66 Electrical System and Sensor Troubleshooting TP-6903 5/16a
4.5. Electrical System Intermittent
Problems
WARNING
Rotating parts can cause severe injury.
Stay away while the engine is in operation.
Keep hands, feet, hair, and clothing away from all moving
parts to prevent injury. Never operate the engine with
covers, shrouds, or guards removed.
WARNING
Electrical shock can cause injury.
Do not touch wires while engine is running.
Definition: The problem is not always observable and
may or may not store a Diagnostic Trouble Code
(DTC).
Use the plot function in the Spectrum software to
troubleshoot intermittent electrical problems. Set up
the plot for the sensor code that is stored in the ECM.
For example: If an intermittent Intake Air Temperature
(IAT) code is set, tag the IAT voltage and watch the
plot. While watching the plot, agitate the electrical lead
connection at the sensor and ECM connector. The
resolution of the plot screen is such that you will be able
to see any unstable voltages that you may not see with
a standard DVOM.
Figure 4-9 Electrical System Intermittent Problems Troubleshooting
Checks No
Preliminary Checks
Do not use the DTC table if a fault is intermittent. The use of the DTC tables with this
condition may result in the replacement of good parts.
Faulty Electrical Connections
or Wiring
Faulty electrical connections or wiring can cause most intermittent problems.
Check the suspected circuit for the following conditions:
Connectors poorly mated, terminals not fully seated in the connector (backed out).
Terminals not properly formed or damaged.
Lead terminals poorly connected.
Terminal tension is insufficient.
Carefully remove all the connector terminals in the problem circuit in order to ensure
the proper contact tension.
Checking for poor terminal to lead connections requires removing the terminal from the
connector body.
Operational Test
If a visual and physical check does not locate the cause of the problem, operate the
engine with Spectrum digital scan tool connected. When the problem occurs, an
abnormal voltage or scan reading indicates a problem circuit.
Intermittent DTC codes
The following components can cause intermittent DTCs:
A defective relay.
Switch that can cause electrical system interference. Normally, the problem will occur
when the faulty component is operating.
The ignition secondary voltage shorted to a ground.
The Diagnostic Test Terminal intermittently shorted to ground.
Loss of DTC Memory
To check for the loss of the DTC Memory:
Disconnect the TMAP sensor.
Run engine under no load.
The ECM should store a TMAP DTC which should remain in the memory when the
engine is turned OFF. If the TMAP DTC does not store and remain, the ECM is faulty.
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