Jeep Cherokee 2000 Service Manual - Emission Control System
EMISSION CONTROL SYSTEM
TABLE OF CONTENTS
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ON-BOARD DIAGNOSTICS—2.5L DIESEL
ENGINE
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EXHAUST EMISSION CONTROLS—2.5L
DIESEL ENGINE. . . . . . . . . . . . . . . . . . . . . . . . . . . 6
ON-BOARD DIAGNOSTICS—2.5L DIESEL ENGINE
TABLE OF CONTENTS
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DESCRIPTION AND OPERATION
EMISSION CONTROL SYSTEM—2.5L DIESEL
ENGINE
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DIAGNOSTIC TROUBLE CODES . . . . . . . . . . . . . . 2
DESCRIPTION AND OPERATION
EMISSION CONTROL SYSTEM—2.5L DIESEL
ENGINE
DESCRIPTION
The 2.5L diesel Engine Control Module (ECM) and
Powertrain Control Module (PCM) monitor and con-
trol many different circuits in the fuel injection pump
and engine systems. If the ECM senses a problem
with a monitored circuit that indicates an actual
problem, a Diagnostic Trouble Code (DTC) will be
stored in the PCM’s memory, and eventually may
illuminate the Check Engine Lamp constantly while
the key is on. If the problem is repaired, or is inter-
mittent, the ECM will erase the DTC after 40
warm-up cycles without the the fault detected. A
warm-up cycle consists of starting the vehicle when
the engine is cold, then the engine is warmed up to a
certain temperature, and finally, the engine tempera-
ture falls to a normal operating temperature, then
the key is turned off.
Certain criteria must be met for a DTC to be
entered into ECM memory. The criteria may be a
specific range of engine rpm, engine or fuel tempera-
ture and/or input voltage to the ECM. A DTC indi-
cates that the ECM has identified an abnormal
signal in a circuit or the system. A DTC may indicate
the result of a failure, but never identify the failed
component directly.
There are several operating conditions that the
ECM does not monitor and set a DTC for. Refer to
the following Monitored Circuits and Non–Monitored
Circuits in this section.
ECM MONITORED SYSTEMS
The ECM can detect certain problems in the elec-
trical system.
Open or Shorted Circuit – The ECM will not
distinguish between an open or a short to ground,
however the ECM can determine if the circuit is
shorted to voltage.
Output Device Current Flow – The ECM senses
whether the output devices are electrically connected.
If there is a problem with the circuit, the ECM
senses whether the circuit is open, shorted to ground
(–), or shorted to (+) voltage.
ECM NON–MONITORED SYSTEMS
The ECM does not monitor the following circuits,
systems or conditions that could have malfunctions
that result in driveability problems. A DTC will not
be displayed for these conditions.
Fuel Pressure: Fuel pressure is controlled by the
fuel injection pump. The ECM cannot detect fuel
pressure problems in this component. The ECM does
a comparison analysis of fuel quantity, fuel timing,
fuel temperature, and control sleeve sensor inputs to
determine if a fuel problem exists.
Cylinder Compression: The ECM cannot detect
uneven, low, or high engine cylinder compression.
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EMISSION CONTROL SYSTEM
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