A/T - No Line Pressure/Uncontrollable High Pressure
January, 1994Technical Bulletin # 209
^ Transmission: 4L80-E
^ Subject: High or low pressure
^ Application: GM, Jaguar Isuzu, Rolls Royce, Hummer
4L80-E High or Low Pressure
No line pressure rise or uncontrollable high pressure (400 psi or more) may be caused by defective or mismatched parts.
It is imperative that the case, spacer plate, and valve body gaskets be compatible to prevent complaints of very high or low pressure.
Use figures 1, 2, & 3 to positively identify the components. Once you have identified the components refer to the parts matching lists on page 2 (Figure 4).
It is also necessary to verify that the force motor is not sticking (Figure 5), and that the valve body is checked for a broken screen (Figure 5). A missing cup plug in the accumulator housing (Figure 5) can also create no line rise. Be sure to check all of these areas whenever you are looking for the cause of any high/low pressure complaints. Figure 1 - Case Identification
Figure 2 - Spacer Plate
Figure 3 - Valve Body Gasket Identification
Figure 4 - Parts Matching List
A defective force motor can also create no line rise and/or maximum mainline pressure. To determine if the force motor valve is sticking, follow the procedure.
No line rise (even with matching parts and a good force motor) may be caused by a missing cup plug in the accumulator housing.
BEWARE:
New accumulator housings may not come with a cup plug installed in the hole as shown.