Automatic Transmission - 5L40-E/5L50-E - Introduction & Repair Instructions: Overview Cadillac STS I

Automatic Transmission Schematic Icons

Automatic Transmission Schematic Icons Icon Icon Definition NOTE: The OBD II symbol is used on the circuit diagrams in order to alert the technician that the circuit is essential for proper OBD II emission control circuit operation. Any circuit which fails and causes the malfunction indicator lamp (MIL) to turn ON, or causes emissions-related component damage, is identified as an OBD II circuit. IMPORTANT: Twisted-pair wires provide an effective "shield" that helps protect sensitive electronic components from electrical interference. If the wires were covered with shielding, install new shielding. In order to prevent electrical interference from degrading the performance of the connected components, you must maintain the proper specification when making any repairs to the twisted-pair wires shown : The wires must be twisted a minimum of 9 turns per 31 cm (12 in) as measured anywhere along the length of the wires The outside diameter of the twisted wires must not exceed 6.0 mm

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Transmission General Description (5L40-E/5L50-E)

The Hydra-matic 5L40-E is a fully automatic, five speed, rear wheel drive, electronically controlled transmission. It consists primarily of a four-element torque converter, one planetary gear set, friction and mechanical clutches and a hydraulic pressurization and control system.

The TCM commands shift solenoids, within the transmission, on and off to control shift timing. The TCM controls shift feel through the pressure control solenoid. The TCM also controls the apply and release of the torque converter clutch which allows the engine to deliver the maximum fuel efficiency without sacrificing vehicle performance. The hydraulic system primarily consists of a vane type pump, two control valve bodies, two channel plates, converter housing and case. The pump maintains the working pressures needed to stroke the clutch pistons that apply or release the friction components. These friction components, when applied or released, support the automatic shifting qualities of the transmission. The friction components used in this transmission consist of nine multiple disc clutches. The multiple disc clutches combine with four mechanical sprag clutches, to deliver six different gear ratios through the gear set. The gear set then transfers torque through the output shaft.

The transmission can be operated in any one of the seven different modes.

1. P - Park position enables the engine to be started while preventing the vehicle from rolling either forward or backward. For safety reasons, the vehicle parking brake should be used in addition to the transmission Park position. Since the output shaft is mechanically locked to the case through the parking pawl and rear internal gear, Park position should not be selected until the vehicle has come to a complete stop.
2. R - Reverse enables the vehicle to be operated in a rearward direction.
3. N - Neutral position enables the engine to start and operate without driving the vehicle. If necessary, this position should be selected to restart the engine while the vehicle is moving.
4. OD - Overdrive range should be used for all normal driving conditions for maximum efficiency and fuel economy. Overdrive range allows the transmission to operate in each of the five forward gear ratios. Downshifts to a lower gear, or higher gear ratio are available for safe passing by depressing the accelerator or by manually selecting a lower gear with the shift selector.
5. 4 - Manual Fourth can be used for conditions where it may be desirable to use only four gear ratios. These conditions include towing a trailer and driving on hilly terrain as described above. This range is also helpful for engine braking when descending slight grades. Upshifts and downshifts are the same as in Overdrive range for first, second, third and fourth gears except that the transmission will not shift into fifth gear. Manual Fourth can be selected at any vehicle speed but will downshift into fourth gear only if vehicle speed is low enough not to overrev the engine, calibratable in TCM.
6. 3 - Manual Third adds more performance for congested traffic and hilly terrain. It has the same starting ratio, first gear, as Manual Fourth but prevents the transmission from shifting above Third gear. Thus, Manual Third can be used to retain third gear for acceleration and engine braking as desired. Manual Third can be selected at any vehicle speed but will downshift into third gear only if vehicle speed is low enough not to overrev the engine, calibratable in TCM.
7. 2 - Manual Second adds more performance for congested traffic and hilly terrain. It has the same starting ratio, first gear, as Manual Third but prevents the transmission from shifting above second gear. Thus, Manual Second can be used to retain second gear for acceleration and engine braking as desired. Manual Second can be selected at any vehicle speed but will downshift into second gear only if vehicle speed is low enough not to overrev the engine, calibratable in TCM.

When the vehicle speed slows down to a speed low enough not to overrev the engine, calibratable in TCM, the transmission will automatically downshift into first gear. This is particularly beneficial for maintaining maximum engine braking when descending steep grades.

Transmission Component and System Description

The mechanical components of the 5L40/5L50-E are as follows

1. A torque converter with an electronically controlled capacity clutch (ECCC) This transmission is equipped with an electronically controlled capacity clutch (ECCC). The pressure plate does not fully lock to the torque converter cover. Instead, the pressure plate maintains a small amount of slippage, about 20 RPM, in SECOND, THIRD and FOURTH gears, depending on the vehicle application. ECCC was developed to reduce the possibility of noise, vibration or chuggle caused by TCC apply. Typical apply speeds are 49-52 km/h (30-32 mph) in THIRD gear and 65-73 km/h (40-45 mph) in FOURTH gear. Full lockup is available at highway speeds on some applications.
2. Direct and reverse clutch assembly
3. Forward and coast clutch assembly
4. Input sungear shaft and forward sprag clutch assembly
5. Output shaft assembly, with rear internal gear
6. Intermediate clutch sprag assembly
7. Overdrive clutch housing
8. Low clutch sprag
9. Center support
10. Input and reaction carrier
11. Fluid pump assembly
12. Control valve body and accumulator assembly

The electrical components of the 5L40/5L50-E are as follows

1. 1-2, 2-3 and 4-5 shift solenoids
2. Transmission manual shift shaft switch assembly
3. Transmission pressure control (PC) solenoid
4. TCC pulse width modulation (PWM) solenoid valve
5. Transmission fluid temperature (TFT) sensor
6. Input speed sensor (ISS)
7. Output speed sensor (OSS)

For more information, refer to Electronic Component Description (5L40-E/5L50-E) or Electronic Component Description (5L50-E) .

Limp Home Mode Description

If a major electrical system failure occurs which could affect vehicle safety or damage the transmission during normal operation, the TCM enters a default mode. In the default mode, the transmission operates in the following manner

1. The pressure control solenoid is off and the line pressure is at maximum in order to minimize clutch slippage.
2. The TCC solenoid is off. The converter clutch is disabled.
3. All three of the shift solenoids are off. The transmission will operate in fifth gear if the vehicle has successfully completed a 1-2 upshift in the current ignition cycle. If the vehicle has not completed a 1-2 upshift in the current ignition cycle, the transmission will operate in fourth gear. If the transmission is operating in fifth gear, fourth gear may be obtained if the engine is stopped briefly and re-started.

In default mode, the gear selector lever is ineffective at selecting forward gear ranges. In fourth or fifth gear, heat builds up in the transmission quickly, particularly in stop and go traffic. Excessive heat build-up may cause transmission failure if the vehicle is driven for extended distances in default mode.