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 DTC(s) 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 Cooling and Radiator
for diagnosis. |
| • | Scan tool data is within normal operating range, Refer to Typical Scan Data Values
. |
| - | An example of incorrect scan data would be an indication of the
extended travel brake switch always applied. With this condition the PCM may
operate the engine in a torque reduction mode at higher throttle angles. The
torque reduction mode may cause a driveability concern. This condition may
not set a DTC. |
| • | 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 check 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. |
| • | 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. This requires removing the
terminal from the connector body to check. |
Road test the vehicle with a J 39200 Digital Multimeter 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 a 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. |
| • | Poor PCM grounds, refer to PCM wiring diagrams. |
Check 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 .Check all wires from the PCM to the ignition
control module for poor connections.
Check for open diode across A/C compressor clutch and check for other
open diodes, refer to wiring diagrams in ELECTRICAL DIAGNOSIS.
The following Symptom tables are located in this section:
| • | Lack of Power, Sluggishness, or Sponginess |
| • | Rough, Unstable, or Incorrect Idle and Stalling |
| • | Excessive Exhaust Emissions or Odors |
| • | Hesitation, Sag, Stumble |
| • | Restricted Exhaust System Check |
