ParkAvenue 1997-1999

Electronic Control Module

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Operation



Specific to:

Buick LeSabre 1986-1999

Buick Park Avenue 1996-1999

Oldsmobile 88 1992-1999

Oldsmobile Delta 88 1986-1988

Oldsmobile LSS 1996-1999

Pontiac Bonneville 1987-1999

The heart of the electronic control system, which is found on the vehicles covered by this manual, is a computer control module. The module gathers information from various sensors, then controls fuel supply and engine emission systems. Most early model vehicles are equipped with an Engine Control Module (ECM) which, as its name implies, controls the engine and related emissions systems. Some ECMs may also control the Torque Converter Clutch (TCC) on automatic transaxle vehicles. Later model vehicles may be equipped with a Powertrain Control Module (PCM). This is similar to the original ECMs, but is designed to control additional systems as well. The PCM may control the manual transaxle shift lamp or the shift functions of the electronically controlled automatic transaxle.

Regardless of the name, all computer control modules are serviced in a similar manner. Care must be taken when handling these expensive components in order to protect them from damage. Carefully follow all instructions included with the replacement part. Avoid touching pins or connectors to prevent damage from static electricity.

All of these computer control modules contain a Programmable Read Only Memory (PROM) chip, MEM-CAL or EEPROM that contains calibration information specific to the vehicle application. For all applications except those equipped with an EEPROM, this chip is not supplied with a replacement module, and must be transferred to the new module before installation. If equipped with an Electronically Erasable Programmable Read Only Memory (EEPROM), it must be reprogrammed after installation. Some later model vehicles have a Knock Sensor (KS) module, mounted in the PCM. The KS module contains the circuitry that allows the PCM to utilize the Knock Sensor signal to diagnose the circuitry.


WARNING
To prevent the possibility of permanent control module damage, the ignition switch MUST always be OFF when disconnecting power from or reconnecting power to the module. This includes unplugging the module connector, disconnecting the negative battery cable, removing the module fuse or even attempting to jump start your dead battery using jumper cables.

In the event of an ECM failure, the system will default to a pre-programmed set of values. These are compromise values which allow the engine to operate, although at a reduced efficiency. This is variously known as the default, limp-in or back-up mode. Driveability is almost always affected when the ECM enters this mode.

Removal & Installation



Specific to:

Buick LeSabre 1986-1995

Buick Park Avenue 1996-1999

Oldsmobile 88 1992-1995

Oldsmobile Delta 88 1986-1988

Pontiac Bonneville 1987-1995

On these vehicles, the computer control module is located in the engine compartment, in front of the right side shock tower.

  1. Make sure the ignition switch is turned OFF , then disconnect the negative battery cable.
  2.  


CAUTION
To prevent the possibility of permanent control module damage, the ignition switch MUST always be OFF when disconnecting power from or reconnecting power to the module. This includes unplugging the module connector, disconnecting the negative battery cable, removing the module fuse or even attempting to jump your dead battery using jumper cables.

  1. Locate the computer control module. On these vehicles, the module is mounted inside the passenger compartment, under the dash.
  2.  
  3. Remove the interior access panel/right side hush panel.
  4.  
  5. Carefully detach the harness connectors from the ECM.
  6.  
  7. Remove the ECM-to-bracket retaining screws and remove the ECM, then remove the ECM from its mounting position.
  8.  



Click image to see an enlarged view

Fig. On 1987-95 vehicles, the control module is located behind the right side of the instrument panel



Click image to see an enlarged view

Fig. Exploded view of the ECM mounting to the instrument panel - 1991 vehicle shown, others similar



Click image to see an enlarged view

Fig. View of the computer control module and its MEM-CAL or PROM access panel

To install:

  1. If the module is being replaced, CAREFULLY replace the PROM chip, MEM-CAL or Knock Sensor (KS) module, as outlined later in this section.
  2.  
  3. Position the ECM in the vehicle and install the ECM-to-bracket retaining screws.
  4.  
  5. Attach the ECM harness connectors.
  6.  
  7. Install the hush panel/interior access panel.
  8.  
  9. Check that the ignition switch is OFF , then connect the negative battery cable.
  10.  
  11. If equipped with a computer control module that contains an EEPROM, it must be reprogrammed using a Tech 1® or equivalent scan tool and the latest available software. In all likelihood, the vehicle must be towed to a dealer or repair shop containing the suitable equipment for this service.
  12.  
  13. Perform the functional check, as outlined later in this section.
  14.  

Specific to:

Buick LeSabre 1996-1999

Buick Park Avenue 1996-1999

Oldsmobile 88 1996-1999

Oldsmobile LSS 1996-1999

Pontiac Bonneville 1996-1999

On these vehicles, the computer control module is located in the engine compartment, in front of the right side shock tower, above the EVAP canister.

  1. Make sure the ignition switch is turned OFF , then disconnect the negative battery cable.
  2.  


CAUTION
To prevent the possibility of permanent control module damage, the ignition switch MUST always be OFF when disconnecting power from or reconnecting power to the module. This includes unplugging the module connector, disconnecting the negative battery cable, removing the module fuse or even attempting to jump your dead battery using jumper cables.

  1. Locate the computer control module. On these vehicles it is located in the engine compartment, in front of the right side shock tower, above the EVAP canister.
  2.  
  3. If equipped with an engine compartment mounted module, one or all of the following steps may be necessary:
    1. Remove the coolant tank reservoir.
    2.  
    3. Remove the air cleaner intake duct.
    4.  
    5. Remove the right side splash shield.
    6.  
    7. Unfasten the retainers and remove the plastic PCM cover/sight shield.
    8.  

  4.  
  5. Partially lift the PCM up from the mounting bracket, then carefully detach the harness connectors from the PCM.
  6.  



Click image to see an enlarged view

Fig. Exploded view of the PCM sight shield (1), harness connector (2), PCM (3) and mounting bracket (4)

To install:

  1. Remove the PCM from the engine compartment. If the PCM is being replaced, CAREFULLY transfer the KS module to the new PCM, as outlined later in this section.
  2.  
  3. Position the PCM in the mounting bracket.
  4.  
  5. Attach the PCM harness connectors.
  6.  
  7. For engine compartment mounted modules, install the following components, as applicable.
    1. Plastic ECM cover/sight shield and secure with the retainers.
    2.  
    3. Right side splash shield.
    4.  
    5. Air cleaner intake duct.
    6.  
    7. Coolant tank reservoir.
    8.  

  8.  
  9. Check that the ignition switch is OFF , then connect the negative battery cable.
  10.  
  11. If equipped with a computer control module that contains an EEPROM, it must be reprogrammed using a Tech 1® or equivalent scan tool and the latest available software. In all likelihood, the vehicle must be towed to a dealer or repair shop containing the suitable equipment for this service.
  12.  
  13. Perform the functional check, as outlined later in this section.
  14.  

 
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