GM Camaro/Firebird 1993-1998 Repair Guide

Powertrain Control Module (PCM)

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OPERATION



See Figure 1

Whenever the term Electronic Control Module (ECM) or Powertrain Control Module (PCM) is used in this repair guide it will refer to the computer control module, regardless if the particular vehicle is equipped with a Powertrain Control Module (PCM) or Electronic Control Module (ECM).

The heart of the electronic control system, which is found on the 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 early model vehicles are equipped with an Engine Control Module (ECM) which, as its name implies, controls the engine and related emissions systems. 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 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: Typical computer control module-1995 vehicle shown

All of these computer control modules contain an Electrically Erasable Programmable Read Only Memory (EEPROM) chip, that contains calibration information which is particular to the vehicle application. When replacing the computer control module, the Electronically Erasable Programmable Read Only Memory (EEPROM) must be reprogrammed after installation. There is also 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 your dead battery using jumper cables.

In the event of a computer control module 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 module enters this mode.

Malfunction Indicator Lamp

The primary function of the MIL is to advise the operator and the technician that a fault is detected, and, in most cases, a code is stored. Under normal conditions, the malfunction indicator lamp will illuminate when the ignition is turned ON . Once the engine is started and running, the PCM will perform a system check and extinguish the lamp if no fault is found.

Additionally, the lamp can be used to retrieve stored codes after the system is placed in the Diagnostic Mode. Codes are transmitted as a series of flashes with short or long pauses. When the system is placed in the Field Service Mode, the dash lamp will indicate open loop or closed loop function to the technician.

Intermittents

If a fault occurs intermittently, such as a loose connector pin breaking contact as the vehicle hits a bump, the PCM will note the fault as it occurs and energize the dash warning lamp. If the problem self-corrects, as with the terminal pin again making contact, the dash lamp will extinguish after 10 seconds but a code will remain stored in the PCM memory.

When an unexpected code appears during diagnostics, it may have been set during an intermittent failure that self-corrected; the codes are still useful in diagnosis and should not be discounted.

REMOVAL & INSTALLATION



See Figures 2 through 11

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. It should be readily visible on the right side of the engine compartment.
  2.  
  3. Remove the computer control module mounting hardware.
  4.  
  5. Detach the electrical connectors from the control module.
  6.  



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Fig. Fig. 2: The computer control module has several electrical connectors-1996-97 5.7L engine shown



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Fig. Fig. 3: Detach the electrical connectors from the control module-1998 5.7L engine shown

  1. Remove the computer control module from the engine compartment.
  2.  



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Fig. Fig. 4: Remove the computer control module from its mounting-1993-95 vehicles



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Fig. Fig. 5: Powertrain Control Module (PCM) mounting-1996-98 3.8L engine



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Fig. Fig. 6: The computer control module is secured with two bolts-1996-97 5.7L engine



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Fig. Fig. 7: Computer control module attachment-1998 5.7L engine shown



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Fig. Fig. 8: If necessary, your can remove the module from the bracket-1993-95 vehicles

  1. Remove the control module access cover, then remove the Knock Sensor (KS) module.
  2.  

The KS module must be transferred to the replacement computer control module. Also, the replacement control module is not equipped with a EEPROM. The replacement module must be programmed before the vehicle will run.



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Fig. Fig. 9: The Knock Sensor (KS) module is located under an access cover-1993-95 vehicles



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Fig. Fig. 10: Squeeze the retaining tabs toward each other to remove the Knock Sensor (KS) module-1993-95 vehicles



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Fig. Fig. 11: Exploded view of the computer control module used on the 1993-94 5.7L engine

To install:
  1. If the control module is being replaced, perform the following:
    1. Remove the new module from its packaging to be sure the service number is the same as the defective module.
    2.  
    3. Remove the access cover.
    4.  
    5. The EEPROM must be reprogrammed using a Tech 1® or equivalent scan tool and the latest available software. Have a dealer or repair shop reprogram the module.
    6.  

  2.  
  3. Install the KS module.
  4.  
  5. Fasten the access cover on the control module.
  6.  
  7. Attach the electrical connectors to the computer control module.
  8.  
  9. Position the control module in its mounting location and secure with the mounting hardware.
  10.  
  11. Check that the ignition switch is OFF , then connect the negative battery cable.
  12.  
  13. Perform the functional check, as outlined later in this section.
  14.  
  15. For the 1998 5.7L engine, perform the idle learn procedure as outlined later in this section.
  16.  

FUNCTIONAL CHECK



  1. Using a Tech 1® or equivalent scan tool, perform the on-board diagnostic system check.
  2.  
  3. Start the engine and run for one minute.
  4.  
  5. Scan for DTC's using the Tech 1® or equivalent scan tool, as outlined later in this section.
  6.  
  7. If trouble code P0325 occurs, or if the MIL (Service Engine Soon) is ON constantly with no diagnostic trouble codes, the KS module is not fully seated or is defective.
  8.  
  9. If it is not fully seated, press firmly on the ends of the KS module.
  10.  

IDLE LEARN PROCEDURE



Anytime the computer control module or battery is disconnected or the module loses power, the control module's learns position of the Idle Air Control (IAC) valve pintle is lost. The engine idle is unstable when the pintle position is lost, therefore the following procedure must be performed to return the IAC valve pintle to the correct position.

Vehicles Equipped with Automatic Transmissions
  1. Make sure the ignition is in the OFF position.
  2.  
  3. Restore the PCM battery feed.
  4.  
  5. Turn OFF the A/C controls.
  6.  
  7. Set the parking brake and block the drive wheels.
  8.  
  9. Start the engine.
  10.  
  11. Shift the transmission into D.
  12.  
  13. Allow the engine to idle for 10 minutes.
  14.  
  15. Turn the A/C controls ON.
  16.  
  17. Allow the engine to idle for 10 minutes.
  18.  
  19. Shift the transmission into P.
  20.  
  21. Allow the engine to idle for 10 minutes.
  22.  
  23. Turn the A/C controls OFF.
  24.  
  25. Allow the engine to idle for 10 minutes.
  26.  
  27. Turn the engine OFF for 30 seconds.
  28.  

Vehicles Equipped with Manual Transmissions
  1. Make sure the ignition is in the OFF position.
  2.  
  3. Restore the PCM battery feed.
  4.  
  5. Turn OFF the A/C controls.
  6.  
  7. Set the parking brake and block the drive wheels.
  8.  
  9. Make sure the transmission is in N.
  10.  
  11. Start the engine.
  12.  
  13. Turn the A/C controls ON.
  14.  
  15. Allow the engine to idle for 10 minutes.
  16.  
  17. Turn the A/C controls OFF.
  18.  
  19. Allow the engine to idle for 10 minutes.
  20.  
  21. Turn the engine OFF for 30 seconds.
  22.  

 
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