Transmission Electronic Control System
Transmission Electronic Control SystemElectronic System Description
The Powertrain Control Module (PCM) and its input/output network control the following transmission operations:
^ Shift timing.
^ Line pressure (shift feel).
^ Torque converter clutch operation.
The transmission control is separate from the engine control strategy in the PCM, although some of the input signals are shared. When determining the best operating strategy for transmission operation, the PCM uses input information from certain engine-related and driver demand-related sensors and switches.
Using all of these inputs signals, the PCM can determine when the time and conditions are right for a shift, or when to apply or release the torque converter clutch. It will also determine the best line pressure needed to optimize shift feel. To accomplish this, the PCM uses output solenoids to control transmission operation.
The following provides a brief description of each of the sensors and actuators used by the powertrain control module for transmission operation.
Mass Air Flow (MAF) Sensor
The Mass Air Flow Sensor (MAF) measures the mass of air flowing into the engine. The MAF sensor output signal is used by the Powertrain Control Module (PCM) to calculate injector pulse width. For transmission strategies the MAF sensor is used to regulate Electronic Pressure Control (EPC), shift and Torque Converter Clutch (TCC) scheduling.
Throttle Position (TP) Sensor
The Throttle Position (TP) sensor is a potentiometer mounted on the throttle body. The TP sensor detects the position of the throttle plate and sends this information to the Powertrain Control Module (PCM). The TP sensor is used for shift scheduling, Electronic Pressure Control (EPC) and Torque Converter Clutch (TCC) control.
Intake Air Temperature (IAT) Sensor
The IAT sensor is installed in the air cleaner outlet tube. The IAT sensor is used in determining Electronic Pressure Control (EPC) pressures.
Powertrain Control Module (PCM)
The operation of the transmission is controlled by the Powertrain Control Module (PCM). Many input sensors provide information to the PCM. The PCM then controls actuators which determine transmission operation.
Transmission Control Switch (TCS), Transmission Control Indicator Lamp (TCIL)
The Transmission Control Switch (TCS) is a momentary control switch. When the switch is pressed, a signal Is sent to the Powertrain Control Module (PCM) to allow automatic shifts from first through fourth gears or first through third gears only. The PCM energizes the Transmission Control Indicator Lamp (TCIL) when the switch is off. The TCIL indicates OVERDRIVE cancel mode activated (lamp on) and Electronic Pressure Control (EPC) circuit shorted (lamp flashing) or monitored sensor failure.
Power Take Off (PTO) Operation
NOTE: Once the battery has been disconnected for any repairs, the vehicle will need to be driven a couple miles in order to relearn the PTO operation.
The PTO unit is only available on vehicles equipped with 6.8L engine. The PTO is an option only available if it was ordered along with the vehicle. Ford recommends the use of either a Dana or Muncie PTO units that is unique for this transmission. The PTO operates in PARK or NEUTRAL with the vehicle stationary or in REVERSE, DRIVE, or when the vehicle is moving. When PTO operation occurs in DRIVE, fourth gear is inhibited and coast braking occurs in first, second, and third gear.
PTO Electronic Operation
During PTO operation, the Powertrain Control Module (PCM) receives a 12-volt input signal from the PTO circuitry at pin 4. The PTO installer must provide this signal circuit. The PCM uses this signal to disable self diagnostics and to monitor powertrain operation during PTO usage.
The PTO installer must provide an electronic throttle kicker that increase engine speed to 1,300 rpm during PTO operation.
During PTO operation, the PCM turns ON the Coast Clutch Solenoid (CCS). This allows engine power to be transmitted through the transmission input shaft to the PTO drive gear on the coast clutch cylinder.
The PCM also operates shift solenoid SS13 in the following manner during PTO operation:
^ P, R or N: ON (OFF without PTO)
^ First gear: OFF (OFF without PTO)
^ Second gear: ON (ON without PTO)
^ Third gear : ON (ON without PTO)
PTO operation can cause transmission fluid temperature to exceed the recommend maximum limit of 121°C (250°F). The failure mode logic programmed in the PCM prevents transmission damage by disabling the PTO above this limit.
PTO Hydraulic Operation
NOTE: Once the battery has been disconnected for any repairs, the vehicle will need to be driven a couple miles in order to relearn the PTO operation.
Non-PTO versions of the transmission have a source of fluid under line pressure to the 3-4 shift valve from the manual valve (OD circuit). In PTO versions the line circuit is the source.
When the vehicle is equipped for PTO operation, the transmission has changes to the hydraulic passages for the 3-4 shift valve. This allows the coast clutch to be applied in P, R, or N during PTO operation.
Non-PTO versions of the transmission have an exhaust path for the coast clutch through the REVERSE circuit. In PTO versions, a separate exhaust path for the coast clutch exists.
Due to these hydraulic features, the upper valve body, lower valve body and separator plate of the PTO versions of the transmission are unique. Refer to the parts catalog for the correct usage.
Transmission Solenoid Body Assembly
The Powertrain Control Module (PCM) controls the transmission operation through three on/off solenoids, one Pulse Width Modulated (PWM) shift solenoid, and one variable force solenoid. These solenoids and Transmission Fluid Temperature (TFT) sensor are housed in the transmission solenoid body assembly. All are part of the transmission solenoid body and are not replaced individually.
Transmission Fluid Temperature (TFT) Sensor
The Transmission Fluid Temperature (TFT) sensor is located on the solenoid body assembly in the transmission sump. It is a temperature-sensitive device called a thermistor. The resistance value of the TFT sensor will vary with temperature change. The Powertrain Control Module (PCM) monitors voltage across the TFT sensor to determine the temperature of the transmission fluid. The PCM uses this signal to determine whether a cold start shift schedule is necessary. The cold start shift schedule lowers shift speeds to allow for the reduced performance of cold engine operation. The PCM also uses the TFT sensor input to adjust Electronic Pressure Control (EPC) pressure for temperature effects and to inhibit Torque Converter Clutch (TCC) operation during the warm-up period.
Coast Clutch Solenoid (CCS)
The Coast Clutch Solenoid (CCS) provides coast clutch control by shifting the coast clutch shift valve. The solenoid is activated by pressing the Transmission Control Switch (TCS) or by selecting the 1 or 2 range with the transmission range selector lever. In MANUAL 1 and 2, the coast clutch is controlled by the solenoid and also hydraulically as a fail-safe to ensure engine braking. In REVERSE, the coast clutch is controlled hydraulically and the solenoid is not on. On Power Take-Off (PTO) equipped vehicles, the CCS will also be on during PTO operation.
Torque Converter Clutch (TCC) Solenoid
The Torque Converter Clutch (TCC) solenoid provides torque converter clutch control by shifting the converter clutch control valve to apply or release the TCC.
Electronic Pressure Control (EPC) Solenoid
CAUTION: The Electronic Pressure Control (EPC) pressure output from the variable force solenoid is NOT adjustable. Any modification to the electronic pressure control solenoid will affect the transmission warranty.
The EPC solenoid is a variable-force solenoid. The variable-force type solenoid is an electrohydraulic actuator combining a solenoid and a regulating valve. It supplies electronic pressure control that regulates transmission line pressure and line modulator pressure. This is done by producing resisting forces to the main regulator and the line modulator circuits. These two pressures control clutch application pressures.
Shift Solenoids SSA and SSB
Shift solenoids SSA and SS13 provide gear selection of first through fourth gears by controlling the pressure to the three shift valves.
Anti-Lock Brake Speed Sensor
The programmable speedometer/odometer module (PSOM) receives input from the rear brake anti-lock sensor. After processing the signal, the PSOM relays it to the Powertrain Control Module (PCM) and the speed control module.
Turbine Shaft Speed (TSS) Sensor
The Turbine Shaft Speed (TSS) sensor is a magnetic pickup that sends the Powertrain Control Module (PCM) information on the rotation speed of the coast clutch drum. The Turbine Shaft Speed (TSS) sensor is mounted externally on the top of the transmission case. The PCM uses the TSS sensor signals to help determine Electronic Pressure Control (EPC) pressure, shift scheduling the Torque Converter Clutch (TCC) operation.
Output Shaft Speed (OSS) Sensor
The Output Shaft Speed (OSS) sensor is a magnetic pickup that provides transmission output shaft rotation speed information to the Powertrain Control Module (PCM).
The Output Shaft Speed (OSS) sensor is mounted externally on the top of the transmission extension housing. The PCM uses the OSS sensor signal to help determine Electronic Pressure Control (EPC) pressure, shift scheduling and torque converter clutch TCC operation.
Digital Transmission Range (TR) Sensor
The digital Transmission Range (TR) sensor is located on the outside of the transmission at the manual lever. The sensor completes the start circuit in PARK and NEUTRAL, the back-up lamp circuit in REVERSE an a neutral sense circuit for GEM control of 4x4 low engagement. The sensor also opens/closes a set of four switches that are monitored by the Powertrain Control Module (PCM) to determine the position of the manual lever (P, R, N, (D) , 2, 1).
Brake Pedal Position (BPP) Switch
The Brake Pedal Position (BPP) switch tells the Powertrain Control Module (PCM) when the brakes are applied. The torque converter clutch (TCC) disengages when the brakes are applied. The BPP switch closes when the brakes are applied and opens when they are released.
Electronic Ignition (EI) System
The Electronic Ignition (EI) consists of a crankshaft position sensor, two four-tower ignition coils and the Powertrain Control Module (PCM). The ignition control module operates by sending crankshaft position information from the crankshaft position sensor to the ignition control module. The ignition control module generates a profile ignition pickup (PIP) signal (engine rpm) and sends it to the PCM. The PIP signal is one of the inputs that the PCM uses to determine transmission strategy, Wide-Open Throttle (WOT) shift control, torque converter clutch control and EPC pressure.
Distributor Ignition (DI) System
The profile ignition pickup sensor sends a signal to the Powertrain Control Module (PCM) indicating the engine rpm and the crankshaft position.
Air Conditioning (A/C) Clutch
An electromagnetic clutch is energized when the clutch cycling pressure switch closes. The switch is located on the suction accumulator/drier. The closing of the switch completes the circuit to the clutch and draws it into engagement with the compressor driveshaft. When the A/C clutch is engaged, Electronic Pressure Control (EPC) pressure is adjusted by the PCM to compensate for additional load on the engine.
Manifold Absolute Pressure (MAP) Sensor
The Manifold Absolute Pressure (MAP) sensor senses atmospheric pressure to produce an electrical signal. The frequency of this signal varies with intake manifold pressure. The Powertrain Control Module (PCM) monitors this signal to determine altitude. The PCM then adjusts the transmission shift schedule and EPC pressure for altitude. On diesel engines, the MAP sensor measures boost pressure. The PCM monitors this signal and adjusts EPC pressure.