6E–21
3.2L ENGINE DRIVEABILITY AND EMISSIONS
Seral Data Communications
Class II Serial Data Communications
This vehicle utilizes the “Class II” communication system.
Each bit of information can have one of two lengths: long
or short. This allows vehicle wiring to be reduced by
transmitting and receiving multiple signals over a single
wire. The messages carried on Class II data streams are
also prioritized. If two messages attempt to establish
communications on the data line at the same time, only
the message with higher priority will continue. The device
with the lower priority message must wait. The most
significant result of this regulation is that it provides Tech 2
manufacturers with the capability to access data from any
make or model vehicle that is sold.
The data displayed on the other Tech 2 will appear the
same, with some exceptions. Some scan tools will only
be able to display certain vehicle parameters as values
that are a coded representation of the true or actual value.
For more information on this system of coding, refer to
Decimal/Binary/Hexadecimal Conversions. On this
vehicle the Tech 2 displays the actual values for vehicle
parameters. It will not be necessary to perform any
conversions from coded values to actual values.
On-Board Diagnostic (OBD)
On-Board Diagnostic Tests
A diagnostic test is a series of steps, the result of which is
a pass or fail reported to the diagnostic executive. When
a diagnostic test reports a pass result, the diagnostic
executive records the following data:
D
The diagnostic test has been completed since the last
ignition cycle.
D
The diagnostic test has passed during the current
ignition cycle.
D
The fault identified by the diagnostic test is not
currently active.
When a diagnostic test reports a fail result, the diagnostic
executive records the following data:
D
The diagnostic test has been completed since the last
ignition cycle.
D
The fault identified by the diagnostic test is currently
active.
D
The fault has been active during this ignition cycle.
D
The operating conditions at the time of the failure.
Remember, a fuel trim DTC may be triggered by a list of
vehicle faults. Make use of all information available (other
DTCs stored, rich or lean condition, etc.) when
diagnosing a fuel trim fault.
Comprehensive Component Monitor
Diagnostic Operation
Input Components:
Input components are monitored for circuit continuity and
out-of-range values. This includes rationality checking.
Rationality checking refers to indicating a fault when the
signal from a sensor does not seem reasonable,
i.e.Throttle Position (TP) sensor that indicates high
throttle position at low engine loads or BARO voltage.
Input components may include, but are not limited to the
following sensors:
D
Vehicle Speed Sensor (VSS)
D
Inlet Air Temperature (IAT) Sensor
D
Crankshaft Position (CKP) Sensor
D
Throttle Position (TP) Sensor
D
Engine Coolant Temperature (ECT) Sensor
D
Camshaft Position (CMP) Sensor
D
Barometric Pressure (BARO) Sensor
D
Mass Air Flow (MAF) Sensor
In addition to the circuit continuity and rationality check
the ECT sensor is monitored for its ability to achieve a
steady state temperature to enable closed loop fuel
control.
Output Components:
Output components are diagnosed for proper response to
control module commands. Components where
functional monitoring is not feasible will be monitored for
circuit continuity and out-of-range values if applicable.
Output components to be monitored include, but are not
limited to, the following circuit:
D
Idle Air Control (IAC) Motor
D
Control module controlled EVAP Canister Purge Valve
D
Electronic Transmission controls
D
A/C relays
D
Cooling fan relay
D
VSS output
D
MIL control
Refer to ECM and Sensors in General Descriptions.
Passive and Active Diagnostic Tests
A passive test is a diagnostic test which simply monitors a
vehicle system or component. Conversely, an active test,
actually takes some sort of action when performing
diagnostic functions, often in response to a failed passive
test.
Intrusive Diagnostic Tests
This is any on-board test run by the Diagnostic
Management System which may have an effect on
vehicle performance or emission levels.
Warm-Up Cycle
A warm-up cycle means that engine at temperature must
reach a minimum of 70
°
C (160
°
F)
and rise at least 22
°
C
(40
°
F) over the course of a trip.