Checks
| Action
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DEFINITION: The problem may or may not turn ON the Malfunction Indicator
Lamp (MIL) or store a Diagnostic Trouble Code (DTC).
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Preliminary Checks
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| • | Do not use the DTC tables. The use of the DTC tables may result
in the replacement of good parts if a fault is intermittent. |
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Faulty Electrical Connections or Wiring
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| • | Faulty electrical connections or wiring can cause most intermittent
problems. |
| • | Inspect the suspected circuit for the following conditions: |
| - | Poorly mated connectors |
| - | Terminals that are not fully seated in the connector (backed out) |
| - | Improperly formed or damaged terminals |
| - | Poor terminal to wire connections |
| • | Carefully remove all the connector terminals in the problem circuit
in order to ensure the proper contact tension. If needed, replace all the
connector terminals in the problem circuit in order to ensure the proper
contact tension. |
| • | Inspecting for poor terminal to wire connections requires removing
the terminal from the connector body. Refer to Repair Procedures in Electrical
Diagnosis in the C/K Truck Service Manual. |
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Road Test
| Drive the vehicle with the J 39200
High Impedance Multimeter or a scan tool connected to a suspected
circuit if a visual and physical inspection does not locate the cause
of the problem. An abnormal voltage or scan reading indicates the problem
may be in that circuit.
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Intermittent Malfunction Indicator Lamp (MIL)
| The following components
can cause an intermittent MIL and no DTCs:
| • | A defective relay, control module driven solenoid or a switch
that can cause an electrical system interference. This problem will normally
occur when the faulty component is operating. |
| • | The improper installation of electrical devices, such as lights,
2-way radios, electric motors, etc. |
| • | Route the Ignition Control (IC) wires away from the spark plug
wires, the ignition system components and the generator. The wire for the
engine ground from the control module to the ignition system should be
a good ground. |
| • | The ignition secondary voltage shorted to a ground. |
| • | The Malfunction Indicator Lamp (MIL) circuit or the diagnostic
test terminal intermittently shorted to ground. |
| • | The control module grounds. |
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Loss of DTC Memory
| Follow these steps in order to check for the loss of the DTC Memory:
- Disconnect the Throttle Position (TP) sensor.
- Idle the engine until the MIL illuminates.
- The VCM should store a TP sensor DTC.
- Turn the key OFF for 10 seconds.
- Start and idle the vehicle for 15 seconds.
- Turn the key OFF.
- The AF ECU should store a TP sensor DTC.
- The TP sensor DTC should remain in the memory when the ignition
is turned OFF.
- The control module is faulty if the TP sensor DTC does not store
and remain in memory.
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Additional Checks
| Check for an open diode across the A/C compressor clutch and for other
open diodes. Refer to the C/K Truck Service Manual.
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