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1991 to 2013 General Motors vehicles equipped with 4L80E and 4L85E automatic transmissions often wear out the actuator feed limit (AFL) valve bore. As a result, inadequate pressure rise and shift solenoid feed oil loss can occur. This can cause trouble codes, wrong gear starts, falls out of gear and clutch plate burn-up.
The purpose of the actuator feed limit valve is to limit the pressure going to the actuators (aka solenoids). The AFL valve spring is calibrated to prevent the 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 do what they should. For example, too much pressure could flood the shift solenoids, making them act as mechanically stuck closed solenoids. Alternatively, 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 hash shifts.
- If you need the tools, order # 48-ACT-TL. this includes the boring guide, boring tool, with valves and springs
- If you already have the tools and just need the refill kit with valves and springs, order # 48-ACT-VL6
- No or low line pressure boost
- Erratic line pressure
- Wrong gear starts
- Clutch plate burn up
- Neutrals on highway
- Codes P0731, P0732, P0734, P0751 and P0756