P0744 Code: Torque Converter Clutch Circuit Intermittent

What the P0744 code means

The torque converter passes power through fluid, which always involves some slip. To eliminate it at cruising speed, the converter has a clutch that locks it mechanically, controlled by a solenoid.

The P0744 code is stored when that circuit fails intermittently. Compared with P0743, which flags a constant electrical fault, and with P0740, which judges performance, this code specifies that the problem comes and goes.

That produces a very recognizable symptom. When the clutch locks and releases over and over, quickly, the vehicle transmits a vibration at steady speed that many drivers describe as driving over a rumble strip, or a shake that shows up only at a certain speed and goes away when you accelerate or brake.

The causes split between electrical and hydraulic. A connector with a poor contact or a wire broken inside its insulation will cause the intermittent behavior, but so will degraded fluid whose friction properties no longer let the clutch grip steadily.

It helps to understand why this clutch exists and why its failure is so easy to feel. A torque converter passes motion through fluid, and that method always loses something along the way as slip and heat. At cruising speed that loss is pure waste, because no torque multiplication is needed. Locking the converter removes the waste and noticeably lowers fuel use, but it also makes the connection rigid: any irregularity in the lockup goes straight into the cabin, which is where the vibration comes from.

One useful tip for describing the problem. The vibration from this code is felt in a very specific speed range, typically between 60 and 90 kilometers per hour (about 37 to 56 mph) with a steady load, and it goes away as soon as you accelerate or brake. That pattern sets it apart from a wheel vibration, which grows with speed, and from a driveline vibration, which usually shows up when you accelerate. Asking exactly when it happens saves a good part of the diagnosis.

P0744 code symptoms

• Vibration at steady speed, like driving over a rumble strip.
• The shake appears at a certain speed and goes away when you accelerate or brake.
• Check engine light and transmission warning light on.
• Engine rpm that rises and falls without a gear change.
• Higher highway fuel use.
• Engine stalling when you stop, in some cases.
• Higher fluid temperature.
• The vibration appears between 60 and 90 kilometers per hour (about 37 to 56 mph) and goes away when you accelerate or brake.

Likely causes of the P0744 code

1. Degraded fluid or fluid of the wrong specification, whose friction properties no longer allow a steady lockup. A very common cause.
2. Leaking pass-through connector, which contaminates the outer harness.
3. Wire broken inside its insulation, which opens with vibration.
4. Outer connector with backed-out pins or moisture.
5. Clutch solenoid with an intermittent fault.
6. Worn torque converter clutch.
7. Valve body with internal leaks.
8. Wrong fluid level.
9. Clogged transmission filter.

How to diagnose the P0744 code step by step

1. Check the fluid level and condition. With an intermittent lockup fault, degraded fluid is the most likely cause.
2. Verify that the fluid specification is correct. A universal fluid in a transmission that calls for a specific one produces exactly this symptom.
3. Watch the lockup state in live data while cruising at a steady speed. It should stay stable, not switch back and forth.
4. Wiggle the outer harness with the engine running and look for dropouts.
5. Inspect the pass-through connector for fluid in the harness.
6. Measure the solenoid resistance while flexing the wire.
7. Check the fluid temperature during sustained driving.
8. Look for metal particles in the fluid or in the pan.
9. Ask exactly what speed range the vibration shows up in. A narrow range that disappears when you accelerate sets it apart from a wheel or driveline vibration.

How to fix the P0744 code

• Change the fluid and filter with the exact manufacturer specification. It is the repair that solves the most cases.
• Replace the pass-through connector and clean the harness if fluid leaked.
• Repair wiring with an internal break by replacing the whole section.
• Replace terminals with backed-out pins.
• Replace the clutch solenoid if its reading is unstable when you flex the wire.
• Correct the fluid level following the vehicle procedure.
• Consider replacing the converter if the clutch is worn.

With an intermittent fault, verification takes time: drive for several days at the speeds where the vibration used to appear before you call the job closed.

After the repair, confirm it by driving in the speed range where the vibration used to show up, with a steady load.

Technical reference data

• Typical clutch solenoid resistance: 10 to 30 ohms.
• With the clutch locked, engine speed drops by 150 to 400 rpm while road speed does not change.
• Lockup usually starts above 50 or 60 kilometers per hour (about 31 to 37 mph) with a steady load.
• Normal fluid temperature: 70 to 100 °C (158 to 212 °F).
• The friction properties of the fluid are specific to each transmission and are not interchangeable.
• Vibration at steady speed is the characteristic symptom of an unstable lockup.
• Converter lockup typically happens between 60 and 90 kilometers per hour (about 37 to 56 mph) with a steady load.

Brand-specific notes

The fluid is suspect number one for this code, and not only because of its condition but because of its specification. Friction properties are engineered so the clutch grips progressively and steadily. A universal fluid can meet every other requirement and fail at exactly that, which produces the characteristic vibration.

A vibration at steady speed is often mistaken for a wheel or driveline problem. The clue that sets it apart is that it shows up only in a narrow speed range and goes away when you accelerate or brake, which is when the clutch stops locking.

Frequently asked questions about P0744