P0744 – Torque converter clutch (TCC) solenoid -circuit intermittent

Reinier

By Reinier (Contact Me)
Last Updated 2018-02-17
Automobile Repair Shop Owner

Trouble CodeFault LocationProbable Cause
P0744 Torque converter clutch (TCC) solenoid -circuit intermittent Wiring, poor connection, TCC solenoid, ECM/PCM!TCM

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What Does Code P0744 Mean?

OBD II fault code P0744 is a generic code that is defined as “Torque converter clutch (TCC) solenoid -circuit intermittent”, and is set when the PCM (Powertrain Control Module) detects an intermittent loss of continuity in the control circuit of the solenoid (or on some applications, the pair of solenoids) that controls the operation of the torque converter lockup clutch.

The purpose of the torque converter is to transmit the engines’ power to the transmission, an while torque converters that are not fitted with lockup clutches are reasonably efficient, the advent of torque converter lockup clutches has greatly enhanced torque converters’ power transmission ability.

In simple terms, a torque converter is a hollow drum that is attached to the engine, and encloses a turbine that is attached to the transmission, with no direct contact between the drum and the turbine. Both components are fitted with blades, or vanes; as the outer drum rotates, its vanes pick up transmission fluid (that is contained within the drum), that is then flung against the vanes of the turbine, causing the turbine to rotate, thereby transmitting the engine’s power to the transmission.

However, this method of power transmission necessarily results in an unavoidable loss of some of the engines’ power even in the most efficient torque converters , since it is the shear strength of the transmission fluid, and not a mechanical link, that determines how much of the engines’ power is transferred onto the transmission turbine. Put in another way, this means that since some transmission fluid is forced through the small gap between the vanes on the drum and those on the turbine as the outer drum rotates, the fluid that is lost in this way cannot contribute to the transmission of power from the engine to the transmission.

This power loss is known as “slippage”, and while it can vary greatly between applications, it always means that not all of the engines’ power is transmitted to the transmission, which in turn, means that not all of the fuel being burnt in the engine is converted into energy that reaches the driving wheels. In short, this means that automatic applications without torque converter lockup clutches are less fuel-efficient than applications that do have torque converter lockup clutches.

To address all of these issues, car manufacturers have developed mechanical clutches that lock the two halves of the torque converter together; much like a clutch in a manual application that forms a mechanical link that locks the engine and transmission together. The practical advantage of this is not only that slippage can be eliminated, which increases fuel efficiency and reduces emissions, but also that under certain conditions, slippage can be induced to both make gear shifts smoother, and to protect vulnerable transmission components against the effects of over torque conditions.

In terms of operation, a torque converter lockup clutch depends on pressurized fluid either to engage, or to disengage friction surfaces that loosely resemble clutch components found in manual applications. Pressurized fluid is supplied by the transmission pressure pump, and an electronically operated solenoid is used to direct/control/regulate the flow of pressurized fluid to and from the lockup clutch.

In a fully functional system, the lockup clutch is typically engaged when the vehicle is in motion, causing all of the engines’ power to be transmitted to the transmission since there is no clutch slippage present. When the PCM determines (based on input data from (among others) the engine speed sensor, vehicle speed sensor, and throttle position sensor(s) that a gear shift may be harsh, it may momentarily relieve some of the pressure keeping  the lockup clutch engaged to induce some slippage. This has the effect of “smoothing out” gearshifts, especially during hard acceleration, since some of the engine’s torque is now being bled off by the differential rotation of the two halves of the torque converter that was brought about by the induced slippage of the lockup clutch.

From the above, it should be obvious that for the torque converter lockup clutch to work as intended, all of the components in the system need to be in perfect working order. Thus, should the PCM detect an issue such as an intermittent loss of continuity in the lockup clutch’s’ control solenoid(s) and/or associated control circuits, it will recognize that it can no longer control the lockup clutch effectively, which very often causes severe drivability issues. When this occurs, the PCM (or other control module) will set code P0744, and may also illuminate a warning light.

Where is the P0744 sensor located?

The image above shows a typical torque converter lockup clutch control solenoid (indicated by the arrow) fitted into the valve body of a BMW transmission.

Note though that while this solenoid is located inside the transmission on many applications, there are also many transmissions on which the torque converter lockup clutch control solenoid is located outside of the transmission.

WARNING: When diagnosing this code, it is critically important to refer to the manual for the affected application to locate and identify the torque converter lockup clutch control solenoid(s) correctly, since failing to do this could result in severe, if not always fatal damage to the transmission. 

What are the common causes of code P0744 ?

Note that code P0744 rarely indicates a faulty transmission, or a general failure of mechanical components in the transmission or torque converter. However, depending on the exact nature of the electrical problem in the control circuit of the torque converter lockup clutch, this code can sometimes cause a variety of transmission and lockup clutch related codes that typically set as the result of P0744, as opposed to the additional codes having caused P0744 to set. Nonetheless, some common causes of code P0744 could include the following-

  • Damaged, burnt, shorted, disconnected, or corroded wiring and or connectors in the affected control circuit
  • Defective torque converter lockup clutch control solenoid(s), but note that in cases where a pair of solenoids control the clutch, it is always preferable to replace both solenoids to prevent a recurrence of the problem
  • Failed or failing PCM or other control module, including the TCM (Transmission Control Module). Note though that these are rare events, and the fault must therefore be sought elsewhere before any control module is replaced

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