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
true:
| • | The malfunction indicator lamp (MIL) is OK |
Verify the customer complaint 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 call for a careful visual/physical
check. The importance of this step cannot be stressed too strongly. The visual/physical
check can lead to correcting a problem without further diagnostics and save
valuable time. This inspection should include the following concerns:
| • | The PCM grounds are clean and tight and in the correct locations. |
| • | The vacuum hoses are OK and connected correctly as shown on Vehicle
Emission Control Information label. |
| • | There are no vacuum leaks at the throttle body mounting and the
intake manifold sealing surfaces. |
| • | The wiring is OK and correctly positioned. |
Intermittents
Important: A problem may or may not turn on the MIL or store a DTC. DO NOT use
the DTC tables for intermittent problems. The fault must be present in
order to locate the problem.
Most intermittent problems are caused by faulty electrical connections
or wiring. Perform careful visual/physical inspections and tests for the following
conditions:
| • | An incorrect mating of the connector halves or a terminal not
fully seated in the connector (backed out). |
| • | An incorrectly formed terminal or a damaged terminal. |
| • | All of the connector terminals in the faulty circuit should be
carefully tested for the correct contact tension. |
| • | A faulty terminal to wire connection. This may require removing
the terminal from the connector body in order to inspect the connection. |
The vehicle may need to be driven with a DMM connected to the 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 test for loss of DTC memory, disconnect the throttle position (TP)
sensor and idle the engine until the MIL illuminates. DTC P0122 should
be stored and kept in memory when the ignition is turned off. If the DTC
is not stored, the PCM is faulty. When this test is complete, make sure
that you clear the DTC P0122 from memory.
An intermittent MIL with no stored DTC may be caused by the following
concerns:
| • | An ignition coil shorted to ground and arcing at the ignition
wires or at the spark plugs. |
| • | An MIL wire to the PCM shorted to ground. |
If the intermittent condition exists as a start and stall, inspect for
DTCs relating to the vehicle theft deterrent system.
Test for an electrical system interference caused by the following components:
The above components can cause a sharp electrical surge. Normally,
the problem will occur when the malfunctioning component is operated.
Inspect for improper installation of electrical options such as lights,
cellular phones, etc.
All of the ignition control module (ICM) wiring should be routed away
from the generator. Inspect all of the wires from the PCM to the ICM for faulty
connections.
Test for an open diode across the A/C compressor clutch, or other open
diodes.
