Inspections
| Action
|
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.
|
Preliminary
|
| • | The fault must be present to locate a condition using the DTC table.
If a condition is intermittent, the use of DTC tables may result in the replacement
of good parts. |
| • | Inspect the engine control system grounds for being clean, tight, and
in the correct locations. Refer to
Power and Grounding Component Views
in Wiring Systems and
Engine Controls Schematics
. Ensure the resistance between the engine control
module (ECM) housing and the battery negative cable is less than 0.5 ohms. |
|
Visual/Physical
| This step is an important aid for locating a condition without extensive testing.
Perform a thorough inspection of the following items:
| • | Inspect the wiring harness for damage. |
| • | Inspect for a mis-routed harness that is too close to high voltage or
high current devices such as the following: |
| - | Secondary ignition components |
| - | Motors and generators. These components may induce electrical noise on
a circuit which can interfere with normal circuit operation. |
| • | Inspect the vacuum hoses for splits or kinks. Verify that the connections
and routing are as shown on the Vehicle Emission Control Information label. Refer
to
Emission Hose Routing Diagram
. |
| • | Inspect for air leaks at the throttle body mounting and intake manifold
sealing surfaces. |
| • | Verify that the ECM grounds and the body grounds are clean, tight and
in the correct locations. Ensure the resistance between the ECM housing and the battery
negative cable is less than 0.5 ohms. |
| • | Verify that the ECM and ECM bracket fasteners are at the correct torque. |
| • | Verify the battery connections are clean and tight. |
|
Harness/Connector Inspection
|
| • | Many intermittent conditions occur with harness/connector movement caused
by vibration, engine torque, rough pavement, or component operation. Refer to
Testing for Electrical Intermittents
in Wiring Systems. |
| • | Excessive circuit resistance can cause a component to be inoperative.
If a component does not respond to a scan tool command, test the related circuits
for excessive resistance. Refer to
Testing for Continuity
in Wiring Systems. |
|
Intermittent malfunction indicator lamp (MIL) with NO DTCs
| The following conditions may cause an intermittent MIL and no DTCs:
| • | Electromagnetic interference (EMI) caused by a malfunctioning relay,
ECM controlled solenoid or switch. |
| • | The incorrect installation of non-factory or aftermarket add on accessories
such as cellular phones, alarms, lights, or radio equipment. |
| • | The malfunction indicator lamp (MIL) control circuit is intermittently
shorted to ground. |
| • | The ECM grounds are loose. |
|
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 condition 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. Inspect for water intrusion. |
| - | The condition only occurs on a cold start. |
| - | The condition goes away when the engine warms up. |
|
Duplicating Failure Conditions
|
| • | Attempt to duplicate and/or capture the failure conditions. Freeze Frame/Failure
Records data contains the conditions that are present when a DTC sets. |
| - | Operate the vehicle within the same conditions that you observed in the
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. |
| • | The scan tool can be set up to take a snapshot of parameters. 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 individually or in a combination
with other parameters for comparison. The Snapshot can be triggered manually at the
time the symptom is noticed, or set up in advance to trigger when the DTC sets. |
| | An abnormal value captured in the recorded data may point to a system or component
that requires further investigation. |
| | Refer to scan tool user instructions for more information on the Snapshot function. |
| • | 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. |
|
Additional Inspections
| Some electrical components and circuits are sensitive to EMI or other types
of electrical noise. Inspect for the following conditions:
| • | A mis-routed harness that is too close to high voltage and high current
devices such as secondary ignition components, motors, generator. These components
may induce electrical noise on a circuit that could interfere with normal circuit
operation. |
| • | Electrical system interference caused by a relay, ECM driven solenoid,
or switch. The component can cause a sharp electrical surge. Normally, the condition
occurs when the 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. |
| • | 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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