Checks
| Action
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DEFINITION:
The problem 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 problem is not DTC related.
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Preliminary Inspection
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| • | Refer to Important Preliminary Inspection Before Starting in
Symptoms
. |
| • | 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 Inspection
| This step is an important
aid for locating a condition without extensive testing. Perform a thorough
visual and physical inspection of the following items:
| • | 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: |
| - | Splits in the hose or the connections |
| • | Air leaks at the throttle body mounting area, the mass air flow
(MAF) sensor, and at the intake manifold |
| • | The MAF sensor installation |
| • | ECM and body grounds are being clean and tight |
| • | Battery connections are clean and tight |
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Harness/Connector Check
| Many intermittent open or shorted circuits come and go
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 components operation. |
| • | 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
and 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:
| • | Inspect for incorrect mating of the connector halves, or terminals
not fully seated in the connector body, backed-out. |
| • | Inspect for improperly formed or damaged terminals. Test for incorrect
terminal tension. |
| • | Inspect for poor terminal to wire connections including terminals
crimped over insulation. This requires removing the terminal from the connector
body. |
| • | Inspect for 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. |
| • | Inspect for wires that are broken inside the insulation. |
| • | Inspect the harness for pinched, cut, or rubbed through wiring. |
| • | Make sure the wiring does not come in contact with hot exhaust
components. |
Refer to
Testing for Intermittent Conditions and Poor Connections
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 a circuits ability
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. Make sure 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. |
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Temperature Sensitivity
|
| • | 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 engine generated or due to a poor connection in the circuit
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 is related to heat, review the 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 data for the
following: |
| - | Low ambient temperatures -- In extremely low temperatures,
ice may form in a connection or component. Check 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 non-factory, aftermarket, add-on accessories
such as lights, 2-way radios, amplifiers, electric motors, remote starters,
alarm systems, cell phones, etc. |
| • | Test for 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
|
| • | There are only a few situations where reprogramming an ECM is
appropriate: |
| - | A new service ECM is installed. |
| - | An ECM from another vehicle is installed. |
| - | Revised software/calibration files have been released for this
vehicle. |
| | Important:: DO NOT re-program 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.
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Duplicating Failure Conditions
| If the previous checks were not successful,
attempt to duplicate and/or capture the failure conditions.
Freeze Frame and Failure Records data, where applicable, contains the
conditions that were present when the DTC set.
- Review and record the Freeze Frame and Failure Records data.
- Clear any DTCs using the scan tool.
- Turn the key to OFF and wait 15 seconds.
- Operate the vehicle under the same conditions that were noted
in Freeze Frame and Failure Records data, as closely as possible. 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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