GM Grand Am/Achieva/Calais/Skylark/Somerset 1985-98

Engine/Powertrain Control Module (ECM/PCM)

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OPERATION



See Figure 1

The heart of the electronic control system which is found on all vehicles covered by this information is a computer control module. The module gathers information from various sensors, then controls fuel supply and engine emission systems. Most 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 transmission vehicles or the manual upshift light on manual transmission vehicles. Later model vehicles may be equipped with a Powertrain Control Module (PCM). This is similar to the original ECM, but is designed to control additional systems as well. The PCM may control the manual transmission shift lamp or the shift functions of the electronically controlled automatic transmission.

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.



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Fig. Fig. 1: NEVER drop the Engine/Powertrain Control Module (ECM/PCM)

All of these computer control modules contain a Programmable Read Only Memory (PROM) chip, CALPAK MEM-CAL or Knock Sensor (KS) module that contains calibration information which is particular to the vehicle application. This chip is not supplied with a replacement module and must be transferred to the new module before installation. Some late models vehicles equipped with a PCM utilize both a PROM chip and an Erasable Programmable Read Only Memory (EPROM). which must be programmed with a scan tool after installation.


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 your dead battery using jumper cables.

REMOVAL & INSTALLATION



1985-97 Models

See Figures 2 through 12

  1. Turn the ignition switch OFF .
  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Remove the right side hush panel, as required.
  6.  
  7. Detach the electrical harness connectors from the computer control module.
  8.  



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Fig. Fig. 2: View of the PCM electrical connectors-1994 3.1L shown

  1. Unfasten the module-to-bracket retaining screws, then remove the ECM or PCM as applicable.
  2.  



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Fig. Fig. 3: View of the computer control module mounting-1992 3.3L shown

  1. If replacement of the calibration unit is required, unfasten the access cover retaining screws, then remove the cover from the computer control module. Carefully remove the calibration unit from the ECM/PCM, as follows:
    1. If the ECM contains a PROM carrier, use the rocker type PROM removal tool.
    2.  
    3. If the ECM contains a CAL-PAK, grasp the CAL-PAK carrier (at the narrow end only), using the removal tool. Remove the Cal-Pak carrier.
    4.  
    5. If the ECM/PCM contains a MEM-CAL or EPROM, push both retaining clips back away from the MEM-CAL/EPROM. At the same time, grasp it at both ends and lift it up out of the socket. Do not remove the cover of the MEM-CAL/EPROM.
    6.  

  2.  



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Fig. Fig. 4: In order to remove the calibration unit, you must first remove the access cover from the control module



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Fig. Fig. 5: Removing the PROM



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Fig. Fig. 6: To remove the EPROM from the PCM, push the retaining clips back away from the unit, grasping both ends, then lift it up out of the socket

Before replacement of a defective computer control module, first check the resistance of each ECM/PCM controlled solenoid. This can be done at the module connector, using an ohmmeter and the ECM or PCM connector wiring diagram. Any computer control module controlled device with low resistance will damage the replacement ECM/PCM due to high current flow through the internal circuits.

  1. On models with a Knock Sensor (KS) module in the PCM, remove performing the following procedure:
    1. Remove the access cover from the PCM.
    2.  
    3. Carefully squeeze the latches on the KS module and remover the sensor.
    4.  

  2.  



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Fig. Fig. 7: Some tabs on the PCM are pressed together ...



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Fig. Fig. 8: ... and some tabs are pressed inwards



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Fig. Fig. 9: Unscrew the access cover (1) and remove the KS sensor (2)-1996-97 3.1L shown



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Fig. Fig. 10: Some KS sensors are equipped with a gasket-1996 2.4L shown

To install:
  1. If the unit requires a Knock Sensor module, carefully insert the unit into the socket.
    1. Carefully press down the KS module until it latches.
    2.  
    3. Install the access cover and secure.
    4.  

  2.  
  3. On all other models, fit the replacement calibration unit into the socket.
  4.  

The small notch of the carrier should be aligned with the small notch in the socket. Press on the ends of the carrier until it is firmly seated in the socket. Do not press on the calibration unit, only the carrier.

  1. Install the access cover, then secure using the retaining screws.
  2.  
  3. Position the computer control module in the vehicle, then install the module-to-bracket retaining screws.
  4.  
  5. Attach the module electrical harness connectors.
  6.  
  7. Install the hush panel, as required.
  8.  
  9. Check that the ignition switch is OFF , then connect the negative battery cable.
  10.  
  11. If your vehicle has the 3.1L engine which is equipped with a PCM with EPROM, the EPROM must be reprogrammed using a 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. Enter the self-diagnostic system and check for trouble codes to be sure the module and calibration unit are properly installed. For details, refer to the procedure for checking trouble codes, later in this section.
  14.  
  15. If your vehicle is equipped with a theft-deterrent system, and has problems starting once the PCM is installed, perform the following:
    1. Attempt to start the engine.
    2.  
    3. Leave the ignition key in the ON position. The theft-deterrent lamp will flash for 10 minutes.
    4.  
    5. When the theft system lamp stops flashing, attempt to start the vehicle.
    6.  
    7. Once the engine is sucessfully running the password is learned.
    8.  

  16.  

1998 Models

See Figures 11 and 12

Because of the need for electronic equipment, EEPROM programming the PCM can only be done at a GM facility.

  1. Turn the ignition switch OFF .
  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Remove the left side hush panel, as required.
  6.  
  7. Loosen the PCM connector screws (1).
  8.  



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Fig. Fig. 11: Remove the screws (1) retaining the PCM connector on the 1998 3.1L engine

  1. Remove the PCM retainer.
  2.  
  3. Slide the PCM from the bracket.
  4.  


WARNING
Do not touch the PCM connector pins or soldered components on the circuit board. Do not remove the integrated circuit boards from the carrier.



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Fig. Fig. 12: DO NOT TOUCH THE CONNECTOR PINS ON THE PCM!-1998 3.1L engine shown

To install:
  1. Remove the PCM from its packaging and check the service number to make sure that it is the exact number or updated number as your faulty PCM.
  2.  
  3. Slide the PCM into the bracket.
  4.  
  5. Install the retainer.
  6.  
  7. Install the PCM connectors.
  8.  
  9. Tighen the screws and install the left hush panel.
  10.  
  11. Connect the negative battery cable.
  12.  
  13. Perform the EEPROM as specified.
  14.  

CKP LEARN VARIATION PROCEDURE



1998 3.1L Engine

The cranksahft position system learn variation compensating values are stored in the PCM non-volatile memory after learn procedure has been performed. If the actual crankshaft position system variation is not within the compensating values stored in the PCM, DTC P0300 may set.

The Crankshaft Position Learn Variation Procedure should be performed if any of the following conditions are true:



DTC P1336 is set
 
The PCM has been replaced
 
The PCM has been reprogrammed
 
The engine has been replaced
 
The crankshaft harmonic balancer has been replaced
 
The crankshaft position sensor has been replaced
 

 
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