Envoy 2WD V6-4.3L VIN W (1998)
Vehicle Control Module: Component Tests and General Diagnostics
VEHICLE CONTROL MODULE DIAGNOSIS
The Diagnostic Tables incorporate diagnosis procedures using a scan tool where possible. The scan tool saves time in diagnosis. The scan tool also
prevents the replacement of good parts. In order to use the scan tool successfully for diagnosis, the technician must understand the system being
diagnosed as well as understanding the tool's limitations. Refer to Data Link Connector Diagnosis. See: Testing and Inspection
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In order to read the DTCs, use a scan tool. The technician cannot flash the DTCs by grounding the DLC. In order to clear the DTCs from the
memory, use the scan tool.
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If a diagnostic table indicates that a VCM connection or the VCM is the cause of a problem and the technician replaces the VCM but the problem
is not eliminated, one of the following items may be the reason.
1. After replacing the VCM, the Electrically Erasable Programable Read Only Memory (EEPROM) was not reprogrammed correctly. Refer to VCM
Replacement/Programming.
2. A problem may exist with the VCM terminal connections: In order to check the connections properly, remove the terminals from the connections.
NOTE: The VCM is not correct for the application: The incorrect components may cause a malfunction and may or may not set a DTC.
3. The problem is an intermittent. Make a careful physical inspection of all portions of the system involved. Refer to Symptoms.
4. A shorted solenoid, relay coil or harness may exist: The VCM turns the solenoids and relays on and off by the VCM using an internal electronic
switches called drivers. Each driver is a part of a group of 4 called quad-drivers. Failure of 1 driver can damage any other driver in the set.
5. The replacement VCM may be faulty: After replacing the VCM, recheck the system for proper operation. If the diagnostic table again indicates
that the VCM is the problem, substitute a known good VCM.
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A shorted solenoid, relay coil, or harness will not damage the quad drivers in the VCM. A shorted solenoid, relay coil, or harness will cause
the circuit and the controlled component to be inoperative.
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When the circuit fault is not present or the technician has repaired the fault, the quad driver will again operate in a normal manner due to its
fault protected design.
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If the technician has repaired a fault in the a circuit controlled by a quad-driver, reinstall the original VCM. Check the circuit for proper
operation.
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A VCM replacement is not necessary if the repaired circuit or component operates correctly.
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A J 39200 DMM provides a fast, accurate means of checking for a shorted coil or a short to battery voltage.
