DeVille V8-4.6L VIN 9 (1995)
Powertrain Control Module: Description and Operation
Powertrain Control Module (PCM)
PCM And PROM View
DESCRIPTION
The Powertrain Control Module (PCM), shown in the accompanying image, controls fueling, idle speed, exhaust emissions, transaxle shifts, ignition
timing, cooling fans and cruise control functions. The PCM can also recognize operational problems, alert the driver through the SERVICE ENGINE
SOON Malfunction Indicator Lamp (MIL) and store codes which identify problem areas for the technician. Refer to System Diagnosis / Procedures
/ Vehicle On-Board Diagnostics for more information on using the diagnostic function of the PCM.
PCM PROCESSORS
In order to perform all of these functions, the PCM contains two processors, each with its own outputs, inputs, memory and program. The two
processors function together by sharing input data, but they also function independently by controlling only certain outputs. The functions of each
processor can be loosely categorized as engine controls or transaxle controls. The only functions performed by both processors is the diagnosis of the
serial data line, battery power circuits, and the PCM PROM. Because each processor diagnoses these on their own, each sets its own code in the case
of a failure. For example, each time the battery is disconnected, two Diagnostic Trouble Codes (DTCs) will set, P052 and PI09.
PCM HARNESS CONNECTORS
The PCM is connected to the engine wiring harness by three 32-pin connectors. Each connector is color coded - red, white, or blue - and each row of
pins in these three connectors has been given a unique alphabetical designation: A or B (red connector), C or D (white connector), or E or F (blue
connector). Refer to Diagrams / Connector Views under this heading for PCM connector pinouts.
PCM SERVICEABLE PARTS
The PCM consists of two separately serviceable parts: the PCM and the PCM PROM. The PROM plugs into the PCM and is located under the
PROM cover.
PCM EEPROM
The PCM contains a data storage unit which can save critical data even when battery power is removed. This unit, the Electrically Erasable
Programmable Read Only Memory (EEPROM) is used by the PCM to store Throttle Position (TP) Sensor/Idle learned values, Transaxle Shift
Adapt values, Transaxle Oil Life Index, and Cruise Control Lash/Learn.
These values are stored in the EEPROM during the first 30 seconds after the key is turned OFF. Therefore, you should wait at least 30 seconds after
key OFF before disconnecting the battery to allow these values to be stored in the EEPROM.
IMPORTANT: Disconnecting the battery before the PCM is able to store the values may result in EEPROM reset, DTC P080 and transaxle oil life
being reset to zero.
The EEPROM is soldered into the PCM and cannot be serviced separately.
