P27AC

Code

Generic P — Powertrain

Pressure Control Solenoid F Data Incompatible

Brand: Generic

Type: P — Powertrain

Views: UK: 19 EN: 33 RU: 23

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Page language: EN

Causes

Open, shorted, or corroded wiring or connector for Solenoid F
Failed or intermittent pressure control solenoid F (coil or internal valve)
Low or contaminated transmission fluid affecting solenoid/hydraulics
Faulty transmission control module (TCM) or engine control module (ECM) software/calibration
Faulty transmission hydraulic control unit (valve body) or solenoid driver
Network/communication errors between modules (CAN bus)

Symptoms

Transmission shifts harshly, slips, or hesitates
Transmission stuck in one gear or enters limp/derate mode
Illuminated MIL/Check Engine light and stored DTC P27AC
Erratic or inconsistent line pressure behavior
Delayed engagement or abnormal shift timing

What to check

Read freeze frame and full transmission-related DTCs with a capable scan tool
Verify software/calibration level for TCM and ECM and any relevant TSBs
Visually inspect wiring harness and connector for Solenoid F for damage, corrosion, or looseness
Compare commanded solenoid state vs measured current/feedback with a scan tool (live data)
Measure solenoid coil resistance at the connector (with harness disconnected)
Check transmission fluid level and condition (contamination, burnt smell, metal particles)

Signal parameters

Solenoid coil resistance (typical): ~5–30 ohms (vehicle-specific — consult service data)
Command signal: PWM duty cycle 0–100% (controls pressure) at manufacturer-specified frequency (often 20–300 Hz)
Expected circuit voltage: battery voltage on supply pin (~12 V) and low impedance ground when activated
Commanded vs actual current: solenoid current should rise when commanded; large discrepancies indicate wiring or coil faults
CAN bus: normal operating voltages ~2.5 V idle on CAN high/low with differential signaling

Diagnostic algorithm

Retrieve and record all transmission DTCs, freeze frame, and live data (solenoid commands, line pressure, gear, throttle/pedal position).
Clear codes and perform a controlled road test while watching solenoid F command and feedback parameters to confirm code returns.
Visually inspect the solenoid F connector and wiring for damage, bending, chafing, corrosion, or water ingress. Wiggle test harness while monitoring live data to reproduce fault.
With ignition off, disconnect connector and measure solenoid coil resistance at the harness/solenoid. Compare to specification. An open or shorted coil indicates replacement.
Backprobe the connector with the ignition on and engine/TCM in run state to verify supply voltage, ground, and PWM command when activated. Observe waveform with oscilloscope if available.
If wiring and connector are good but resistance and bench supply tests show correct solenoid operation, inspect transmission fluid condition and level. Replace/filter fluid if heavily contaminated.
If hydraulic behavior is still incorrect, consider valve body/solenoid pack removal and inspection for debris or stuck valve. Clean or replace as required.
If electrical and hydraulic checks pass, check module communications and TCM/ECM programming levels. Reflash or replace the TCM per manufacturer guidance if module fault is suspected.
After repairs, clear codes and verify proper operation on a road test and recheck for recurrence.

Likely causes

Damaged wiring/poor connector connection at solenoid F
Failed solenoid coil or stuck solenoid valve
Contaminated fluid or debris in valve body preventing correct solenoid response
Intermittent module-to-module communication or TCM internal fault

Fault status

⚠️ Status

Pressure Control Solenoid F data incompatible — solenoid data or feedback does not match expected values (electrical, hydraulic, or communication fault).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours