Chrysler Front Wheel Drive Cars 4-CYL 1981-1995 Repair Information

Powertrain Control Module (PCM)

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Depending on the particular fuel or ignition system on your vehicle, the engine control computer may have several designations, such as: Engine Control Unit (ECU), Single Board Engine Controller (SBEC), Single Module Engine Controller (SMEC), Logic Module (LM), Power Module (PM). The term "Powertrain Control Module'' or PCM will be used in this information as a generic term meaning any of the aforementioned electronic engine controllers.

OPERATION



1981-87 Models

See Figures 1 through 12

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Fig. Fig. 1: One of the easiest ways to distinguish between the Power Module (PM) and the PCM is that the PM is equipped with two wiring connectors-a 10-way and a 12-way connector



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Fig. Fig. 2: The Logic Module (LM) is mounted behind the right-hand side, lower kick panel in the passenger's compartment-note that the MAP sensor is mounted on it



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Fig. Fig. 3: 1984-87 Chrysler Multi-point Fuel Injection (MFI) system components



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Fig. Fig. 4: 1984-87 Chrysler Electronic Fuel Injection (EFI) system components



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Fig. Fig. 5: EFI Logic Module (LM) 25-way, white electrical wiring harness connector terminal identification



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Fig. Fig. 6: EFI Logic Module (LM) 25-way, black electrical wiring harness connector terminal identification



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Fig. Fig. 7: EFI Power Module (PM) 10-way electrical wiring harness connector terminal identification



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Fig. Fig. 8: EFI Power Module (PM) 12-way electrical wiring harness connector terminal identification



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Fig. Fig. 9: MFI Logic Module (LM) 25-way, red electrical wiring harness connector terminal identification



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Fig. Fig. 10: MFI Logic Module (LM) 25-way, blue electrical wiring harness connector terminal identification



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Fig. Fig. 11: MFI Power Module (PM) 10-way electrical wiring harness connector terminal identification



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Fig. Fig. 12: MFI Power Module (PM) 12-way electrical wiring harness connector terminal identification

The fuel-injection systems on 1981-87 models do not use a single PCM to control the the engine functions; these vehicles utilize two computers: the Logic Module (LM) and the Power Module (PM).

The LM is a digital computer containing a microprocessor. The module receives input signals from various switches, sensors and components. It then computes the fuel injector pulse width, spark advance, ignition coil dwell, idle speed, purge and EGR control cycles, cooling fan and alternator.

The LM test many of its own input and output circuits. If a fault is found in a major system, this information is stored in the LM. Information on this fault can be displayed by means of the instrument panel power loss lamp or by connecting a Diagnostic Read-out Box (DRB or DRB-II) scan tool and reading the numbered display code, which directly relates to a general fault.

The Power Module (PM) contains the circuits necessary to power the ignition coil and the fuel injector(s). These are high current devices and their power supply has been isolated to minimize any "electrical noise'' reaching the LM. The PM also energizes the Automatic Shut Down (ASD) relay, which activates the fuel pump, ignition coil, injector(s), and the PM itself.

1988-95 Models

See Figures 13 through 18

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Fig. Fig. 13: 1988-95 Multi-point Fuel Injection (MFI) system components-the EFI system is the same except that it is only equipped with only one fuel injector



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Fig. Fig. 14: 1988-95 EFI Powertrain Control Module (PCM) 60-way connector terminal identification



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Fig. Fig. 15: 1988-95 MFI Powertrain Control Module (PCM) 60-way connector terminal identification



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Fig. Fig. 16A: Eagle Throttle Body Fuel Injection (TBI) system electrical schematic-Premier models (continued in Fig. 16B)



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Fig. Fig. 16B: Eagle Throttle Body Fuel Injection (TBI) system electrical schematic-Premier models (continued from Fig. 16A)



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Fig. Fig. 17: The PCM in 1988-95 models is equipped with a 60-way connector, rather than two connectors as with 1981-87 models



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Fig. Fig. 18: The PCM is mounted on the inner left-hand fender, next to the battery

The main engine computer, which controls the fuel injection system on all vehicles covered by this information, is referred to as the Powertrain Control Module (PCM). The original names coined by the manufacturer for the various engine computers differ greatly from year-to-year or model-to-model. The PCM is also known as the following: Logic Module (LM). Power Module (PM), Engine Control Unit (ECU), Single-Board Engine Controller (SBEC), Single Module Engine Controller (SMEC). Throughout this information these various computers will be referred to as simply the Powertrain Control Module (PCM).

The PCM is a digital computer containing a microprocessor. The engine computer receives input signals from various switches and sensors that are referred to as engine computer inputs. Based on these inputs, the engine computer adjusts various engine and vehicle operations through devices referred to as engine computer outputs.

The possible engine computer inputs are as follows:



Air conditioning controls
 
Battery voltage
 
Brake switch
 
Carburetor switch
 
Closed throttle switch
 
Coolant temperature sensor or switch
 
Crankshaft Position Sensor (CKPS)
 
Camshaft Position Sensor (CPS)
 
Detonation (knock) sensor
 
Engine speed sensor
 
Distributor reference pick-up
 
Manifold Absolute Pressure (MAP) sensor
 
Manifold Air Temperature (MAT) sensor
 
Methanol concentration sensor
 
Oxygen (O 2 ) sensor
 
Speed control system controls
 
Throttle position sensor
 
Throttle body temperature sensor
 
Park/Neutral switch (automatic transaxle)
 
Vehicle Speed Sensor (VSS)
 

The possible engine computer outputs are:



Air conditioning clutch relay
 
Alternator field
 
Idle Air Control Motor (IACM)
 
Auto Shutdown (ASD) and fuel pump relays
 
Canister purge solenoid
 
Malfunction indicator lamp
 
Data link connector
 
Electric EGR Transducer (EET)
 
Fuel injectors
 
Ignition coil
 
Torque converter clutch solenoid
 
Radiator fan relay
 
Speed control solenoids
 
Tachometer output
 

Based on inputs it receives, the engine computer adjusts fuel injector pulse width, idle speed, ignition spark advance, ignition coil dwell and canister purge operation. The engine computer regulates the cooling fan, air conditioning and speed control systems. The engine computer changes the alternator charge rate by adjusting the generator field.

On systems equipped with distributors, the distributor pick-up signal or, for systems without distributors, Crankshaft Position Sensor (CKPS)/Camshaft Position Sensor (CPS) is sent to the engine computer. If the engine computer does not receive a signal within approximately one second of engine cranking, the ASD relay and fuel pump relay are deactivated. When these relays are deactivated, power is shut off to the fuel injector, ignition coil, oxygen sensor heating element and fuel pump.

The engine computer contains a voltage converter that changes battery voltage to a regulated 8.0 volts. The 8.0 volts power the distributor pick-up and Vehicle Speed Sensor (VSS). The engine computer also provides a 5.0 volt supply for the coolant temperature sensor, manifold absolute pressure sensor and throttle position sensor.

REMOVAL & INSTALLATION



Except Premier Models
1981-87 MODELS-POWER MODULE

See Figures 19, 20 and 21

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Fig. Fig. 19: For 1981-87 models, remove the battery and detach the air inlet tube ...



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Fig. Fig. 20: ... detach the electrical connectors and remove the attaching screws



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Fig. Fig. 21: Remove the PM from the inner left-hand fender-note the two electrical connections

The removal and installation procedure is the same as that for the PCM in 1988-95 models; please refer to that procedure later in this section.

1981-87 MODELS-LOGIC MODULE

See Figure 2

The LM is located behind the right-hand side (passenger's side), front kick panel.

  1. Raise the hood and disconnect the negative battery cable.
  2.  
  3. Remove the right-hand side, lower kick panel.
  4.  
  5. Remove the LM mounting screws.
  6.  
  7. Remove the harness connectors from the LM, then remove it from the vehicle.
  8.  

To install:
  1. Attach the harness connectors to the LM.
  2.  
  3. Place the LM in its original position.
  4.  
  5. Install the mounting screws until secure.
  6.  
  7. Install the kick panel.
  8.  
  9. Connect the negative battery cable.
  10.  
  11. Close the hood.
  12.  

1988-95 MODELS

See Figures 22, 23, 24, 25 and 26

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Fig. Fig. 22: As with the PM, first detach the air inlet hose from the computer housing to remove the PCM



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Fig. Fig. 23: After removing the battery and tray, loosen the center bolt from the 60-way harness connector



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Fig. Fig. 24: Pull the 60-way connector out of the PCM and make sure all of the connector holes are clean



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Fig. Fig. 25: Loosen and remove the mounting screws from the PCM ...



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Fig. Fig. 26: ... then lift the PCM out of the engine bay-1988-95 models

  1. Remove the air cleaner duct or air cleaner assembly from the engine.
  2.  
  3. Remove the battery from the vehicle as described in Engine Electrical .
  4.  
  5. Remove the engine computer mounting screws.
  6.  
  7. Remove the connector(s) from the engine computer. Remove the engine computer from the vehicle.
  8.  

To install:
  1. Plug the connector(s) into the engine computer.
  2.  
  3. Install the PCM on the inside left front fender. Install and tighten the mounting screws.
  4.  
  5. Install the battery into the vehicle.
  6.  
  7. Install the air cleaner duct or air cleaner assembly.
  8.  

Premier Models

See Figure 27

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Fig. Fig. 27: The PCM (referred to as ECU in Premier models) is mounted underneath the right-hand side instrument panel

The PCM is located under the instrument panel on the passenger's side of the vehicle.

  1. Raise the hood and disconnect the negative battery cable.
  2.  
  3. Remove the PCM mounting nuts and disconnect the ground wire.
  4.  
  5. Remove the PCM from under the instrument panel.
  6.  
  7. Remove the harness connectors from the PCM.
  8.  

To install:
  1. Attach the harness connectors to the PCM.
  2.  
  3. Position the PCM over the positioning studs.
  4.  
  5. Install the ground wire and tighten the mounting nuts until secure.
  6.  
  7. Connect the negative battery cable.
  8.  
  9. Close the hood.
  10.  

 
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