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Introduction
If your check engine light is on and your OBD2 scanner reveals a P1745 code, it’s your vehicle’s way of warning you about a torque converter clutch (TCC) system problem. Specifically, P1745 indicates the TCC pressure control solenoid is stuck ON, causing the torque converter clutch to remain engaged when it shouldn’t.
This can lead to harsh shifting, stalling, overheating transmission fluid, and ultimately, serious transmission damage if left unresolved. Understanding the common causes behind this code is the first step toward accurate diagnosis and cost-effective repair.
In this guide, we’ll break down the top 5 most common P1745 causes, explain their symptoms.
Disclaimer: Causes may vary by vehicle make, model, and year. Always confirm with OEM service data before performing repairs.
1. Faulty Torque Converter Clutch Solenoid
How It Triggers P1745
The TCC solenoid controls hydraulic pressure to engage or disengage the torque converter clutch. If the solenoid sticks in the ON position due to electrical failure, debris, or wear, the clutch remains locked. This constant engagement confuses the transmission control module (TCM), setting the P1745 code.
Common Symptoms
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Rough or abrupt gear shifts
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Engine stalling at idle when coming to a stop
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Transmission overheating during extended drives
Diagnosis
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Use an OBD2 scanner with live data (e.g., CGSULIT SC530) to monitor TCC command status. If the scanner shows “TCC ON” even at idle, the solenoid may be stuck.
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Perform an electrical resistance test on the solenoid circuit according to OEM specs.
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Check transmission fluid for contaminants that could cause sticking.
2. Low or Contaminated Transmission Fluid
How It Triggers P1745
Automatic transmissions rely on clean, pressurized fluid for smooth hydraulic operation. Low fluid levels or dirty fluid clogged with clutch material can cause hydraulic sticking of the TCC solenoid.
Common Symptoms
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Slipping gears under acceleration
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Dark, burnt-smelling transmission fluid
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Overheating during highway driving
Diagnosis
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Pull the transmission dipstick (if applicable) to check fluid level and condition.
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Fluid that’s brown/black with a burnt odor needs immediate replacement.
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A fluid analysis kit can confirm the presence of metal particles or friction material.
3. Internal Transmission Wear or Damage
How It Triggers P1745
Worn clutch packs, valve body channels, or damaged hydraulic passages can cause improper TCC engagement. Internal wear increases fluid leaks inside the transmission, causing pressure loss and triggering the code.
Common Symptoms
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Delayed engagement when shifting into Drive or Reverse
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Persistent P1745 code after solenoid replacement
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Metallic debris found in transmission pan
Diagnosis
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Drop the transmission pan and inspect for excessive debris.
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Conduct a hydraulic pressure test to check for internal leaks.
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In severe cases, a full transmission rebuild may be required.
4. Faulty Transmission Control Module (TCM)
How It Triggers P1745
The TCM manages torque converter clutch operation. A software glitch or internal circuit failure can cause incorrect TCC engagement signals, leading to a stuck-on condition.
Common Symptoms
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Multiple transmission-related trouble codes along with P1745
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Erratic shifting patterns with no mechanical explanation
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No change after replacing the TCC solenoid
Diagnosis
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Use an advanced bi-directional OBD2 scanner to test TCC solenoid command function.
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Check for TCM software updates from the vehicle manufacturer.
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In rare cases, TCM replacement or reprogramming may be necessary.
5. Wiring Harness or Connector Issues
How It Triggers P1745
Damaged or corroded wiring to the TCC solenoid can short to power, causing the clutch to remain engaged continuously. Exposure to heat, road debris, and moisture accelerates harness deterioration.
Common Symptoms
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Intermittent P1745 code appearance
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Visible wire insulation damage near transmission housing
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Other unrelated electrical glitches
Diagnosis
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Perform a visual inspection of the harness from TCM to transmission.
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Use a multimeter to check continuity and shorts to power/ground.
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Repair or replace damaged connectors and wires.
Conclusion
The P1745 trouble code is most often related to TCC solenoid problems, contaminated fluid, or internal wear, but faulty electronics and wiring can also be culprits. The key to fixing it quickly—and avoiding a costly rebuild—is accurate diagnosis.
Using a reliable OBD2 scanner like the CGSULIT SC530 allows you to read codes, monitor live TCC data, and perform active tests—saving time and money before you head to a shop.
Call to Action
If you’re dealing with P1745 or other transmission trouble codes, don’t guess—diagnose.
👉 Check out the CGSULIT SC530 OBD2 Scanner for accurate, professional-grade diagnostics right in your garage.
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