EMISSION CONTROL SYSTEMS
TABLE OF CONTENTS
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ON-BOARD DIAGNOSTICS ...................1 EVAPORATIVE EMISSION CONTROLS ......... 24
ON-BOARD DIAGNOSTICS
TABLE OF CONTENTS
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DESCRIPTION AND OPERATION
EMISSION SYSTEM........................1
MALFUNCTION INDICATOR LAMP (MIL)........2
STATE DISPLAY TEST MODE ................2
CIRCUIT ACTUATION TEST MODE ............2
DIAGNOSTIC TROUBLE CODES ..............2
DIAGNOSTIC TROUBLE CODE
DESCRIPTIONS .........................3
TASK MANAGER—GASOLINE POWERED
ENGINES ONLY ........................16
MONITORED SYSTEMS....................19
TRIP DEFINITION ........................21
COMPONENT MONITORS ..................22
NON-MONITORED CIRCUITS ...............22
HIGH AND LOW LIMITS ....................23
LOAD VALUE............................23
DESCRIPTION AND OPERATION
EMISSION SYSTEM
OPERATION
The Powertrain Control Module (PCM) monitors
many different circuits in the fuel injection, ignition,
emission and engine systems. If the PCM senses a
problem with a monitored circuit often enough to
indicate an actual problem, it stores a Diagnostic
Trouble Code (DTC) in the PCM’s memory. If the
code applies to a non-emissions related component or
system, and the problem is repaired or ceases to
exist, the PCM cancels the code after 40 warm-up
cycles. Diagnostic trouble codes that affect vehicle
emissions illuminate the Malfunction Indicator
(check engine) Lamp. Refer to Malfunction Indicator
Lamp in this section.
Certain criteria must be met before the PCM
stores a DTC in memory. The criteria may be a spe-
cific range of engine RPM, engine temperature,
and/or input voltage to the PCM.
The PCM might not store a DTC for a monitored
circuit even though a malfunction has occurred. This
may happen because one of the DTC criteria for the
circuit has not been met. For example, assume the
diagnostic trouble code criteria requires the PCM to
monitor the circuit only when the engine operates
between 750 and 2000 RPM. Suppose the sensor’s
output circuit shorts to ground when engine operates
above 2400 RPM (resulting in 0 volt input to the
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.
Fig. 1 Data Link (Diagnostic) Connector Location
1 – 16–WAY DATA LINK CONNECTOR
DN EMISSION CONTROL SYSTEMS 25 - 1
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