2001 and newer Cadillac and BMW vehicles equipped with 5L40E and 5L50E automatic transmissions often wear out the actuator feed limit (AFL) and the pressure regulator (PR) valve bores.
Pressure Regulator Valve Function:
The purpose of the PR valve is to regulate the transmission line pressure. If the PR bore wear is severe enough at the balance end of the valve it can result in erratic or high line pressure. On the other hand, in those cases where the wear is most prevalent at the spring end of the valve, the leak in that area would cause erratic or low line pressure. For the same reason, the symptoms will vary as well, ranging from harsh shifts, soft shifts, burnt frictions, overheating, to converter clutch failure.
Actuator Feed Limit Valve Function:
The purpose of the AFL valve is to limit the pressure going to the actuators (aka solenoids). The AFL valve spring is calibrated to prevent the solenoid feed pressure from ever exceeding a predetermined pressure, no matter what the main line pressure is. This is necessary to prevent more fluid from being fed to the solenoids than they can physically exhaust and to limit the maximum line pressure output.
- On one hand, if the pressure feed to the ON/OFF shift solenoids is higher or lower than intended, the shift valves controlled by those solenoids may not respond accordingly. For example, too much pressure could flood the shift solenoids, making them act as mechanically stuck closed solenoids. Conversely, not enough pressure could make them act as mechanically stuck open solenoids. As a result, the transmission can have wrong gear starts, or fall out of gear.
- On the other hand, for PWM solenoids like the line pressure control solenoid (PCS), if the feed pressure is too high or too low, the consequences can be detrimental. The PCS output controls the line pressure based on the calculated load from the computer. Consequently, if the AFL pressure feeding the PCS solenoid is too high or too low, the line pressure output will also be too high or too low. As a result, the transmission will either slip and burn frictions, or have harsh shifts.
Features and benefits:
The PR valve is a precision ground hardened steel valve that is made is the USA. It has re-positioned longer lands and an internal exhaust circuit so that both ends of the valve is always supported. As a result, this new valve is a fix even with substantial bore wear. The oversized AFL valve is also a precision ground hardened steel valve that is made is the USA that features longer lands for increased durability. However, being that it requires an oversized valve, the bore needs to be reamed.
Corrects/Prevents/Reduces:
- Wrong gear starts
- Slip in 4th and 5th
- 3rd clutch failure
- Ratio codes: P0731, P0732, P0733, P0734, P0735
- No move hot
- Oil out vent
- Drain back
