Important Preliminary Checks Before Starting
Perform
Powertrain On Board Diagnostic (OBD) System Check
before using the Symptom Tables, and
verify all of the following are true:
| • | The PCM and MIL (Service Engine Soon) are operating correctly. |
| • | There are no DTCs stored. |
| • | Ensure that the engine coolant temperature is not above 132°C
(270°F). This condition causes the PCM to operate in Engine
Coolant Over temperature-Fuel Disabled Mode. While in Engine
Coolant Over temperature-Fuel Disabled Mode, the PCM turns
fuel off to four cylinders at a time to keep engine temperatures
from reaching damaging levels. The customer perceives Engine
Coolant Over temperature-Fuel Disabled Mode as a lack of power,
miss, or rough idle. If the engine operates in Engine Coolant
Over temperature-Fuel Disabled Mode, refer to
Engine Overheating
in Engine Cooling. |
| • | Verify the customers concern, and locate the correct symptom in
the table of contents. Inspect the items indicated under that symptom. |
Visual/Physical Check
Several of the symptom procedures ask for a thorough Visual/Physical
inspection. This step is extremely important - it can lead to correcting
a condition without further inspections and can save valuable
time. This inspection includes:
| • | Vacuum hoses for splits, kinks, and proper connections, as shown
on the Vehicle Emission Control Information label. Inspect thoroughly for
any type of leak or restriction. |
| • | The Mass Air Flow (MAF) sensor installation. The arrows on the
plastic portion of the sensor must point toward the engine. |
| • | The air intake ducts for being collapsed or for having damaged
areas. |
| • | Air leaks at throttle body mounting area, Mass Air Flow (MAF)
sensor, and the intake manifold sealing surfaces. |
| • | The ignition wires for cracking, hardness, proper routing and
carbon tracking. |
| • | The engine wiring harness and terminals for proper connections,
pinches or cuts. |
Intermittent
Important: Inspect for improper installation of electrical components if an intermittent
condition exists. Inspect for aftermarket theft deterrent devices, lights
and cellular phones. Ensure that no aftermarket equipment is connected
to the Class 2 circuit. If you can not locate an intermittent
condition, a cellular phone signal communication may cause the
condition.
Important: The condition may or may not turn ON the Malfunction Indicator Lamp
(MIL) or store a DTC. DO NOT use the Diagnostic Trouble Code (DTC) tables
for intermittent conditions. The fault must be present in order to locate
the condition.
Faulty electrical connections or wiring cause most intermittent conditions.
Perform a thorough visual/physical inspection for the following conditions:
| • | Poor mating of the connector halves or a terminal not fully seated
in the connector body (backed out). Refer to
Repairing Connector Terminals
in Wiring Systems. |
| • | Reform or replace connector terminals in the circuit in order
to insure proper contact tension. Refer to
Repairing Connector Terminals
in Wiring Systems. |
| • | Poor terminal to wire connection requires removing the terminal
from the connector body in order to inspect. Refer to
Connector Repairs
in Wiring Systems. |
Road test the vehicle with a Digital Multimeter (DMM) J 39200
connected to the suspected circuit.
An abnormal voltage when the malfunction occurs is a good indication that
there is a malfunction in the circuit being monitored.
Use a scan tool in order to help detect intermittent conditions. The
GM Techline equipment (Scan Tool) has several features that you can use to
locate an intermittent condition. Use the following features to
find intermittent faults:
| • | You can trigger the Snapshot feature in order to capture and store
engine parameters within the scan tool when the malfunction occurs. You can
then review this stored information in order to see what caused
the malfunction. |
| • | Using the Scan Tool Freeze Frame or Failure Records option can
also aid in locating an intermittent condition. Review and capture the
information in the Freeze Frame and/or Failure record associated
with the intermittent DTC being diagnosed. Drive the vehicle in
the conditions that were present when the DTC originally set. |
Important: If the intermittent condition exists as a start and stall, search for
DTCs related to the vehicle theft deterrent system. Inspect for improper
installation of electrical options such as lights, cellular phones
etc.
Any of the following may cause an intermittent Malfunction Indicator
Lamp (MIL) with no stored DTC:
| • | The ignition coils shorted to a ground, arcing at the ignition
wires or the spark plugs. |
| • | The Ignition Control (IC) wires for being routed to close to the
secondary ignition wires, coils, or the generator. Ensure that all
of the circuits from the PCM to the ignition coils have good connections. |
| • | An open diode across the A/C compressor clutch and other open
diodes. |
Use the following tables when diagnosing a symptom complaint:
