Powertrain Control Module (PCM)

PCM Location - Under Left Hand Dash.:

DESCRIPTION
The Powertrain Control Module (PCM) uses signals from various sensors in order to optimize the control of the engine, transaxle, and electrical variable orifice power steering system. The subsystem also provides information to other subsystems and to service equipment.

The PCM is a microprocessor based computer that is the main component of the powertrain control system.

There are four different versions of the PCM:

1. Throttle body injection with manual transaxle.
2. Throttle body injection with automatic transaxle.
3. Multi-port fuel injection with manual transaxle.
4. Multi-port fuel injection with automatic transaxle.

Each powertrain control module (PCM) contains either one or two separate controllers located in one assembly. Manual transaxle versions contain only the Engine Controller (EC). The automatic transaxle versions contain an Engine Controller (EC) and a Transaxle Controller (TC). The physical size of the PCM will be the same, regardless of the number of controllers it contains.

PCM EEPROM
The PCM EEPROM stores vehicle information such as engine and transaxle calibrations. Vehicle Identification Number, programmable vehicle option content and Malf history.

Vehicle information stored on the PCM EEPROM has a major effect on how the vehicle will operate.

Reprogramming of PCM EEPROM information is necessary when replacing a PCM, or when changing the engine and/or transaxle calibrations. It is essential that a replacement PCM be reprogrammed with the correct VIN, option content, tire size, and calibration information.

The term EEPROM Reprogramming means to electronically change the contents of the Electronically Erasable Programmable Read Only Memory (EEPROM) in the PCM.

CAUTION: The EEPROM is not serviceable and should not be removed for replacement. If the PCM is removed from the vehicle, reprogramming of the EEPROM will be necessary. Reprogramming of the EEPROM is only possible with the Service Stall System (SSS) hardware available at authorized dealer locations. Check with a Saturn dealer before performing PCM or EEPROM replacement.



OPERATION

The PCM operates in two basic modes:

1. Normal operation
a. Computer and outputs operating properly and system voltage is between 6 and 16 volts.
b. Computer is operating properly, the outputs are non-functional and the system voltage is greater than 16 volts.
2. Backup operation
a. When system voltage is between 4.5 and 6 volts.
b. When system voltage is between 16 and 24 volts.
c. When the PCM is not operating properly.

NOTE: During this mode of operation the PCM will go into backup fuel operation, light the SES telltale. keep the fuel pump and electric engine cooling fan energized.