DeVille V8-4.6L VIN 9 (1995)
Powertrain Control Module: Description and Operation
Powertrain Control Module PROM
PCM And PROM View
DESCRIPTION
NOTICE: Electrostatic Discharge (ESD) sensitive component. Follow handling and measuring precautions listed in Diagrams/Diagnostic
Aids/Handling and Measuring Procedures.
To allow one Powertrain Control Module (PCM) to be used for many different cars, a device called a Programmable Read Only Memory unit, or
PROM, is used. The PROM, which is located inside the PCM (refer to image), contains the calibration information used by the PCM to control
fueling, idle speed, cruise control, ignition timing, transaxle shifts and cooling fans. This calibration information is based on various aspects of the
vehicle such as engine size, vehicle weight, transaxle, axle ratio and numerous others. While the PCM contains two separate processors to control
various functions, the PROM contains two separate PROM'S. Each PROM provides specific information to one of the processors of the PCM.
However, the PROM's are physically connected and form one larger PROM, making them serviceable only as a unit.
VEHICLE SPECIFIC PROM
While one PCM can be used for several different vehicles, the PROM is very specific and can only be used for certain applications. Therefore, the
PCM is serviced separately from the PROM, even though the PROM is housed inside the PCM. It is very important to check the latest parts book and
serviceman bulletin information for the correct part number when replacing the PROM. Parameters PD97 and PD99 can be used to verify the proper
PROM I.D.
REPLACEMENT PCM
Replacement PCM's used for service come without a PROM. Therefore, the PROM from the old PCM must be carefully removed and installed in the
new PCM (Refer to PROM Removal). If the PROM is missing, it will result in a no start, no run condition, and the PCM will not send data to the
Instrument Panel Cluster (IPC). A current Code I034 and a SYSTEM PROBLEM message on the Driver Information Center(DIC) will result.
