PCM). Because the condition happens at an engine
speed above the maximum threshold (2000 rpm), the
PCM will not store a DTC.
There are several operating conditions for which
the PCM monitors and sets DTC’s. Refer to Moni-
tored Systems, Components, and Non-Monitored Cir-
cuits in this section.
NOTE: Various diagnostic procedures may actually
cause a diagnostic monitor to set a DTC. For
instance, pulling a spark plug wire to perform a
spark test may set the misfire code. When a repair
is completed and verified, use the DRB III scan tool
to erase all DTC’s and extinguish the MIL.
Technicians can display stored DTC’s by using the
DRB III scan tool. Refer to Diagnostic Trouble Codes
in this section. For DTC information, refer to charts
in this section.
MALFUNCTION INDICATOR LAMP (MIL)
DESCRIPTION
The data link connector is located at the lower
edge of the instrument panel near the steering col-
umn.
OPERATION
As a functional test, the Malfunction Indicator
Lamp (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 illuminates the MIL. If a
problem is detected, the PCM sends a message over
the CCD Bus to the instrument cluster to illuminate
the lamp. The PCM illuminates the MIL only for
DTC’s that affect vehicle emissions. The MIL stays
on continuously when the PCM has entered a
Limp-In mode or identified a failed emission compo-
nent or system. The MIL remains on until the DTC
is erased. 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.
DRB III 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. From
the state display screen, access either State Display
Inputs and Outputs or State Display Sensors.
DRB III 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.
DIAGNOSTIC TROUBLE CODES
DESCRIPTION
A Diagnostic Trouble Code (DTC) indicates the
PCM has recognized an abnormal condition in the
system.
Fig. 1 Data Link (Diagnostic) Connector
1 – DIAGNOSTIC CONNECTOR
25 - 2
EMISSION CONTROL SYSTEMS
NS
DESCRIPTION AND OPERATION (Continued)
