GM Cavalier/Sunbird/Skyhawk/Firenza 1982-1994

Engine/Powertrain Control Module (ECM/PCM)

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OPERATION



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.

All of these computer control modules contain a Programmable Read Only Memory (PROM) chip, CALPAK or MEM-CAL 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 model vehicles equipped with a 3.1L engine utilize both a PROM chip and an Erasable Programmable Read Only Memory (EPROM), which must be programmed with a scan tool after installation. On these models, it is recommended for this procedure to be performed at a properly equipped, reputable shop.


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



See Figures 1, 2, 3 and 4

  1. Turn the ignition switch OFF .
  2.  



Click image to see an enlarged view

Fig. Fig. 1: On most models, the ECM/PCM is located inside the vehicle

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the right side hush panel, glove box or interior access panel, as required for access to the control module.
  4.  
  5. Detach the electrical harness connectors from the computer control module.
  6.  



Click image to see an enlarged view

Fig. Fig. 2: In order to remove the calibration unit, you must first remove the access cover from the control module - 1992 vehicle shown



Click image to see an enlarged view

Fig. Fig. 3: Removing the PROM using the special rocker tool



Click image to see an enlarged view

Fig. Fig. 4: 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

  1. Unfasten the module-to-bracket retaining screws, then remove the ECM or PCM as applicable.
  2.  
  3. 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, EPROM or KS Module, 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/KS module.
    6.  

  4.  

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.

To install:
  1. Fit the replacement calibration unit into the socket.
  2.  

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 right side hush panel, glove box or interior access 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.  

FUNCTIONAL CHECK



  1. Turn the ignition switch ON .
  2.  
  3. Enter diagnostics, by grounding the appropriate ALDL terminals. Refer to diagnostics procedures in this section.
  4.  
  5. Allow Code 12 to flash 4 times to verify that no other codes are present. This indicates the PROM or MEM-CAL is installed properly.
  6.  
  7. If trouble Codes 42, 43 or 51 are present or if the SERVICE ENGINE SOON light is on constantly with no codes, the PROM/MEM-CAL is not fully seated, installed backward, has bent pins or is defective.
  8.  

Anytime the calibration unit is installed backward and the ignition switch is turned ON, the unit is destroyed.

  1. If it is not fully seated, press firmly on the ends of the MEM-CAL.
  2.  

 
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