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.
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
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.
The PCM adjusts engine idle speed through the idle air control motor based on the following inputs:
The PCM adjusts ignition timing based on the following inputs:
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:
|Clutch||When Updated||Proper Clutch Volume|
|Shift Sequence||Oil Temperature||Throttle Angle|
|L/R||2-1 or 3-1 coast downshift||> 70||35 to 83|
|2/4||1-2 shift||> 110||5 - 54||20 to 77|
|OD||2-3 shift||48 to 150|
|UD||4-3 or 4-2 shift||> 5||24 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:
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
- Disconnect the negative battery cable.
- Raise vehicle and support.
- Remove the left front wheel.
- Remove the left front splash shield.
- Unlock and remove the 4 connectors.
- Remove the 3 mounting screws.
- Remove the PCM.
- Install the PCM.
- Install the 3 mounting screws.
- Tighten screws.
- Install and lock the 4 electrical connectors.
- Install the left front splash shield.
- Install the left front wheel.
- Lower the vehicle. Connect the negative battery cable.
|Extreme Cold||Oil temperature at start-up below -16 F||Park, Reverse, Neutral and 2nd gear only (prevents shifting which may fail a clutch with frequent shifts)|
|Cold||Oil temperature at start-up above -12 F and below 36 F||Delayed 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|
|Warm||Oil temperature at start-up above 36 F and below 80 degree F||Normal operation (Upshift, kickdowns, and coastdowns)|
|Hot||Oil temperature at start-up above 80 F||Normal operation (Upshift, kickdowns, and coastdowns)|
|Full EMCC, no PEMCC except to engage FEMCC (except at closed throttle at speeds above 70-83 mph)|
|Overheat||Oil temperature above 240 F or engine coolant temperature above 244 F||Delayed 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 Overheat||Oil temperature above 260 F||All 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