Slipping or No Fourth Gear

WARNING: This page is about a different car, the 2004 Pontiac Aztek and 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.

Checks	Cause
DEFINITION: A large engine RPM increase is noted in fourth gear, Drive range, with little or no vehicle forward speed increase. First, second, and third gear operation are normal. Shifts into fourth gear are soft or do not occur. Fourth gear ratio is 0.705:1.
Automatic Transmission Fluid Level	Low fluid level
Transmission Main Line Pressure	Low transmission main line pressure
Oil Filter Assembly	The oil filter assembly (100) is missing, plugged, or damaged. The oil filter seal assembly (101) is missing or is damaged.
Control Valve Body Assembly	The 3-4 shift valve (362) or the 4-3 manual downshift valve (360) is stuck or binding. Debris is found in the passages of the control valve body (301) or of the control valve body spacer plate and gasket assembly (396)
Case Cover Assembly	Distortion or damage occurs at the manual valve (404) or at the case cover (401), causing PRN oil leak.
Driven Sprocket Support Assembly	A plugged third clutch oil passage in the driven sprocket support assembly (609)
Fourth Clutch Assembly	The clutch plates (500-502) are worn, damaged, or misassembled. A missing or not seated fourth clutch spring retaining ring (601) A damaged spring assembly (602) or piston (603) Worn or damaged fourth clutch piston seals (604, 605)
Third Clutch Sprag Assembly	The sprag (720) was misassembled or backwards on the inner race (661). A damaged third clutch sprag assembly (653, 661, 719-721)