Important Preliminary Checks Before Starting
Before using this section, perform the Powertrain On-Board Diagnostic
(OBD) System Check and verify all of the following conditions:
| • | The ECM and the malfunction indicator lamp (MIL) are operating
correctly. |
| • | There are no DTCs stored. |
| • | Verify the customer complaint. Then, locate the correct symptom
in the table of contents. Perform the procedure which is included in the symptom
table. |
Visual/Physical Check
Several of the symptom procedures call for a careful visual/physical
inspection. This inspection can lead to correcting a problem without further
checks and can save valuable time. This check should include the following
items:
| • | The ECM grounds for being clean, tight, and in the proper location. |
| • | The vacuum hoses for any splits or any kinks, and proper connections,
as shown on the Vehicle Emission Control Information label. Check thoroughly
for any type of leak or restriction. |
| • | The air intake ducts for collapsed or damaged areas |
| • | Air leaks at the throttle body mounting area, the mass air flow
(MAF) sensor, the duct work between the MAF and the throttle body, and the
intake manifold sealing surfaces. |
Intermittents
Important: 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 any
intermittent problems. The fault must be present in order to locate the problem.
Most intermittent problems are caused by poor 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) |
| • | An improperly formed or damaged terminal |
| • | All connector terminals in the problem circuit should be carefully
checked for proper contact tension. Refer to
Wiring Repairs
in Wiring Systems for the proper procedure. |
| • | A poor terminal to wire connection--This requires removing
the terminal from the connector body in order to check. Also, check for the
terminal being crimped over the insulation. |
Road test the vehicle with a J 39200
DMM connected to a suspected circuit. An abnormal voltage when
a malfunction occurs is a good indication that there is a fault in the circuit
being monitored.
The Tech 2 scan tool has several features that are useful for locating
intermittent conditions. Use the following features in order to find the
intermittent faults:
| • | The Snapshot feature can be triggered to capture and store the
engine parameters within the scan tool when the malfunction occurs. You can
review this stored information in order to determine what caused the malfunction,
or what conditions were present when the problem occurred. |
| • | Reviewing the Freeze Frame data can also aid in locating an intermittent
condition. Review and record the information in the Freeze Frame that is associated
with the intermittent DTC being diagnosed. The vehicle can be driven within
the conditions that were present when the DTC originally set. |
An intermittent MIL with no stored DTC may be caused by poor ECM grounds.
Refer to the ECM wiring diagrams.
If the intermittent condition exists as a start and then a stall, check
for DTCs relating to the vehicle theft deterrent system.
Check for improper installation of electrical options such as lights,
cellular phones etc.
Check for an open diode across the A/C compressor clutch. Then, check
for other open diodes. Refer to
Wiring Repairs
in Wiring Systems.
