Checks
| Action
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Definition:
The problem is not currently present but is indicated in DTC History.
OR
There is a customer complaint, 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. |
|
Harness/Connector
Check
| Many
intermittent open or shorted circuits come and go with harness/connector movement
caused by vibration, engine torque, bumps/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 component's 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/system
operation, or the engine operation, inspect and repair the harness/connections
as necessary. Refer to Electrical Connections or Wiring in this table.
|
Electrical Connections or Wiring
| Faulty 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 faulty terminal to wire connections including terminals
crimped over insulation. This requires removing the terminal from the connector
body. |
| • | Inspect for corrosion and 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
Symptoms
.
|
ECM Power and Grounds
| Faulty power or ground connections can cause widely varying symptoms.
| • | Test all 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. A
test lamp or a DMM may indicate that voltage is present, but neither tests
a circuit's ability to carry sufficient current. Ensure that the circuit
can carry the current necessary to operate the component. Refer to
Engine Controls Schematics
. |
| • | 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. Inspect grounds for clean and tight
connections 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. |
|
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 faulty 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).
|
Electromagnetic Interference (EMI) and Electrical Noise.
| Some electrical components/circuits
are sensitive to EMI or other types of electrical noise. Inspect for the following
conditions:
| • | A misrouted harness that is too close to high voltage/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, etc. |
| • | Test for an open diode across the A/C compressor clutch and
for other open diodes. |
| • | Test the generator for a faulty rectifier bridge that may be allowing
AC noise into the electrical system. |
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Duplicating
Failure Conditions
| If none of the previous checks are 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 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.
|
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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