G 30 Van V8-454 7.4L VIN J SFI (1996)
Engine Control Module: Component Tests and General Diagnostics
The approved procedure for diagnosing all powertrain control system faults is included in the Strategy Based Diagnostics. The preliminary checks and
the Powertrain On-board Diagnostic System Check must be performed to successfully diagnose and repair the powertrain systems. To read and clear
diagnostic trouble codes, use a scan tool. See: Powertrain Management/Computers and Control Systems/Testing and Inspection
Use a scan tool to clear diagnostic trouble codes from the VCM memory. Diagnostic trouble codes can also be cleared by turning OFF the ignition and
disconnecting the battery power from the VCM for 30 seconds, but this method will also cause all diagnostic information in the VCM memory to be
cleared and all the diagnostic tests will have to be re-run.
Since the VCM can have a failure which may affect only one circuit, following the approved diagnostic procedures will determine which circuit has a
problem and where it is. If a diagnostic table indicates that the VCM connections or VCM is the cause of a problem and the VCM is replaced. but does
not correct the problem, one of the following conditions may exist:
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There is a problem with the VCM terminal connections. The diagnostic table will indicate that the VCM connections or VCM is the problem. The
terminals may have to be removed from the VCM connector in order to check them properly.
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The EEPROM program is not correct for the application. Incorrect components may cause a malfunction and may or may not set a DTC.
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The problem is intermittent. This means that the problem is not present at the time the system is being checked. In this case, refer to Symptoms
and make a careful visual and physical inspection of all suspected components and wiring associated with the affected system. See: Powertrain
Management/Computers and Control Systems/Testing and Inspection
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There is a shorted solenoid, relay coil, or harness. Solenoids and relays are turned ON and OFF by the VCM using internal electronic switches
called drivers. Each driver is part of a group of seven called output driver modules. A shorted solenoid, relay coil, or harness will not damage the
VCM but will cause the solenoid or relay to be inoperative. The J 34636 tester, or equivalent, provides a fast, accurate means of checking for a
shorted coil or a short to battery voltage.
