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Related System Faults
Many of the EOBD system diagnostics will not run if the
engine control module
(ECM) detects a fault on a related system or compo-
nent. One example would be that if the ECM de-
tected a Misfire fault, the diagnostics on the catalytic
converter would be suspended until the Misfire fault was
repaired. If the Misfire fault is severe enough, the cata-
lytic converter can be damaged due to overheating and
will never set a Catalyst DTC until the Misfire fault is re-
paired and the Catalyst diagnostic is allowed to run to
completion. If this happens, the customer may have to
make two trips to the dealership in order to repair the ve-
hicle.
SERIAL DATA COMMUNICATIONS
KWP 2000 Serial Data Communications
Government
regulations require that all vehicle
manufacturers establish a common communication sys-
tem. This vehicle utilizes the "KWP 2000" communica-
tion 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 at-
tempt 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 scan tool manufacturers with the capabil-
ity to access data from any make or model vehicle that is
sold.
The data displayed on the other scan tool 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 val-
ue. On this vehicle, the scan tool displays the actual val-
ues for vehicle parameters. It will not be necessary to
perform any conversions from coded values to actual
values.
ON-BOARD DIAGNOSTIC (EOBD)
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 diag-
nostic 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 cur-
rently active.
When a diagnostic test reports a fail result, the diagnos-
tic executive records the following data:
DAEWOO T-154 BL2,3
ENGINE CONTROLS 1F – 417
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 Diagnostic Trouble Code (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
Comprehensive component monitoring diagnostics are
required to monitor emissions-related input and output
powertrain components.
Input Components
Input components are monitored for circuit continuity
and out-of-range values. This includes rationality check-
ing. 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 Manifold Absolute Pres-
sure (MAP) voltage. Input components may include, but
are not limited to, the following sensors:
D Vehicle Speed Sensor (VSS)
D Crankshaft Position (CKP) sensor
D Throttle Position (TP) sensor
D Engine Coolant Temperature (ECT) sensor
D Camshaft Position (CMP) sensor
D Manifold Absolute Pressure (MAP) 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 con-
trol.
Output Components
Output components are diagnosed for proper response
to control module commands. Components where func-
tional monitoring is not feasible will be monitored for cir-
cuit 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 Evaporative Emission
(EVAP) Canister Purge Valve
D A/C relays
D Cooling fan relay
D VSS output
D MIL control
D Cruise control inhibit
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