Transmission CVI , what they are and what they mean
Clutch Volume Index (CVI) is a calculated numerical value to indicate how much volume of transmission fluid was needed to apply a friction element without stroking the accumulator piston. The L/R, 2/4 and OD clutch elements are continuously monitored and learned for adaptive controls. As the friction material wears, the volume of fluid needed to apply the element increases. The following numerical values are Chrysler’s suggested acceptable tolerances for A-604 clutch volumes are:
L/R: 35 to 83 2/4: 20 to 77
OD: 75 to 150 UD: 24 to 70
Early models would lose their learned values if the battery had been disconnected or the TCM was unplugged. In such cases, the EATX Controller will go to a default setting until the new CVI values are learned. The default settings used are:
L/R: 64 2/4: 48
OD: 89 UD: 45
Late model vehicles as well as updated controllers will remember the learned CVI values even if the battery has been disconnected. In these cases, the scanner may have a feature called “Battery Disconnect” (figure 1) which will erase the CVI values resetting them to the default values as seen above. These controllers will also allow you to utilize a QUICK LEARN feature (figure 2) through a scan tool to update new CVI values after an overhaul.
Earlier transaxle controllers require what is called an “Upshift Learn Procedure” otherwise known as the “Dumb Method”. This means that you have to first bring the vehicle up to operating temperature before road testing. During this road test, you must maintain constant throttle opening during the shifts and do not move the accelerator pedal during these shifts. Make 15 to 20 1-2, 2-3 and 3-4 upshifts. Accelerate from a stop each time to approximately 45 mph at an approximate throttle angle of 20-25 degrees. Next, perform what is called the “Kickdown Learn Procedure” by making 5 to 8 wide open throttle kickdowns to first gear from speeds below 25 mph. With vehicle speeds greater than 25 mph, make 5 to 8 part throttle to wide open throttle kickdowns to either 3rd or 2nd gear.
A key point in diagnosing CVI concerns is to know when they update themselves which will be explained near the end of this article.
Clutch volume indexes will update during the following shift sequence:
The L/R clutch volume updates during a 2-1 or 3-1 downshift
The 2/4 clutch volume updates during a 1-2 up-shift
The OD clutch volume updates during a 2-3 up-shift
The UD clutch volume updates during a 4-3 or 4-2 downshift
There are times when a CVI value will drop well below the minimum value. The Overdrive Clutch is one of them. This value has been known to go as low as 0 (figure 3).
If the shifts are acceptable with below minimum CVI’s, meaning the transmission does not exhibit harsh or bumpy shifts, there is no reason to be concerned. Below minimum CVI values do not cause the controller to initiate failsafe (2nd gear limp).
sequencing the release of one clutch while applying another) producing violent shifts or bumpy coast down shifts, below minimum CVI values are now a concern. The question that usually follows in this situation is what causes below minimum CVI values?
Below minimum CVI values are typically caused by internal transmission issues. Cross leaks in the valve body, over tightened clutch packs, seized accumulator pistons or excessive line pressure are examples of what could influence CVI values.
Here is where having the knowledge and understanding of when CVI values change becomes very useful in diagnosing below minimum CVI values. If they only change when they are suppose to change, this usually indicates the problem is inside the transmission. However, if they change when they are not supposed to change, there is a problem with the controller or the electrical system, i.e. the alternator.
Driving down the road in fourth gear at a highway cruise all CVI values should remain fixed. If one of them keeps dropping, check the alternator and battery. I have heard techs that drive the vehicle with the alternator disconnected as a quick test. If the CVI values no longer change they determine the alternator as the offender. If CVI values continue to change, power and grounds at the controller are good, the controller is usually faulty.
Once again, it’s good to not forget the fundamentals. Inspecting the battery system as an initial diagnosis can catch some of these off the wall issues.