* Transmission Control Module (TCM) Failure: The TCM is the "brain" of the transmission. A malfunctioning TCM can fail to properly command the torque converter clutch (TCC) to unlock at lower speeds. This is a very common culprit. A faulty TCM might be sending a constant "locked" signal.
* Torque Converter Clutch Solenoid Failure: This solenoid is responsible for engaging and disengaging the TCC. If it's stuck or failing, it could keep the converter locked. This is often a less expensive fix than a TCM replacement.
* Faulty Wiring or Connectors: Problems in the wiring harness between the TCM and the solenoid, or a corroded connector, could prevent the correct signals from being sent or received.
* Internal Transmission Problems: While less likely to cause *constant* lockup, severe internal transmission damage (worn clutches, low fluid, etc.) could lead to the TCC remaining engaged. The transmission may be trying to compensate for the damage by keeping the torque converter locked.
* Low Transmission Fluid: Low fluid level can cause various transmission problems, including improper TCC operation. Check the fluid level and condition – it should be pink and smell clean, not brown and burnt.
* Torque Converter Failure: Although less common as the sole cause of *always* locked, a faulty torque converter itself could contribute. A mechanically seized torque converter will prevent unlocking.
Why is this a problem?
A locked torque converter at all speeds prevents the transmission from smoothly shifting gears and effectively managing engine speed. This leads to:
* Reduced Fuel Economy: The engine is always directly coupled to the wheels, even at low speeds, leading to higher RPMs and increased fuel consumption.
* Increased Wear and Tear: The transmission and engine experience increased stress, leading to premature wear.
* Overheating: The transmission will overheat due to the constant stress and lack of proper cooling from the torque converter's normal operation.
* Transmission Damage: Continued operation in this condition will likely cause catastrophic transmission failure.
What to do:
1. Check Transmission Fluid: This is the easiest and cheapest first step. Check the level and condition. If low or burnt, have it addressed immediately.
2. Have a Professional Diagnose: This is crucial. A mechanic with diagnostic equipment can check the TCM, solenoids, wiring, and other components to pinpoint the exact cause. Avoid simply replacing parts without a proper diagnosis as this can be costly and ineffective.
Ignoring this issue will almost certainly lead to significant and expensive transmission repairs, potentially requiring a complete rebuild or replacement. Get it checked out as soon as possible.
