Electronically-Controlled Automatic Transmissions – Quick Study Notes

Transitioned from hydraulic to electronic control; mechanical internals largely unchanged.
Electronics replace hydraulic governors, modulators, springs for shift timing & line pressure.

Central logic unit processes sensor inputs & commands solenoid outputs.
Shares data over network if engine & transmission have separate modules.
Features adaptive learning (aka TAP/CVI) to adjust pressures over time.
Stores trouble codes for electrical or performance faults; reset/relearn after repairs.

Throttle Position Sensor (TPS): higher voltage → delayed upshift, higher line pressure.
Engine Coolant Temperature (ECT): delays TCC & upshifts when cold; locks TCC & holds direct gear if hot.
Engine Speed (CKP): base for shift patterns & TCC slip check (allowed slip < 250\,\text{rpm}).
MAP / MAF: load signals → adjust shift schedule & pressure.
Ambient Air Temp: boosts pressure when intake air is cold.

Manual Lever Position / Range Switch: reports PRNDL to PCM.
Fluid Pressure Switch Assembly: verifies hydraulic state & start-in-park/neutral.
Transmission Fluid Temperature (TFT): cold → delayed shifts; hot → lock TCC & direct gear.
Input/Turbine Speed Sensor (ISS): compares with engine rpm to compute slip.
Output/Vehicle Speed Sensor (VSS): road speed, gear ratio check, default patterns if VSS fails.

Brake Switch: releases TCC, commands downshifts in tow/haul, shift-interlock.
A/C Switch, Cruise Control, Power Steering Pressure (PSPS), Accelerator Pedal Position (APP): fine-tune shift feel & pressure.

Two actuation types:
• On/Off (normally open/closed) – control shift valves & basic TCC.
• PWM – modulate pressure for EPC, TCC, clutch fill.
EPC/PCS/VFM solenoid precisely regulates main line pressure (current 0.1–1.1\,\text{A} ↔ max–min pressure).

Minimum of 2 shift solenoids; ON/OFF pattern selects gear (park/neutral/reverse bypass solenoids).
PCM rationalizes TPS, ISS, VSS, MAP/MAF, TFT data to time shifts.
Gear ratio = \dfrac{\text{ISS}}{\text{OSS}}; ratio error sets code.

Load ↑ → delayed upshift & higher line pressure.
TFT cold ↑ → temporary pressure boost.
PCM logs shift time (clutch volume index); adjusts EPC current to correct early/late shifts.
Default/Limp: solenoids off, max pressure, single forward gear + reverse.

PCM retards ignition during shifts to soften feel without reducing holding force.
Tow/Haul switch: delays upshifts, increases pressure, may downshift on braking for engine braking.

Transitioned from hydraulic to electronic control; mechanical internals largely unchanged.
Electronics replace hydraulic governors, modulators, springs for shift timing & line pressure.

Central logic unit processes sensor inputs & commands solenoid outputs.
Shares data over network if engine & transmission have separate modules.
- Data sharing often occurs via a Controller Area Network (CAN) bus, allowing high-speed, reliable communication between modules.
Features adaptive learning (aka TAP/CVI) to adjust pressures over time.
- Adaptive Relearn Scenarios: Relearn procedures are critical after transmission component replacement (e.g., solenoids, clutches) or control module flashing to establish new base shift parameters.
Stores trouble codes for electrical or performance faults; reset/relearn after repairs.
- DTC Specificity: Trouble codes distinguish between circuit faults (e.g., open, short to ground/power) and performance faults (e.g., incorrect gear ratio, excessive slip).

Throttle Position Sensor (TPS): higher voltage → delayed upshift, higher line pressure.
Engine Coolant Temperature (ECT): delays TCC & upshifts when cold; locks TCC & holds direct gear if hot.
Engine Speed (CKP): base for shift patterns & TCC slip check (allowed slip < 250\,\text{rpm}).
MAP / MAF: load signals → adjust shift schedule & pressure.
Ambient Air Temp: boosts pressure when intake air is cold.

Manual Lever Position / Range Switch: reports PRNDL to PCM.
Fluid Pressure Switch Assembly: verifies hydraulic state & start-in-park/neutral.
Transmission Fluid Temperature (TFT): cold → delayed shifts; hot → lock TCC & direct gear.
Input/Turbine Speed Sensor (ISS): compares with engine rpm to compute slip.
Output/Vehicle Speed Sensor (VSS): road speed, gear ratio check, default patterns if VSS fails.

Brake Switch: releases TCC, commands downshifts in tow/haul, shift-interlock.
A/C Switch, Cruise Control, Power Steering Pressure (PSPS), Accelerator Pedal Position (APP): fine-tune shift feel & pressure.

Two actuation types:
• On/Off (normally open/closed) – control shift valves & basic TCC.
• PWM – modulate pressure for EPC, TCC, clutch fill.
- PWM Duty Cycle: PWM solenoids achieve variable pressure by rapidly cycling on/off; the percentage of time "on" (duty cycle) determines the average pressure.
EPC/PCS/VFM solenoid precisely regulates main line pressure (current 0.1–1.1\,\text{A} ↔ max–min pressure).
Valve Body Function: The valve body houses hydraulic passages and mechanical valves, precisely directing fluid flow as commanded by the solenoids for gear changes and pressure regulation.

Minimum of 2 shift solenoids; ON/OFF pattern selects gear (park/neutral/reverse bypass solenoids).
PCM rationalizes TPS, ISS, VSS, MAP/MAF, TFT data to time shifts.
Gear ratio = \dfrac{\text{ISS}}{\text{OSS}}; ratio error sets code.

Load ↑ → delayed upshift & higher line pressure.
TFT cold ↑ → temporary pressure boost.
PCM logs shift time (clutch volume index); adjusts EPC current to correct early/late shifts.
Default/Limp: solenoids off, max pressure, single forward gear + reverse.
- Limp Mode Triggers: Limp mode is often activated in response to critical sensor failures (e.g., VSS, ISS) or severe electrical faults to prevent further damage, typically engaging a fixed high gear.

PCM retards ignition during shifts to soften feel without reducing holding force.
Tow/Haul switch: delays upshifts, increases pressure, may downshift on braking for engine braking.

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