Pacifica, 2003-2005

Powertrain Control Module



PCM Ground

Ground is provided through multiple pins of the PCM connector. Depending on the vehicle there may be as many as two different ground pins. There are power grounds and sensor grounds.

The power grounds are used to control the ground side relays, solenoids, ignition coil or injectors. The signal ground is used for any input that uses sensor return for ground, and the ground side of any internal processing component.

The PCM case is shielded to prevent RFI and EMI. The PCM case is grounded and must be firmly attached to a good, clean body ground.

Internally all grounds are connected together, however there is noise suppression on the sensor ground. For EMI and RFI protection the housing and cover are also grounded separately from the ground pins.

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PCM Inputs

Air Conditioning Pressure Transducer
Ambient temperature Sensor
ASD Relay
Battery Temperature Sensor (NGC)
Battery Voltage
Brake Switch
Camshaft Position Sensor
Crankshaft Position Sensor
EGR Position Feedback
Engine Coolant Temperature Sensor
Heated Oxygen Sensors
Ignition sense
Intake Air Temperature Sensor
Knock Sensor
NVLD Assembly
Manifold Absolute Pressure (MAP) Sensor
Power Steering Pressure Switch
EVAP Purge Return
SCI Receive
Speed Control
Throttle Position Sensor
Transmission Control Relay (Switched B+)
Transmission Pressure Switches
Transmission Temperature Sensor
Transmission Input Shaft Speed Sensor
Transmission Output Shaft Speed Sensor
Transaxle Gear Engagement
Vehicle Speed

PCM Inputs & Outputs

The Powertrain Control Module (PCM) is a digital computer containing a microprocessor. The PCM receives input signals from various switches and sensors referred to as Powertrain Control Module Inputs. Based on these inputs, the PCM adjusts various engine and vehicle operations through devices referred to as Powertrain Control Module Outputs.

PCM Outputs

Air Conditioning Clutch Relay
Automatic Shut Down (ASD) and Fuel Pump Relays
Data Link Connector (PCI and SCI Transmit)
Double Start Override
EGR Solenoid
Fuel Injectors
Generator Field
High Speed Fan Relay
Idle Air Control Motor
Ignition Coils
NVLD Assembly
Low Speed Fan Relay
MTV Actuator
EVAP Purge
SRV Valve
Speed Control Vent Solenoid
Speed Control Vacuum Solenoid
5-Volt Output
Torque Reduction Request
Transmission Control Relay
Transmission Solenoids
Vehicle Speed

Based on inputs it receives, the powertrain control module (PCM) adjusts fuel injector pulse width, idle speed, ignition timing, and canister purge operation. The PCM regulates the cooling fans, air conditioning and speed control systems. The PCM changes generator charge rate by adjusting the generator field.

The PCM adjusts injector pulse width (air-fuel ratio) based on the following inputs.

Battery Voltage
Intake Air Temperature Sensor
Engine Coolant Temperature
Engine Speed (crankshaft position sensor)
Exhaust Gas Oxygen Content (heated oxygen sensors)
Manifold Absolute Pressure
Throttle Position

The PCM adjusts engine idle speed through the idle air control motor based on the following inputs:

Brake Switch
Engine Coolant Temperature
Engine Speed (crankshaft position sensor)
Transaxle Gear Engagement
Throttle Position
Vehicle Speed

The PCM adjusts ignition timing based on the following inputs:

Intake Air Temperature
Engine Coolant Temperature
Engine Speed (crankshaft position sensor)
Knock Sensor
Manifold Absolute Pressure
Transaxle Gear Engagement
Throttle Position

The automatic shut down (ASD) and fuel pump relays are mounted externally, but turned on and off by the powertrain control module through the same circuit.

The camshaft and crankshaft signals are sent to the powertrain control module. If the PCM does not receive both signals within approximately one second of engine cranking, it deactivates the ASD and fuel pump relays. When these relays are deactivated, power is shut off to the fuel injectors, ignition coils, fuel pump and the heating element in each oxygen sensor.

The PCM engine control strategy prevents reduced idle speeds until after the engine operates for 320 km (200 miles). If the PCM is replaced after 320 km (200 miles) of usage, update the mileage in new PCM. Use a proper scan tool to change the mileage in the PCM.

Transmission Control

Clutch Volume Index (CVI)

An important function of the PCM is to monitor Clutch Volume Index (CVI). CVI represents the volume of fluid needed to compress a clutch pack. The PCM monitors gear ratio changes by monitoring the Input and Output Speed Sensors. The Input, or Turbine Speed Sensor sends an electrical signal to the PCM that represents input shaft rpm. The Output Speed Sensor provides the PCM with output shaft speed information.

By comparing the two inputs, the PCM can determine transaxle gear ratio. This is important to the CVI calculation because the PCM determines CVI by monitoring how long it takes for a gear change to occur. Using a proper scan tool and reading the Input/Output Speed Sensor values in the scan tool display can determine gear ratios. Gear ratio can be obtained by dividing the Input Speed Sensor value by the Output Speed Sensor value.

For example, if the input shaft is rotating at 1000 rpm and the output shaft is rotating at 500 rpm, then the PCM can determine that the gear ratio is 2:1. In direct drive (3rd gear), the gear ratio changes to 1:1. The gear ratio changes as clutches are applied and released. By monitoring the length of time it takes for the gear ratio to change following a shift request, the PCM can determine the volume of fluid used to apply or release a friction element.

The volume of transmission fluid needed to apply the friction elements are continuously updated for adaptive controls. As friction material wears, the volume of fluid need to apply the element increases.

Certain mechanical problems within the clutch assemblies (broken return springs, out of position snap rings, excessive clutch pack clearance, improper assembly, etc.) can cause inadequate or out-of-range clutch volumes. Also, defective Input/Output Speed Sensors and wiring can cause these conditions. The following chart identifies the appropriate clutch volumes and when they are monitored/updated:

ClutchWhen UpdatedProper Clutch Volume
Shift SequenceOil TemperatureThrottle Angle
L/R2-1 or 3-1 coast downshift> 70   35 to 83
2/41-2 shift> 1105 - 5420 to 77
OD2-3 shift48 to 150
UD4-3 or 4-2 shift> 524 to 70

Shift Schedules As mentioned earlier, the PCM has programming that allows it to select a variety of shift schedules. Shift schedule selection is dependent on the following:

Shift lever position
Throttle position
Engine load
Fluid temperature
Software level

As driving conditions change, the PCM appropriately adjusts the shift schedule. Refer to the SHIFT Operation chart to determine the appropriate operation expected, depending on driving conditions.

Removal & Installation

  1. Disconnect the negative battery cable.
  3. Raise vehicle and support.
  5. Remove the left front wheel.
  7. Remove the left front splash shield.
  9. Unlock and remove the 4 connectors.
  11. Remove the 3 mounting screws.
  13. Remove the PCM.

To Install:

The PCM connectors are color-coded.

  1. Install the PCM.
  3. Install the 3 mounting screws.
  5. Tighten screws.
  7. Install and lock the 4 electrical connectors.
  9. Install the left front splash shield.
  11. Install the left front wheel.
  13. Lower the vehicle. Connect the negative battery cable.

ScheduleConditionExpected Operation  
Extreme ColdOil temperature at start-up below -16 FPark, Reverse, Neutral and 2nd gear only (prevents shifting which may fail a clutch with frequent shifts)  
ColdOil temperature at start-up above -12 F and below 36 FDelayed 2-3 Upshift (approximately 22-31 mph)  
Delayed 3-4 Upshift (45-53 mph)  
Early 4-3 coastdown shift (approximately 30 mph)  
Early 3-2 coastdown shift (approximately 17 mph)  
High speed 4-2, 3-2, 2-1 kickdown shifts are prevented  
WarmOil temperature at start-up above 36 F and below 80 degree FNormal operation (Upshift, kickdowns, and coastdowns)  
HotOil temperature at start-up above 80 FNormal operation (Upshift, kickdowns, and coastdowns)  
Full EMCC, no PEMCC except to engage FEMCC (except at closed throttle at speeds above 70-83 mph)  
OverheatOil temperature above 240 F or engine coolant temperature above 244 FDelayed 2-3 Upshift (25-32 mph)  
Delayed 3-4 Upshift (41-48 mph)  
3rd gear FEMCC from 30-48 mph  
3rd gear PEMCC from 27-31 mph  
Super OverheatOil temperature above 260 FAll Overheat shift schedule features apply  
2nd gear PEMCC above 22 mph  
Above 22 mph the torque converter will not unlock unless the throttle is closed or if a wide open throttle 2nd PEMCC to 1 kickdown is made  

Shift Operation Chart

Click image to see an enlarged view