C 2500 Truck 2WD V8-5.7L VIN R (1997)
Engine Control Module: Description and Operation
GENERAL DESCRIPTION
The VCM is located on the right hand side fenderwell. The VCM is the control center for the fuel, emissions, ignition, and automatic transmission
control functions.
The VCM constantly monitors the information from the various sensors. The VCM controls the component systems which affect the engine
operation.
The VCM alerts the driver through the Malfunction Indicator Lamp (MIL) or the antilock indicator lamp. The VCM stores the DTCs which
identify the problem areas for the technician making repairs. Refer to Vehicle Control Module, for further information on using the diagnostic
function of the VCM for engine operation.
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Refer to Transmission for the diagnosis of the automatic transmission.
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Refer to Anti-lock brakes for diagnosis of the brake system.
The VCM in this vehicle is programmable. The only services allowed on the VCM is the control module replacement with the Knock Sensor (KS)
calibrator Programmable Read Only Memory (PROM) transferred or the KS calibrator PROM only.
The KS calibrator contains the up integrated knock sensor calibration. The VCM stores the 4 calibrations in the Electronically Erasable
Programmable Read Only Memory (EEPROM).
When replacing the VCM, programming the EEPROM and transferring the KS calibrator PROM to the new VCM is mandatory. Refer to the
EEPROM Programming. Refer to VCM Replacement/Programming.
The 4 calibrations required for the VCM are the Powertrain, the ABS, the VSS buffer, and the A/C. Each calibration has its own part number.
Determine the correct calibrations for a particular vehicle based on the VIN number of the vehicle.
MALFUNCTION INDICATOR LAMP (MIL)
The MIL (Malfunction Indicator Lamp) is on the instrument panel. The MIL has the following functions:
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The MIL informs the driver that a fault that affects the vehicle's emission levels has occurred. The owner should take the vehicle for service as
soon as possible.
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As a bulb and system check, the MIL (Malfunction Indicator Lamp) comes on with the key on and the engine not running. When the engine is
started, the MIL turns off if no DTCs are set.
When the MIL remains on while the engine is running, or when a malfunction is suspected due to a driveability or emissions problem, perform an
On-Board Diagnostic (OBD) System Check. The procedures for these checks are given in engine controls. These checks expose faults which the
technician may not detect if other diagnostics are performed first.
DIAGNOSTIC INFORMATION
The diagnostic Tables and functional checks are designed to locate a faulty circuit or component through a process of logical decisions. The
Tables are prepared with the assumption that the vehicle functioned correctly at the time of assembly and that there are not multiple faults present.
There is a continuous self-diagnosis on certain control functions. This diagnostic capability is complemented by the diagnostic procedures
contained in this manual. The language of communicating the source of the malfunction is a system of diagnostic trouble codes. When a
malfunction is detected by the control module, a diagnostic trouble code will set and the Malfunction Indicator Lamp (MIL) Malfunction Indicator
Lamp will illuminate on some applications.
VCM LEARNING ABILITY
WARNING: 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 VCM's learning ability allows it to make corrections for minor variations in the fuel system in order to improve driveability. When the battery
is disconnected for other repairs, the learning process resets. The driver my note a change in the vehicle's performance. In order to teach the
vehicle ensure that the engine is at the operating temperature. Drive the vehicle at part throttle with a moderate acceleration and idle conditions
until normal performance returns.
INPUT INFORMATION
The VCM processes the various input information. Then the VCM sends the necessary electrical responses to the control fuel delivery, the spark
timing, and the other emission control systems. The input information interrelates to more than one output; therefore, if the one input fails, the
failure can affect more than one system's operation.
PROM (KS Module)
This assembly contains an electronic Knock Sensor (KS) module.
