Here a description and operation of a "black Box"
ECM, PCM, VCM, ETC, ETC... are all control modules.
This is a little long and might be boring so some.
**********************************************
1998 Chevy Truck K 2500 P/U ~WD V8-350 5.7L VIN R SF1 Copyright Cc 2001, ALLDATA 1-800-859-3282 5.25
Vehicle Control Module: Description and Operation With Vehicle Control Module (VCM)
VEHICLE CONTROL MODULE DESCRIPTION
The Vehicle Control Module (VCM) is located in the engine compartment. The VCM is the control center for the engine component Systems which effect engine operation. The VCM constantly monitors and processes information from the various information sensors and switches. The VCM then sends the necessary electrical responses to control the various control system components. Review the wiring diagrams in order to determine which systems are controlled by the VCM. The VCM has the ability to perform, or run, on-board diagnostic tests on itself{ the information system components, and certain control system components. The VCM has the ability to alert the driver of a malfunction by illuminating a Malfunction Indicator Lamp (MIL). The VCM has the ability to store certain information pertaining to a malfunction, including Diagnostic Trouble Codes (DTC)s. Using serial data communication, a scan tool can retrieve this information in order to be viewed by the technician. The technician can use this information in order to identify, diagnose, and verify the repair of the malfunction. The VCM is sometimes referred to as the control module.
MEMORY
The VCM control calibrations for a particular vehicle are based on the Vehicle Identification Number (VIN). The calibrations are stored in the Electrically Erasable Programmable Read Only Memory (EEPROM). The EEPROM is part of the VCM and can not be replaced. The EEPROM can be reprogrammed using the Techline equipment. The Knock Sensor (KS) module is located in the VCM. The KS module contains the KS system calibrations. The KS module is not part of the VCM and is serviced separately from the VCM. The VCM has the ability to make corrections in the fuel control system to allow for minor vehicle variations. This information is stored in the Random Access Memory (RAM). RAM needs a constant voltage supply to be retained. Short Term Fuel Trim and Long Term Fuel Trim are stored in RAM. When the battery is disconnected during service of the vehicle this memory is lost and the driver may notice a change in the performance of the vehicle. In order to restore this memory perform the following steps:
1. Start the engine.
2. Allow the engine to reach normal operating temperature.
3. Drive the vehicle under idle, partial throttle and moderate acceleration conditions.
4. Continue until normal vehicle performance returns.
CONTROL MODULE SERVICE PRECAUTIONS
IMPORTANT: Do not overload any circuit. The control module is designed to withstand the normal current draws (Amps) that are associated with the vehicle operations. Do not ground any of the control module circuits unless instructed to do so. Do not apply voltage to any of the control module circuits, when testing for an open circuit or testing for a short circuit.
NOTICE: The VCM must be maintained at a temperature below 850C (1850F) at all times. This is most critical when the vehicle is put through a paint baking process. The VCM becomes inoperative if its temperature 850C (1850F). It is recommended that temporary insulation be placed around the VCM or removed from the vehicle during the time the vehicle is in a paint oven or other high temperature process. Do not operate the vehicle if the insulation is on the VCM.
BASIC KNOWLEDGE AND TOOLS REQUIRED
In order to effectively use this service information, a general understanding of basic electrical circuits and circuit testing tools is required. The technician must be familiar with circuit diagrams and the meaning of terms such as voltage, ohms, amps, and the basic theories of electricity. The technician must understand what happens in an open circuit and a shorted circuit.
A A complete listing of the tools needed to diagnose and repair the system is located in Special Tools and Equipment.
USE OF CIRCUIT TESTING TOOLS
IMPORTANT: Do not use a test lamp in order to diagnose the control module system unless specifically instructed by the diagnostic procedures. Use the Connector Test Adapter Kit, J 35616 whenever the diagnostic procedure instructs the technician to probe any of the connectors.
NOTICE: Since the VCM is located under the hood, its connectors are sealed and cannot be backprobed as in the previous model years. Do not attempt to backprobe as a connector or seal damage could occur.
**********************************************
The new control modules can be flashed and don't need to be replaced to be reprogramed. Unless you are into and aftermarket "racing/off roading" modules.
Derek
