Jeep Cherokee 2000 Service Manual - page 1920
MALFUNCTION INDICATOR LAMP (MIL)
DESCRIPTION
The Malfunction Indicator Lamp (MIL) is located
on the instrument panel. It is displayed as an engine
icon (graphic).
OPERATION
As a functional test, the MIL illuminates at key-on
before engine cranking. Whenever the Powertrain
Control Module (PCM) sets a Diagnostic Trouble
Code (DTC) that affects vehicle emissions, it illumi-
nates the MIL. If a problem is detected, the PCM
sends a message to the instrument cluster to illumi-
nate the lamp. The PCM illuminates the MIL only
for DTC’s that affect vehicle emissions. There are
some monitors that may take two consecutive trips,
with a detected fault, before the MIL is illuminated.
The MIL stays on continuously when the PCM has
entered a Limp-In mode or identified a failed emis-
sion component. Refer to the Diagnostic Trouble Code
charts in this group for emission related codes.
Also, the MIL either flashes or illuminates contin-
uously when the PCM detects active engine misfire.
Refer to Misfire Monitoring in this section.
Additionally, the PCM may reset (turn off) the MIL
when one of the following occur:
•
PCM does not detect the malfunction for 3 con-
secutive trips (except misfire and Fuel system Moni-
tors).
•
PCM does not detect a malfunction while per-
forming three successive engine misfire or fuel sys-
tem tests. The PCM performs these tests while the
engine is operating within
6
375 RPM of and within
10 % of the load of the operating condition at which
the malfunction was first detected.
STATE DISPLAY TEST MODE
OPERATION
The switch inputs to the Powertrain Control Mod-
ule (PCM) have two recognized states; HIGH and
LOW. For this reason, the PCM cannot recognize the
difference between a selected switch position versus
an open circuit, a short circuit, or a defective switch.
If the State Display screen shows the change from
HIGH to LOW or LOW to HIGH, assume the entire
switch circuit to the PCM functions properly. Connect
the DRB scan tool to the data link connector and
access the state display screen. Then access either
State Display Inputs and Outputs or State Display
Sensors.
CIRCUIT ACTUATION TEST MODE
OPERATION
The Circuit Actuation Test Mode checks for proper
operation of output circuits or devices the Powertrain
Control Module (PCM) may not internally recognize.
The PCM attempts to activate these outputs and
allow an observer to verify proper operation. Most of
the tests provide an audible or visual indication of
device operation (click of relay contacts, fuel spray,
etc.). Except for intermittent conditions, if a device
functions properly during testing, assume the device,
its associated wiring, and driver circuit work cor-
rectly. Connect the DRB scan tool to the data link
connector and access the Actuators screen.
DIAGNOSTIC TROUBLE CODES
OPERATION
A Diagnostic Trouble Code (DTC) indicates that the
Powertrain Control Module (PCM) has recognized an
abnormal condition in the system.
DTC’s are the results of a system or circuit
failure, but do not directly identify the failed
component or components.
Technicians must retrieve stored DTC’s by connect-
ing the DRB III scan tool (or an equivalent scan tool)
to the 16–way data link connector. This connector is
located on the lower edge of the instrument panel
near the steering column.
OBTAINING DTC’s
WARNING: APPLY
PARKING
BRAKE
AND/OR
BLOCK WHEELS BEFORE PERFORMING ANY TEST
ON AN OPERATING ENGINE.
Fig. 1 Data Link (Diagnostic) Connector Location
1 – 16–WAY DATA LINK CONNECTOR
25 - 2
EMISSION CONTROL SYSTEMS
XJ
DESCRIPTION AND OPERATION (Continued)