Daewoo Nubira User Manual page 612

is sent to the powertrain control module (PCM)/engine
control module (ECM). The PCM/ECM then adjusts the
ignition timing to reduce the spark knock.
G SENSOR
The powertrain control module (PCM)/engine control
module (ECM) receives rough road information from the
G sensor. The PCM/ECM uses the rough road information
to enable or disable the misfire diagnostic. The misfire
diagnostic can be greatly affected by crankshaft speed
variations caused by driving on rough road surfaces. The
G sensor generates rough road information by producing
a signal which is proportional to the movement of a small
metal bar inside the sensor.
If a fault occurs which causes the PCM/ECM to not receive
rough road information between 30 and 80 mph (50 and
132 km/h), DTC P1391 will set.
FUEL CUTOFF SWITCH
The fuel cutoff switch is a safety device. In the event of a
collision or sudden impact, it automatically cuts off the fuel
supply and activates the door lock relay. After the switch
has been activated, it must be reset in order to restart the
engine. To reset this fuel–cutoff feature, press the rubber
top of the switch located near the left side of the driver's
seat.
STRATEGY–BASED DIAGNOSTICS
Strategy–Based Diagnostics
The strategy–based diagnostic is a uniform approach to
repair all Electrical/Electronic (E/E) systems. The diag-
nostic flow can always be used to resolve an E/E system
problem and is a starting point when repairs are neces-
sary. The following steps will instruct the technician on
how to proceed with a diagnosis:
S
Verify the customer complaint. To verify the cus-
tomer complaint, the technician should know the
normal operation of the system.
S
Perform preliminary checks as follows:
S Conduct a thorough visual inspection.
S Review the service history.
S Detect unusual sounds or odors.
S Gather Diagnostic Trouble Code (DTC) informa-
tion to achieve an effective repair.
S
Check bulletins and other service information. This
includes videos, newsletters, etc.
S
Refer to service information (manual) system
check(s).
S
Refer to service diagnostics.
No Trouble Found
This condition exists when the vehicle is found to operate
normally. The condition described by the customer may be
normal. Verify the customer complaint against another ve-
DAEWOO V–121 BL4
ENGINE CONTROLS 1F – 409
hicle that is operating normally. The condition may be in-
termittent. Verify the complaint under the conditions de-
scribed by the customer before releasing the vehicle.
Re–examine the complaint.
When the complaint cannot be successfully found or iso-
lated, a re–evaluation is necessary. The complaint should
be re–verified and could be intermittent as defined in "In-
termittents," or could be normal.
After isolating the cause, the repairs should be made. Vali-
date for proper operation and verify that the symptom has
been corrected. This may involve road testing or other
methods to verify that the complaint has been resolved un-
der the following conditions:
S
Conditions noted by the customer.
S
If a DTC was diagnosed, verify a repair by duplicat-
ing conditions present when the DTC was set as
noted in the Failure Records or Freeze Frame data.
Verifying Vehicle Repair
Verification of the vehicle repair will be more comprehen-
sive for vehicles with On–Board Diagnostic (OBD II) sys-
tem diagnostics. Following a repair, the technician should
perform these steps:
Important : Follow the steps below when you verify re-
pairs on OBD II systems. Failure to follow these steps
could result in unnecessary repairs.
S
Review and record the Failure Records and the
Freeze Frame data for the DTC which has been
diagnosed (Freeze Fame data will only be stored
for an A or B type diagnostic and only if the MIL
has been requested).
S
Clear the DTC(s).
S
Operate the vehicle within conditions noted in the
Failure Records and Freeze Frame data.
S
Monitor the DTC status information for the specific
DTC which has been diagnosed until the diagnostic
test associated with that DTC runs.
OBD II SERVICEABILITY ISSUES
Based on the knowledge gained from On–Board Diagnos-
tic (OBD II) experience in the 1994 and 1995 model years,
this list of non–vehicle faults that could affect the perfor-
mance of the OBD II system has been compiled. These
non–vehicle faults vary from environmental conditions to
the quality of fuel used. With the introduction of OBD II
diagnostics across the entire passenger car and light–duty
truck market in 1996, illumination of the MIL due to a non–
vehicle fault could lead to misdiagnosis of the vehicle, in-
creased warranty expense and customer dissatisfaction.
The following list of non–vehicle faults does not include ev-
ery possible fault and may not apply equally to all product
lines.
Fuel Quality
Fuel quality is not a new issue for the automotive industry,
but its potential for turning on the Malfunction Indicator
Lamp (MIL) with OBD II systems is new.