REFERENCE · LIVE
A2 Solenoid Function & Test
What each solenoid does, what code it sets, and how to test it. Solenoid failure is the #1 source of P07xx codes — knowing the type and function decides whether to replace the body or just one valve.
SOLENOID TYPES
- On/Off (shift solenoid): Simple switch — controls oil flow to apply specific clutches.
- Pulse Width Modulated (PWM): Variable duty cycle controls pressure or flow proportionally.
- Variable Force Solenoid (VFS) / EPC: Current-controlled — varies line pressure with engine load.
- Linear solenoid: Proportional valve for smooth shift modulation and TCC apply ramps.
SHIFT
Shift Solenoid A / B / C / D
TypeOn/Off (older) or PWM (newer)
FunctionApply/release specific clutch packs for gear changes
Coil resistance12-30 Ω typical
Common DTCsP0750 / P0755 / P0760 / P0765
SymptomHard or no shift to specific gear; stuck in gear
TestResistance vs spec + bidirectional scan-tool actuation
PRESSURE
EPC / Line Pressure (VFS)
TypeVariable Force Solenoid (current-controlled)
FunctionModulates main line pressure based on engine load
Coil resistance4-8 Ω typical
Common DTCsP0746 / P0747 / P0748
SymptomSlipping under load, flare-shifts, harsh shifts under throttle
TestConfirm line pressure with mechanical gauge under load
CONVERTER
TCC (Torque Converter Clutch)
TypePWM (apply ramp) or On/Off
FunctionModulates lock-up clutch in the torque converter
Coil resistance20-40 Ω typical
Common DTCsP0740 / P0742 / P0743
SymptomNo lockup at cruise, shudder during TCC apply, stall when stopping
TestScan TCC duty cycle PID, verify slip RPM near zero at cruise
PRESSURE CONTROL
PCS A / B (Linear)
TypeLinear / proportional
FunctionModulates apply pressure for smooth shifts
Coil resistance5-10 Ω typical
Common DTCsP2714 / P2715 / P2723 / P2724
SymptomHarsh or flare-shift at specific gear change
TestBidirectional sweep + line pressure check during commanded shift
BAY-FLOOR RULES
Test before replace
- Pull DTCs + freeze frame — identify circuit (electrical) vs performance (mechanical/hydraulic).
- Measure coil resistance. Open/short coil = electrical replacement.
- Bidirectional actuator test. Click + line pressure response confirms it physically opens/closes.
- Confirm fluid condition. Contaminated ATF varnishes solenoid bores. Solenoid swap won\'t hold if fluid is contaminated.
- When in doubt, scan multiple PIDs. Solenoid duty + line pressure + slip RPM together tell the real story.