Automatic transmission

The vehicles covered in this manual are equipped with a six-speed manual transmis­sion or a four, five or eight-speed automatic transmission. Information on manual trans­missions is in Part A of this Chapter. You’ll also find extension housing oil seal replace­ment, which is a virtually identical procedure for both automatic and manual transmissions, in Part A. Information on automatic transmis­sions is included in this Part of Chapter 7. Information on the transfer case is in Part C of this Chapter.

All automatic transmissions are equipped with a Torque Converter Clutch (TCC) sys­tem that engages in the higher gears. The TCC system provides a direct connection between the engine and the drive wheels, which improves fuel economy. The TCC sys­tem consists of a solenoid, controlled by the Powertrain Control Module (PCM), that locks the torque converter when appropriate.

All automatic transmissions covered in this Chapter are equipped with an exter­nal air-to-oil transmission oil cooler, which is located in front of the radiator. Diesel engines are also equipped a water-to-oil transmission cooler, which is located on the left side of the engine. On diesels, transmission fluid is routed through this water-to-oil transmission cooler first, then it’s routed through the exter­nal air-to-oil cooler.

The air-to-oil coolers used on diesel engines are equipped with an internal ther­mostat that controls the flow of transmission fluid through the cooler. When the transmis­sion fluid is below its operating temperature, it’s routed through a cooler bypass. When the fluid reaches operating temperature, the ther­mostat closes off the bypass, allowing trans­mission fluid to flow through the cooler. The thermostat can be serviced separately from the cooler (see Section 5). If you’re going to back-flush the oil cooler, the thermostat MUST be removed.

All vehicles with an automatic transmis­sion are equipped with a Brake Transmission Shift Interlock (BTSI) system that locks the shift lever in the PARK position and prevents the driver from shifting out of PARK unless the brake pedal is depressed. The BTSI sys­tem also prevents the ignition key from being turned to the LOCK or ACCESSORY position unless the shift lever is fully locked into the PARK position.

Due to the complexity of the automatic transmissions covered in this manual and the need for specialized equipment to per­form most service operations, this Chapter is limited to general diagnosis, routine mainte­nance, adjustments and removal and installa­tion procedures.

If the transmission requires major repair work, leave it to a dealer service department or a transmission repair shop. However, even if a transmission shop does the repairs, you can save some money by removing and installing the transmission yourself.