DSG-423 ENGINE CONTROLS
08-36
Visual Inspection
Perform a careful visual and physical engine inspection
before performing any diagnostic procedure. Perform
all necessary repairs before proceeding with additional
diagnosis, this can often lead to repairing a problem
without performing unnecessary steps. Use the
following guidelines when performing a visual/physical
inspection check:
• Inspect engine for modifications or aftermarket
equipment that can contribute to the symptom; verify
that all electrical and mechanical loads or accessory
equipment is “OFF” or disconnected before
performing diagnosis.
• Inspect engine fluids for correct levels and evidence
of leaks.
• Inspect vacuum hoses for damage, leaks, cracks,
kinks and improper routing, inspect intake manifold
sealing surface for a possible vacuum leak.
• Inspect PCV valve for proper installation and
operation.
• Inspect all wires and harnesses for proper
connections and routing; bent or broken connector
pins; burned, chafed, or pinched wires; and
corrosion. Verify that harness grounds are clean and
tight.
• Inspect GCP, sensors and actuators for physical
damage.
• Inspect GCP grounds for cleanliness, tightness, and
proper location.
• Inspect fuel system for adequate fuel level, and fuel
quality (concerns such as proper octane,
contamination, winter/summer blend).
• Inspect intake air system and air filter for restrictions.
• Inspect battery condition and starter current draw.
If no evidence of a problem is found after visual
inspection has been performed, proceed to “Diagnostic
System Check”
Intermittent Problems
NOTE: An intermittent problem may or may not turn on
the MIL or store a DTC. Do not use the DTC charts for
intermittent problems. The fault must be present to
locate the problem.
NOTE: Most intermittent problems are caused by faulty
electrical connections or wiring. Perform a careful visual
inspection 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 terminals
• Improper contact tension. All connector terminals in
the problem circuit should be carefully checked.
• Poor terminal-to-wire connections. This requires
removing the terminal from the connector body to
check.
• Improperly installed aftermarket equipment or
accessories.
Operate the engine with accessories “OFF” and a
suitable multimeter connected to the suspected circuit.
An abnormal voltage when the malfunction occurs is a
good indication that there is a fault in the circuit being
monitored.
To check GCP for loss of diagnostic code memory,
disconnect the MAP sensor connector and idle the
engine until the MIL illuminates. Perform MIL DTC
retrieval procedure. DTC should be stored and kept in
memory when the ignition is turned “OFF”. If not, the
GCP is faulty. When this test is completed, make sure
that you clear the DTC from memory. An intermittent
MIL with no stored DTC may be caused by the
following:
• Ignition coil shorted to ground and arcing at plugs.
• MIL circuit to GCP shorted to ground.
• Poor GCP grounds.
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