Important Preliminary Checks Before Starting
Before using this section, perform the Powertrain On-Board Diagnostic
(OBD) System Check and verify all of the following items:
| • | The PCM and MIL (Service Engine Soon) are operating correctly. |
| • | There are no DTCs stored. |
| • | Ensure that the engine coolant temperature is not above 130°C
(266°F). This condition will cause the PCM to operate in Engine Metal
Overtemp. While in Engine Metal Overtemp, the PCM will turn fuel off to
four cylinders at a time to keep engine temperatures from reaching damaging
levels. Engine Metal Overtemp will be perceived as a lack of power, miss,
or rough idle. If the vehicle is operating in Engine Metal Overtemp, refer
to Engine Overheating in Engine Cooling for diagnosis. |
| • | Verify the customer complaint and locate the correct symptom
in the table of contents. Perform the procedure included in the symptom chart. |
Visual/Physical Check
Several of the symptom procedures call for a careful Visual/Physical.
It can lead to correcting a problem without further checks and can save valuable
time. This inspection should include the following items:
| • | PCM grounds for being clean, tight, and in their proper location |
| • | Vacuum hoses for splits, kinks, and proper connections, as shown
on Vehicle Emission Control Information label. Check thoroughly for any type
of leak or restriction |
| • | Air intake ducts for collapsed or damaged areas |
| • | Air leaks at throttle body mounting area, mass air flow (MAF)
sensor and intake manifold sealing surfaces |
| • | Inspect for a tight or binding cruise control cable. |
| • | Ignition wires for cracking, hardness, proper routing and carbon
tracking. |
| • | Wiring for proper connections, pinches and cuts. |
Intermittents
A problem may or may not turn ON the malfunction indicator lamp (MIL)
or store a DTC. DO NOT use the Diagnostic Trouble Code (DTC) charts for intermittent
problems. The fault must be present to locate the problem.
Most intermittent problems are caused by faulty electrical connections
or wiring. Perform a careful visual/physical check for the following conditions:
| • | Poor mating of the connector halves or a terminal not fully seated
in the connector (backed out) |
| • | Improperly formed or damaged terminal |
| • | All connector terminals in the problem circuit should be carefully
checked for proper contact tension |
| • | Poor terminal to wire connection |
| | To properly inspect connection, remove the terminal from the connector
body. |
Road test the vehicle with the DMM connected to a suspected circuit.
An abnormal voltage when malfunction occurs is a good indication that there
is a fault in the circuit being monitored.
Use the scan tool to help detect intermittent conditions. The scan
tool has several features that can be used to locate an intermittent condition.
Use the following features to find intermittent faults:
| • | The Snapshot feature can be triggered to capture and store engine
parameters within the scan tool when the malfunction occurs. This stored information
then can be reviewed by the service technician to see what caused the malfunction. |
| • | Using a Scan Tools Freeze Frame data or Failure Records data
can also aid in locating an intermittent condition. Review and record the
information in the freeze frame or failure record associated with the intermittent
DTC being diagnosed. The vehicle can be driven within the conditions that
were present when the DTC originally set |
Loss of diagnostic code memory. To check, disconnect the MAP sensor
and idle engine until the MIL (Service Engine Soon) comes ON. DTC P0107
should be stored and kept in memory when ignition is turned OFF. If not
the PCM is faulty. When this test is completed, make sure that you clear
the DTC P0107 from memory.
An intermittent MIL (Service Engine Soon) with no stored DTC may be
caused by the following:
| • | Ignition coil shorted to ground and arcing at ignition wires
or plugs |
| • | MIL (Service Engine Soon) wire to PCM shorted to ground |
Inspect for improper installation of electrical options such as lights,
cellular phones etc. Route ignition control (IC) Module wiring away from secondary
ignition wires and ignition coils. Inspect all wires from the PCM to the
ignition control module for poor connections.
Inspect for open diode across A/C compressor clutch and inspect for
other open diodes
The following Symptom tables are located in this section:
