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 Checks
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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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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. Check for this type of condition by performing
the applicable procedure from the following list:
| • | Move related connectors and wiring while monitoring the appropriate
scan tool data. |
| • | Move related connectors and wiring with the component commanded
ON and OFF with the scan tool. Observe the components operation. |
| • | With the engine running, move related connectors and wiring while
monitoring engine operation. |
If harness or connector movement affects the data displayed, component/system
operation, or engine operation inspect and repair the harness/connections
as necessary. Refer to Electrical Connections or Wiring
in this table.
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Electrical Connections or Wiring
| Poor electrical
connections/terminal tension or wiring problems cause most intermittents.
Perform a careful inspection of the suspected circuit for the
following:
| • | Inspect for poor 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 poor
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/water intrusion. |
| • | Inspect the harness for pinched, cut or rubbed through wiring. |
| • | Make sure 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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PCM Power and Grounds
| Poor power
or ground connections can cause widely varying symptoms.
| • | Test all powertrain control module (PCM) power circuits. Many
vehicles have multiple power circuits feeding the PCM. Inspect connections
at the PCM connectors, fuses, and any intermediate connections
between the power source and the PCM. 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
Circuit Testing
in Wiring
Systems. |
| • | Test all PCM ground and system ground circuits. The PCM 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. Refer to
Circuit Testing
in Wiring Systems. |
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Electromagnetic
Interference (EMI) and Electrical Noise
| Some electrical components/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/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,
PCM driven solenoid, or switch--these conditions cause a sharp
electrical surge. Normally, the problem will occur when the
malfunctioning component is operating. |
| • | Improper 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. |
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Incorrect
PCM Programming
| There are only a few situations where reprogramming a PCM is appropriate:
| • | A new service PCM is installed. |
| • | A PCM from another vehicle is installed. |
| • | Revised software/calibration files have been released for this
vehicle. |
Important: DO NOT re-program the PCM with the SAME software/calibration files that
are already present in the PCM. This is not an effective repair for
any type of driveability problem.
Verify that the PCM contains the correct software/calibration information.
If incorrect programming is found, re-program the PCM with the most
current software/calibration information. Refer to
Powertrain Control Module Programming
.
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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 Freeze Frame/Failure Records data.
- Clear 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/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 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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