Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Clutch Volume Index (CVI)
An important function of the PCM is to monitor Transmission Clutch Volume Index (CVI). CVIs represent 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 CVIs by monitoring how long it takes for a gear change to occur. See Fig 1.
| 1 - OUTPUT SPEED SENSOR |
| 2 - OUTPUT SHAFT |
| 3 - CLUTCH PACK |
| 4 - SEPARATOR PLATE |
| 5 - FRICTION DISCS |
| 6 - INPUT SHAFT |
| 7 - INPUT SPEED SENSOR |
| 8 - PISTON AND SEAL |
Gear ratios can be determined by using the DRBIII® Scan Tool and reading the Input/Output Speed Sensor values in the "Monitors" display. 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 VOLUMES | ||||
| Clutch | When Updated | Proper Clutch Volume | ||
| Shift Sequence | Oil Temperature | Throttle Angle | ||
| L/R | 2-1 or 3-1 coast downshift | > 70° | < 5° | 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 | |
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.