Inspections
| Action
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DEFINITION: The condition is not currently present but is indicated in DTC history.
OR
There is a customer concern, but the symptom cannot currently be duplicated,
if the condition is not DTC related.
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Preliminary
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| • | The fault must be present to locate a problem using the DTC table. If
a fault is intermittent, the use of DTC tables may result in the replacement of
good parts. |
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Visual/Physical
| This step is an important aid for locating a condition without extensive testing.
Perform a thorough visual and physical inspection of the following:
| • | Wiring harness for damage or cuts |
| • | A misrouted harness that is too close to high voltage or high current
devices such as the following: |
| - | Secondary ignition components |
| • | Vacuum hoses for the following conditions: |
| - | Splits in the hose or the connections |
| • | Air leaks at the throttle body mounting area |
| • | Engine control module (ECM) and body grounds are clean and tight |
| • | Battery connections are clean and tight |
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Harness/Connector Test
| Many intermittent open or shorted circuits may be affected with harness and
connector movement caused by vibration, engine torque, bumps and rough pavement,
etc. Test for this type of condition by performing the applicable procedure from
the following list:
| • | Move the related connectors and wiring while monitoring the appropriate
scan tool data. |
| • | Move the related connectors and wiring with the component commanded ON
and OFF, with the scan tool. Observe the operation of the component. |
| • | With the engine running, move the related connectors and wiring while
monitoring engine operation. |
If harness or connector movement affects the data displayed, the component,
system operation, or the engine operation inspect and repair the harness or connections
as necessary. Refer to Electrical Connections or Wiring in this table.
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Electrical Connections or Wiring
| Poor electrical connections and terminal tension or wiring faults cause most
intermittents. Perform a careful inspection of the suspected circuit for the
following:
| • | Incorrect mating of the connector halves, or terminals not fully seated
in the connector body |
| • | Improperly formed or damaged terminals |
| • | Incorrect terminal tension |
| • | Poor terminal to wire connections including terminals crimped over insulation.
This requires removing the terminal from the connector body |
| • | Corrosion or water intrusion. Pierced or damaged insulation can allow
moisture to enter the wiring. The conductor can corrode inside the insulation with
little visible evidence. Look for swollen and stiff sections of wire in the suspect
circuits |
| • | Wires that are broken inside the insulation |
| • | Pinched, cut, or rubbed through wiring |
| • | The wiring coming in contact with hot exhaust components |
Refer to
Testing for Intermittent Conditions and Poor Connections
, and
Connector Repairs
in Wiring
Systems.
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ECM Power and Grounds
| Poor power or ground connections can cause widely varying symptoms.
| • | Test all engine control module (ECM) power circuits. Many vehicles have
multiple circuits supplying power to the ECM. Inspect connections at the ECM connectors,
fuses, and any intermediate connections between the power source and the ECM or
component. A test lamp or a DMM may indicate that voltage is present, but neither
tests the ability of a circuit to carry sufficient current. Ensure that the circuit
can carry the current necessary to operate the component. Refer to
Power Distribution Schematics
in Wiring Systems. |
| • | Test all ECM ground and system ground circuits. The ECM may have multiple
ground circuits. Other components in the system may have separate grounds that
may also need to be tested. Ensure the ground connections are clean and tight at
the grounding point. Inspect the connections at the component and in splice packs,
where applicable. Ensure that the circuit can carry the current necessary to operate
the component. Refer to
Ground Distribution Schematics
in Wiring Systems. |
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Temperature Sensitivity
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| • | An intermittent condition may occur only when the component is cold,
or only when the component is hot. The heat that affects the circuit can be generated
by the engine, a poor connection, or a high electrical load. |
| • | Information from the customer may help to determine if the trouble follows
a pattern that is temperature related. The Freeze Frame/Failure Records or Snapshot
data may help with this type of intermittent condition, where applicable. |
| • | If the intermittent condition is related to heat, review the captured
data for a relationship with the following: |
| - | High ambient temperatures |
| - | Underhood/engine generated heat |
| - | Circuit generated heat due to a poor connection, or high electrical load |
| - | Higher than normal load conditions (towing, etc.) |
| • | If the intermittent is related to cold, review the captured data for a
relationship with the following: |
| - | Low ambient temperatures--In extremely low temperatures, ice may
form in a connection or component. Inspect for water intrusion. |
| - | The condition only occurs on a cold start. |
| - | The condition goes away when the vehicle warms up. |
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Electromagnetic Interference (EMI) and Electrical Noise.
| Some electrical components and circuits are sensitive to electromagnetic interference
(EMI) or other types of electrical noise. Inspect for the following conditions:
| • | A misrouted harness that is too close to high voltage and high current
devices such as secondary ignition components, motors, generator, etc. These components
may induce electrical noise on a circuit that could interfere with normal circuit
operation. |
| • | Electrical system interference caused by a malfunctioning relay, ECM
driven solenoid, or switch. They can cause a sharp electrical surge. Normally,
the problem will occur when the malfunctioning component is operating. |
| • | Incorrect installation of aftermarket accessories such as lights, 2-way
radios, amplifiers, electric motors, remote starters, alarm systems, cell phones,
etc. |
| • | An open diode across the A/C compressor clutch and for other open diodes--Some
relays may contain a clamping diode or resistor. |
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Incorrect ECM Programming
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| • | There are only a few situations where reprogramming an ECM is appropriate: |
| - | An ECM from another vehicle is installed. |
| - | Revised software/calibration files have been released for this vehicle. |
| | Important: DO NOT reprogram the ECM with the SAME software/calibration files that are
already present in the ECM. This is not an effective repair for any type of driveability
problem.
|
| • | Verify that the ECM contains the correct software/calibration. If incorrect
programming is found, reprogram the ECM with the most current software/calibration.
Refer to
Service Programming System (SPS)
in Programming. |
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Duplicating Failure Conditions
| If the previous tests were not successful, attempt to duplicate and/or capture
the failure conditions.
Freeze Frame/Failure Records data, where applicable, contains the conditions
that were present when the DTC set.
- Review and record the Freeze Frame/Failure Records data.
- Clear any DTCs with a scan tool.
- Turn OFF the key and wait 15 seconds.
- Operate the vehicle under the same conditions that were noted in Freeze
Frame/Failure Records. The vehicle must also be operating within the Conditions
For Running the DTC. Refer to Conditions for Running the DTC in the supporting
text of the DTC being diagnosed.
- Monitor DTC status for the DTC being tested. The scan tool will indicate
Ran when the enabling conditions have been satisfied long enough for the DTC to
run. The scan tool will also indicate whether the DTC passed or failed.
An alternate method is to drive the vehicle with a DMM connected to a suspected
circuit. An abnormal reading on the DMM when the problem occurs may help you locate
the problem.
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Scan Tool Snapshot
| The scan tool can be set up to take a snapshot of the parameters available
via serial data. The Snapshot function records live data over a period of time.
The recorded data can be played back and analyzed. The scan tool can also graph
parameters singly or in combinations of parameters for comparison. The snapshot
can be triggered manually at the time the symptom is noticed or set up in advance
to trigger when a DTC sets.
An abnormal value captured in the recorded data may point to a system or component
that needs to be investigated further.
Refer to the scan tool user instructions for more information on the Snapshot
function.
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