Saturn Coupes/Sedans/Wagons 1991-1998 Repair Guide

Powertrain Control Module (PCM)

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OPERATION



The PCM is located in the upper dashboard area, in back of the instrument cluster assembly. The PCM utilizes signals from a variety of sensors to optimize control of the engine, transaxle and various accessories. The PCM is a microprocessor-based computer that is the main component of the powertrain control system. The PCM contains either one or two separate controllers located in one unit. The manual transaxle version contains only an engine controller, while the automatic transaxle version contains both an engine and transaxle controller.

The PCM contains an Electronicaly Erasable Programmable Read Only Memory (EEPROM), which stores information necessary for proper vehicle operation. Whenever the PCM is replaced, this memory must be reprogrammed in order for the vehicle to operate. The vehicle may not even start if this is not done. Only a dealer/serivce station equipped with the Saturn Service Stall System, or an equivalent EEPROM reprogramming computer, will be able to properly calibrate the PCM.

The PCM module contains a built-in learning ability that allows it to maximize driveability by correcting for minor variations in the fuel system. Any time the PCM is replaced or the power is removed from the PCM, the module must go through a relearning process. Maximum performance may not return until after this is accomplished. To enable the PCM to relearn the fuel system:

  1. Start the vehicle and warm it to normal operating temperature.
  2.  
  3. Drive the vehicle at part throttle, with moderate acceleration and idle conditions, until normal performance returns.
  4.  
  5. Park the vehicle and engage the parking brake.
  6.  
  7. For automatic transaxles, shift into D . For manual transaxles, shift into N .
  8.  
  9. Allow the engine to idle at normal operating temperature for about 2 minutes, until the engine stabilizes.
  10.  

REMOVAL & INSTALLATION



1991-94 Models

See Figure 1

  1. If equipped, properly disable the SIR system as follows:
    1. Align the steering wheel so the tires are in the straight-ahead position, then turn the ignition OFF .
    2.  
    3. Remove the SIR fuse from the Instrument Panel Junction Block (IPJB).
    4.  
    5. Remove the Connector Position Assurance (CPA), then detach the yellow 2-way SIR connector at the base of the steering column.
    6.  

  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Remove the driver' side kick panel and/or the knee bolster for access to the PCM.
  6.  
  7. Rotate the retaining screw 1 / 4 turn counterclockwise and remove the PCM from the carrier.
  8.  
  9. Unplug the electrical connectors from the PCM and remove the unit from the vehicle.
  10.  

To install:
  1. Install the wiring harness connectors to the PCM, then position the unit into the carrier. </