GM Lumina/Silhouette/Transport APVs 1990-1999 Repair Guide

Powertrain Control Module

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The PCM is responsible for maintaining proper spark and fuel injection timing for all driving conditions. Ignition Control (IC) spark timing is the PCM method of controlling spark advance and ignition dwell. To provide optimum driveability and emissions, the PCM monitors input signals from the following components in calculating Ignition Control (IC) spark timing:



Igniition Control Module (ICM).
 
Engine Coolant Temperature (ECT) sensor.
 
Intake Air Temperature (IAT) sensor.
 
Transmission Range (TR) and/or Park/Neutral Position (PNP) switch.
 
Manifold Absolute Pressure (MAP) sensor.
 
Mass Air Flow (MAF) sensor.
 
Throttle Position (TP) switch.
 
Vehicle Speed Sensor (VSS)/Trans Output Speed Sensor (TOSS).
 

To allow one model of PCM to be used for many different vehicles, a device called a PROM (Programmable Read Only Memory) is used .The PROM is located inside the PCM and has information on the vehicle's weight, engine, transmission, axle ratio, and several other distinguishing characteristics. While one PCM can be used by many vehicle lines a PROM is very specific and must be used for the right vehicle.

Service of the PCM should normally consist of either replacement of the PCM or a PROM change. If the diagnostic procedures call for the PCM to be replaced, the engine "calibrator" (PROM) and the PCM should be checked first to see if they are the correct parts. If they are, remove the PROM from the faulty PCM and install it in the new PCM.

REMOVAL AND INSTALLATION



In order to prevent electrostatic discharge damage to the PCM, do not touch the connector pins or soldered components in the circuit board.

3.1L and 3.8L Engines

  1. Make sure the ignition is switched off.
  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Locate the PCM.
  6.  

See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: Location of the PCM for 3.1L and 3.8L engines is in the right hand side of the dash, behind the convenience center

  1. Carefully detach the harness connectors from the PCM (use hand tools only).
  2.  
  3. Remove the PCM from the bracket.
  4.  
  5. Since the new PCM is supplied without a PROM, care should be used when removing it from the defective PCM because it will be reused in the new PCM.
  6.  
  7. Using two fingers, push both retaining clips back away from the PROM. At the same time, grasp it at both ends and lift it up out of the socket.
  8.  
  9. Note the position of the PROM for proper installation in the new PCM. Do not remove the cover of the PROM.
  10.  

To install:
  1. When replacing the PROM, align the small notches in the PROM socket, and gently press down on the ends of the PROM until the clips are against the sides of the PROM. Now, press inward on the clips until they snap into place.
  2.  
  3. Attach the harness connectors to the PCM (use hand tools only).
  4.  
  5. Install the PCM to the bracket.
  6.  
  7. Connect the negative battery cable.
  8.  

3.4L Engine

With the advent of the 3.4L engine, the location of the Powertrain Control Module (PCM), was moved into the air cleaner housing.

  1. Make sure the ignition is switched off.
  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Remove the coolant reservoir.
  6.  
  7. Remove the SMCC module bracket.
  8.  
  9. Remove the left front strut brace.
  10.  
  11. Remove the PCM cover from the air cleaner housing.
  12.  
  13. Remove the PCM from the air cleaner housing.
  14.  

To install:

See Figure 2

Click image to see an enlarged view

Fig. Fig. 2: Exploded view of PCM Removal from Air Cleaner Housing.

  1. If a new PCM is being installed, install the KS module from the original PCM.
  2.  
  3. Install the PCM into the air cleaner housing.
  4.  
  5. Install the PCM cover to the air cleaner housing.
  6.  
  7. Install the left front strut brace.
  8.  
  9. Install the SMCC module bracket.
  10.  
  11. Install the SMCC module to the SMCC module bracket.
  12.  
  13. Install the coolant reservoir, correct the coolant level.
  14.  
  15. Connect the negative battery cable.
  16.  
  17. If a new PCM is being installed, program the EEPROM.
  18.  

 
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