General Description

45RFE / 545RFE ELECTRONIC TRANSMISSION
The 45RFE/545RFE electronic transmission is a conventional transmission in that it uses hydraulically applied clutches to shift a planetary gear train. However, the electronic control system replaces many of the mechanical and hydraulic components used in conventional transmission valve bodies.

The 45RFE/545RFE electronic transmission is a fully electronically controlled transmission. The Transmission Control Module (TCM) is similar to (but not the same as) the one used in the 41TE and 42LE transmissions, therefore many similarities exist in function and diagnosis.

The 45RFE/545RFE Transmission family can be identified by confirming the presence of a 23 pin electrical connector on the left hand side of the transmission oriented vertically near the manual lever.

The 45RFE/545RFE has an overrunning clutch (used in 1st gear), an electronically controlled torque converter clutch, 3 planetary gearsets, and six clutch packs. The clutches are called 2nd Clutch (2C), 4th Clutch (4C), Low/Reverse Clutch (LR), Reverse Clutch (RC), Underdrive Clutch (UD), and Overdrive Clutch (OD).

Although the 45RFE is considered a 4 speed transmission, it really has 5 forward gear ratios. The 545RFE is considered a 5 speed transmission, but it really has 6 forward gear ratios. 2nd gear (1.67:1) and 2nd prime (1.50:1) gear are so close in ratio that they are not considered to be different gear ratios, although both are used as 2nd gear under certain conditions. During most upshift and downshift maneuvers, 2nd gear will be used. 2nd prime gear is only used for a high speed 4-2 downshift. The 545RFE transmission is essentially a software change to the TCM that allows an additional overdrive ratio of (0.667:1). The gear ratio of 4th Prime is achieved by applying the 2C and OD clutches. The 4th Prime is used above 52 mph. All gear ratios in the 45RFE/545RFE are achieved by applying two elements (clutches). During a shift, one element is released and another is applied, resulting in a different ratio. This is called a clutch to clutch shift. In order to perform a 4-2 downshift, two elements would have to be released and two different elements applied. The 2nd prime gear ratio allows a clutch to clutch 4-2' (2nd prime) downshift.

The oil pump in the 45RFE/545RFE is a dual stage positive displacement gear type pump. At idle and low engine speeds, both stages are working. Once the engine speed reaches a point where one side of the pump can supply the necessary system requirements, the second stage is vented. This pump configuration gives the pressure and flow of a large displacement pump at low speeds, and the economy of a small displacement pump at higher engine speeds. The oil pump housing also contains some of the valves that are found in the valve body in a 41TE or 42LE transmission. The Converter Clutch Switch Valve, Converter Clutch Regulator Valve, Torque Converter Limit Valve, and the Pressure Regulator Valve, are all found in the oil pump housing.

The electronic control system consists of a Transmission Control Module (TCM), a Transmission Range Sensor (TRS), an Input Speed Sensor (ISS), an Output Speed Sensor (OSS), a Line Pressure Sensor (LPS), a Transmission Temperature Sensor (TTS), five pressure switches, and seven solenoids. Each clutch pack has a corresponding solenoid and pressure switch except for the reverse clutch which is controlled by the manual valve. The other two solenoids are called the Multi Select (MS) solenoid and the Pressure Control Solenoid (PCS).

The PCS is used to control line pressure. The 45RFE/54RFE controls line pressure based on inputs to the TCM. The line pressure is torque based (line pressure increases with torque) most of the time, however it is set to a predetermined value just prior to a shift and reverts back to torque based after the shift.

The MS solenoid is used to control the LR clutch during P-R and N-R garage shifts and to control the OD clutch when the Manual Valve is in the -D" position as reported by the TRS. If the manual valve is slightly out of position, the TRS will indicate a temporary zone (T3 or T4) In this case the OD clutch will be controlled by the OD solenoid. Note that if the TRS indicates a temporary zone, this is a valid PRNDL code and will not set a DTC P0706(28). If the PRNDL code consistently indicates a temporary zone while the shift lever is in the "D" position, this would indicate some sort of mechanical problem in the shift linkage as opposed to an electrical TRS problem. Note: vehicle operation in the T3 temporary zone can set a DTC P1715(65).

233 / 244 ELECTRONIC TRANSFER CASE
The 233/244 Electronic Transfer Case is a conventional transfer case that uses a shift motor to place the transfer case into the desired range. A multi-position switch selector is located on the dash panel in place of a manual shift lever located on the floor.

The 233/244 Electronic Transfer Case can be identified by the Transfer Case Identification Tag, confirming the presence of a Shift Motor or the Selector Switch on the dash panel.

The Transfer Case shift motor is a bi-directional, 2-wire motor. When the motor is energized, one of the leads is 12volts and the other is ground. Reversing the polarity of the motor changes the direction of the rotation of the motor. The motor has a low speed, high torque output.

The Transfer Case Mode Sensor consists of a magnetic ring and four Hall Effect transistors that convert the shaft position into a coded signal sent to the TCCM. The magnet forces the output of the Hall device low when it is passed over it. The Mode Sensor is supplied 5 volts and a ground from the TCCM and has four output lines that feed back to the TCCM.

The Transfer Case Selector Switch is a multiposition, multi resistance switch that tells the TCCM what range is commanded. The switch assembly also contains a separate Neutral Button and four indicators, one for each selectable range.