Important Preliminary Checks
Before Starting
Before using this section you should have performed the Powertrain On
Board Diagnostic (OBD) System Check and determined that the following items
are OK:
| • | The PCM and MIL, check engine, are operating correctly. |
| • | There are no DTCs stored. |
Verify the customer complaint, and locate the correct symptom in the
table of contents. Check the items indicated under that symptom.
Visual/Physical Check
Several of the symptom procedures call for a careful Visual/Physical
Check. The importance of this step cannot be stressed too strongly it can
lead to correcting a problem without further checks and can save valuable
time. This check should include:
| • | PCM grounds for the following conditions: |
| • | Vacuum hoses for the following conditions: |
| - | Proper connections as shown on Vehicle Emission Control Information
label |
| • | Air leaks at the following components: |
| - | Intake manifold sealing surfaces |
| • | Wiring for the following conditions: |
Intermittents
Important: Problem 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
problems. The fault must be present to locate the problem.
Most intermittent problems are caused by faulty electrical connections
or wiring. Perform careful visual/physical check. Check for the following
conditions:
| • | Poor mating of the electrical connector halves or a terminal not
fully seated in the electrical connector (backed out). |
| • | Improperly formed or damaged terminal. |
| • | All electrical 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. |
The vehicle may be driven with a DMM connected to a suspected circuit.
An abnormal voltage is a good indication that there is a malfunction
in the circuit being monitored.
A scan tool can be used to help detect intermittent conditions. The
scan tool has several features that can be used to locate an intermittent
condition.
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 tool's Freeze Frame buffer can also aid in locating an
intermittent condition. Review and record the information in the Freeze Frame
associated with the intermittent DTC being diagnosed. The vehicle can
be driven within the conditions that were present when the DTC originally
set.
To check loss of DTC memory, disconnect TP sensor and idle engine until
the MIL, check engine, comes ON. DTC P0122 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 P0122
from memory.
An intermittent MIL, check engine, with no stored DTC may be caused
by the following:
| • | Ignition coil shorted to ground and arcing at ignition wires or
plugs. |
| • | MIL, check engine, wire to PCM shorted to ground. |
If the intermittent condition exists as a start and then stall, check
for DTCs relating to the vehicle theft deterrent system.
Check for an electrical system interference caused by the following
components:
They can cause a sharp electrical surge. Normally, the problem will
occur when the malfunctioning component is operated.
Check for improper installation of electrical options such as lights,
cellular phones etc.
All Ignition Control Module (ICM) wiring should kept away from the generator.
Check all wires from the PCM to the ignition control module for poor electrical
connections.
Check for an open diode across the A/C compressor clutch and check for
other open diodes.
