Technically Speaking
- Subject: Erratic ratio control, code P1882
- Unit: VT25-E CVT
- Vehicle Application: 2005 Saturn Vue
- Essential Reading: Rebuilder, Diagnostician
- Author: Mike Riley, Transmission Digest Technical Editor
Not all codes are electrical
A 2005 Saturn Vue experiences erratic ratio control (gear position) and ultimately sets a trouble code P1882. Once the code is cleared, the transmission starts to shift again, for a short time. The code then reappears and the unit returns to a fixed gear position.
After it was determined that the issue was not computer related or valve-body/solenoid related, the transmission was removed and disassembled. Damage was found in the drive variator (pulley), and there also was seal damage.
There are two basic issues to contend with concerning CVTs. One is slippage, whether it is from the clutches (forward or reverse) or from the belt or chain. The other issue is gear change (ratio), although the change is gradual and is not like a step-type transmission. Computer strategy can make a CVT act more like a step-type transmission by merely commanding a fixed ratio position.
When a P1882 code is set and the transmission remains in a fixed position, diagnostic procedures need to be performed. With the aid of a qualified scan tool, you can determine whether the issue is internal or external. The computer could be at fault, since it has to assess the desired ratio, know the actual ratio and then command the correct ratio. The scan tool will show the actual ratio and commanded ratio, which should be close in comparison. If not, the P1882 will be set.
Provided that the computer is functioning properly, the focus should then turn to the transmission, starting with the valve body and electrical components (Figure 1). The solenoid that controls speed is the ratio-control motor (RCM), which is what moves the ratio-control (RC) lever and valve.
The RCM and RC lever/valve work in conjunction with the drive-pulley follower, which is moved by the drive pulley. Working together is what provides the correct speed (gear) (Figure 2).
The RCM can fail electrically or mechanically. For instance, if additional codes P1883, 1884, 1885 or 1886 appear, it could be an indication that the electrical coils or contacts are faulty. A resistance test can be performed through the electrical connector or directly to the RCM once it’s removed from the valve body (Figure 3). Note: The RCM bolt holes are elongated for minor adjustment. Fasten the RCM back to the same position.
Resistance between terminal 19 and all others (10, 17, 18, and 20) is about 24.0 ohms. Resistance between terminals 10/20 and 17/18 is about 47.0 ohms. The RCM is actually a mini motor with two coils that will either extend or retract the pintle. Terminals 17 and 18 are for coil number one and terminals 10 and 20 are for coil number two. Once the valve body and RCM are determined to be good, the next step is to check the drive and driven pulleys.
The primary purpose of the driven pulley is to provide the clamp force needed to keep the belt from slipping. This is accomplished through the use of hydraulic pressure and a heavy-duty apply spring, similar to the A518 overdrive spring. The other purpose of the driven pulley is to work in conjunction with the drive pulley to provide the gear ratio. Currently, the driven pulley is not rebuildable because of how it was manufactured. The pulley retainer is crimped to the pulley all the way around and requires the crimp to be cut away on a lathe, which renders it unusable (Figure 4).
The drive pulley is rebuildable and is responsible for the change in speed. The drive pulley also contains the forward clutch, which can be repaired. If the backing plate is difficult to remove, it may be due to wear in the drum at the spline area. The backing plate can wedge against the snap ring if the drum is worn (Figure 5).
Once the nut and bearing are removed from the pulley, the balance-piston housing and balance piston can then be removed. The movable pulley half and apply piston will slide off the shaft and can be inspected (Figure 6).
The pulley components need to be inspected for a couple of things. As with any clutch assembly, the seal surfaces must be smooth and the seals intact. Because of the design, the apply piston and piston bore are open, which allows contaminants to come in contact with the apply-piston seal (figures 7a and 7b). If this kind of damage is present, the pulley is unusable.
Another area to be concerned with is where the pulley slides on the shaft. There are three raceways cut into the pulley and shaft. The raceways contain six ball bearings, which keep the pulley and shaft connected and allow the pulley to slide back and forth.
The raceways can become worn and the balls can break apart eventually (figures 8a and 8b). If the wear is not too bad, dress the raceways and, instead of ball bearings, try to use three hardened rollers (0.236-inch diameter/0.562 inch long). The pins must allow the pulley to move the proper distance. With good components and new seals, reassemble the drive pulley.
When reassembling the forward clutch, rotate the backing plate one tooth if the drum is worn, so that the plate will contact good splines.
This is one example of a trouble code not being electrical.