Inspection/Test
| Action
|
DEFINITION: The problem is not currently present but is indicated in DTC History.
OR
There is a customer complaint, but the symptom can not currently be duplicated,
if the problem is not DTC related.
|
Preliminary
| Refer to
Symptoms - Engine Controls
before starting.
|
Harness/Connector
| Many intermittent open or shorted circuits are affected by harness/connector
movement that is 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 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 component 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.
|
Electrical Connections or Wiring
| Poor electrical connections, terminal tension or wiring problems cause most
intermittents. Refer to
Testing for Intermittent Conditions and Poor Connections
,
Circuit Testing
, or
Wiring Repairs
to perform the following inspections:
| • | Inspect for poor mating of the connector halves, or terminals incorrectly
seated in the connector body. |
| • | Inspect for incorrectly 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. 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. |
| • | Ensure that the wiring does not come in contact with hot exhaust components. |
|
Control Module Power and Grounds
Component Power and Grounds
| Poor power or ground connections can cause widely varying symptoms.
| • | Test all control module power supply circuits. Many vehicles have multiple
circuits supplying power to the control module. Other components in the system may
have separate power supply circuits that may also need to be tested. Inspect connections
at the module/component connectors, fuses, and any intermediate connections between
the power source and the module/component. A test lamp or a DMM may indicate that
voltage is present, but neither tests the ability of the circuit to carry sufficient
current. Ensure that the circuit can carry the current necessary to operate the component.
Refer to
Circuit Testing
and
Power Distribution Schematics
. |
| • | Test all control module ground and system ground circuits. The control
module 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
and
Ground Distribution Schematics
. |
|
Temperature Sensitivity
|
| • | An intermittent condition may occur when a component/connection reaches
normal operating temperature. The condition may occur only when the component/connection
is cold, or only when the component/connection is hot. |
| • | Freeze Frame, Failure Records, Snapshot, or Vehicle Data Recorder 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. Test for water intrusion. |
| - | The condition only occurs on a cold start. |
| - | The condition goes away when the vehicle warms up. |
| • | Information from the customer may help to determine if the trouble follows
a pattern that is temperature related. |
|
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, or an
engine control module (ECM) driven solenoid or switch. These conditions can cause
a sharp electrical surge. Normally, the problem will occur when the malfunctioning
component is operating. |
| • | incorrect installation of non-factory or aftermarket add on accessories
such as lights, 2-way radios, amplifiers, electric motors, remote starters, alarm
systems, cell phones, etc. These accessories may lead to an emission related OBD II
failure while in use, but do not fail when the accessories are not in use. Refer to
Checking Aftermarket Accessories
. |
| • | Test for an open diode across the A/C compressor clutch and for other
open diodes. Some relays may contain a clamping diode. |
| • | Test the generator for a bad rectifier bridge that may be allowing AC
noise into the electrical system. Refer to
Symptoms - Engine Electrical
. |
|
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.
|
| • | 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
Control Module References
, for replacement, setup, and programming. |
|
Duplicating Failure Conditions
|
| • | If none of the previous tests 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. |
| 1. | Review and record Freeze Frame/Failure Records data |
| 2. | Clear the DTCs using the scan tool. |
| 3. | Turn the key to OFF and wait 15 seconds. |
| 4. | 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. |
| 5. | 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 the 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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