Important Preliminary Checks Before Starting
Perform the
Powertrain On Board Diagnostic (OBD) System Check
before using the symptom tables, and
verify that all of the following conditions are true:
| • | The powertrain control module (PCM) and the malfunction indicator
lamp (MIL) are operating correctly. |
| • | There are no DTCs stored. |
| • | 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 the fuel off to 4 cylinders at a time in order
to keep the engine temperatures from reaching damaging levels. The
system perceives Engine Coolant Over Temperature as a lack of power,
a miss, or a rough idle. If the vehicle is operating in Engine Coolant
Over Temperature/Fuel Disabled Mode, diagnosis the system. |
| • | Verify the customer concern and locate the correct symptom in
the table of contents. Inspect the items indicated under that symptom. |
| • | Several of the symptom procedures ask for a Careful Visual/Physical
Check. This step is extremely important, and can lead to correcting a problem
without further checks and can save valuable time. |
| • | If the intermittent condition exists as a start and then a stall,
inspect for any DTCs relating to the theft deterrent system. Verify the proper
installation of electrical options such as lights, cellular phones,
etc. |
Visual/Physical Check
Several of the symptom procedures ask for a Careful Visual/Physical
Check. This step is extremely important, and can lead to correcting a problem
without further checks and can save valuable time. This check includes
the inspection of the following circuits and components:
| • | The PCM grounds for being clean, tight, and in their proper location |
| • | The engine dress cover ground strap |
| • | The vacuum hoses for splits, kinks, and proper connections, as
shown on the Vehicle Emission Control Information label -- Check 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 the throttle body mounting area, the MAF sensor,
and the intake manifold sealing surfaces |
| • | The ignition wires for cracking, for hardness, for proper routing
and for carbon tracking |
| • | The engine harness wiring and terminals for proper connections,
pinches, or cuts |
Intermittent
Important: Check for improper installation of electrical components if an intermittent
condition exists. Inspect for aftermarket theft deterrent devices, for lights,
and for cellular phones. Ensure that no aftermarket equipment is connected
to the Class 2 circuit. If you cannot locate an intermittent condition,
a cellular phone signal communication may cause the condition.
Important: The problem may or may not turn ON the MIL or store a DTC. DO NOT use
the diagnostic trouble code (DTC) tables for intermittent problems. The
fault must be present in order to locate the problem.
Poor electrical connections or improper wiring cause most intermittent
problems. Perform a thorough visual and physical check for the following conditions:
| • | An improperly formed or damaged terminal -- Refer to
Connector Repairs
in Wiring Systems. |
| • | Reform or replace the connector terminals in the problem circuit
in order to insure the proper contact tension. Refer to
Connector Repairs
in Wiring Systems. |
| • | Poor terminal to wire connection requires removing the terminal
from the connector body in order to check. |
Road test the vehicle with a DMM 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
scan tool has several features that you can use in order 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. |
| • | A scan tool Freeze Frame buffer or Failure Records buffer can
also aid in locating an intermittent condition. Review and capture the information
in the Freeze Frame and/or Failure Record that is 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 then a stall, check
for any DTCs relating to the theft deterrent system. Check for improper installation
of electrical options such as lights, cellular phones etc.
Any of the following may cause an intermittent MIL with no stored DTC:
| • | The ignition coils shorted to ground, arcing at the ignition wires
or the spark plugs |
| • | The PCM grounds -- Refer to PCM wiring diagrams. |
| • | The ignition control (IC) wires routed too 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 concern:
- If the condition cannot be isolated using the appropriate table,
refer to
Intermittent Conditions
for
further diagnosis.
