6E1-44 DRIVEABILITY AND EMISSIONS
VERIFYING VEHICLE REPAIR
Verification of the vehicle repair will be more
comprehensive for vehicles with OBD system
diagnostics. Following a repair, the technician should
perform the following steps:
Important: Follow the steps below when you verify
repairs on OBD systems. Failure to follow these steps
could result in unnecessary repairs.
1. Review and record the customer complaint for the
DTC which has been diagnosed.
2. Clear the DTC(s).
3. Operate the vehicle within conditions noted in the
customer complaint.
4. Monitor the DTC status information for the specific
DTC which has been diagnosed until the diagnostic
test associated with that DTC runs.
GENERAL SERVICE
INFORMATION
OBD SERVICEABILITY ISSUES
Fuel Quality
Fuel quality is not a new issue for the automotive
industry. The Reed Vapor Pressure of the fuel can
also create problems in the fuel system, especially
during the spring and fall months when severe
ambient temperature swings occur. A high Reed
Vapor Pressure could show up as a rich DTC due to
excessive canister loading. High vapor pressures
generated in the fuel tank can also affect the
Evaporative Emission diagnostic as well.
Using fuel with the wrong octane rating for your
vehicle may cause driveability problems. Many of the
major fuel companies advertise that using “premium”
gasoline will improve the performance of your vehicle.
Most premium fuels use alcohol to increase the
octane rating of the fuel. Although alcohol-enhanced
fuels may raise the octane rating, the fuel's ability to
turn into vapor in cold temperatures deteriorates. This
may affect the starting ability and cold driveability of
the engine.
Low fuel levels can lead to fuel starvation, lean engine
operation, and eventually engine misfire.
Non-OEM Parts
All of the OBD diagnostics have been calibrated to run
with OEM parts. Small leaks in the exhaust system
near the heated oxygen sensor can also cause the
MIL (“Check Engine“ lamp) to turn on.
Aftermarket electronics, such as cellular phones,
stereos, and anti-theft devices, may radiate EMI into
the control system if they are improperly installed. This
may cause a false sensor reading and turn on the MIL
(“Check Engine” lamp).
Poor Vehicle Maintenance
The sensitivity of OBD diagnostics will cause the MIL
(“Check Engine” lamp) to turn ON if the vehicle is not
maintained properly. Restricted air filters, fuel filters,
and crankcase deposits due to lack of oil changes or
improper oil viscosity can trigger actual vehicle faults.
Poor vehicle maintenance can not be classified as a
“non-vehicle fault” , but with the sensitivity of OBD
diagnostics, vehicle maintenance schedules must be
more closely followed.
Related System Faults
Many of the OBD system diagnostics will not run if the
ECM detects a fault on a related system or
component. One example would be that if the ECM
detected a Evap. Purge Solenoid fault, The diagnosis
on the Oxygen Sensor (If applicable) would be
suspended until the Evap. Purge Solenoid repaired. If
this happened, the customer may have to make two
trips to the dealership in order to repair the vehicle.
MAINTENANCE SCHEDULE
Refer to the Maintenance Schedule.
VISUAL/PHYSICAL ENGINE
COMPARTMENT INSPECTION
Perform a careful visual and physical engine
compartment inspection when performing any
diagnostic procedure or diagnosing the cause of an
emission test failure. This can often lead to repairing a
problem without further steps. Use the following
guidelines when performing a visual/thysical
inspection:
• Inspect all vacuum hoses for punches, cuts,
disconnects, and correct routing.
• Inspect hoses that are difficult to see behind other
components.
• Inspect all wires in the engine compartment for
proper connections, burned or chafed spots,
pinched wires, contact with sharp edges or contact
with hot exhaust manifolds or pipes.
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