•
Theft Alarm
•
ASD Relay
•
Control Sleeve Position Sensor
•
Fuel Temperature Sensor
•
Mass Air Flow Sensor
•
Accelerator Pedal Position Sensor
•
Engine Coolant Temperature Sensor
•
Low Idle Position Switch
•
5 Volt Supply
•
Vehicle Speed Sensor
•
Engine Speed/Crank Position Sensor (rpm)
•
Needle Movement Sensor
•
Starter Signal
•
Brake Switch
•
Speed Control Switch
•
Power Ground
•
Ignition (key) Switch Sense
ECM Outputs:
After inputs are received by the ECM and PCM,
certain sensors, switches and components are con-
trolled or regulated by the ECM and PCM. These are
considered ECM Outputs. These outputs are for:
•
A/C Clutch Relay (for A/C clutch operation)
Fig. 1 ECM Location—LHD
1 – ECM HARNESS CONNECTOR C1
2 – ENGINE CONTROL MODULE (ECM)
3 – ECM HARNESS CONNECTOR C2
4 – ACCELERATOR PEDAL POSITION SENSOR
Fig. 2 PCM Location—LHD
1 – PCM HARNESS CONNECTOR C1
2 – PCM HARNESS CONNECTOR C2
3 – PCM HARNESS CONNECTOR C3
4 – POWERTRAIN CONTROL MODULE (PCM)
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FUEL SYSTEM—2.5L DIESEL ENGINE
XJ
DESCRIPTION AND OPERATION (Continued)