- poor engine adjustment;
- poor gearbox adjustment;
- malfunctions in the hydraulic system of the gearbox;
- malfunctions in the mechanical gearbox system;
- malfunctions in the computer or its electrical circuit.
First of all, check the level and condition of the oil in the gearbox and the adjustment of the rods, and on models before 2001, the adjustment of the throttle control rod.
Preliminary control
Take a short drive to warm up the transmission.
Check the transmission fluid level in the gearbox.
If the fluid level is below the required level, add fluid to the transmission and check for external fluid leaks.
If the fluid level is significantly higher than required, drain the excess fluid and check to see if it contains coolant. The presence of coolant in the transmission fluid indicates that the internal walls of the radiator, which separate the transmission and coolant fluids, have been damaged.
If the transmission fluid is foamy, drain it and fill it with fresh fluid.
Check the engine idle speed. If the engine runs rough, adjust the engine before performing further checks.
Check the accelerator cable for freedom of movement and adjust if necessary.
Check the operation of the gear selection mechanism.
Make sure there are no leaks at the gasket and sealing ring locations in the gearbox.
Caution! The smell of burnt oil is a sign of contamination with small particles due to wear of the friction linings of the automatic transmission control elements. This should alert you, as a major gearbox overhaul may be required.
Caution! If the automatic transmission fluid level is below normal, air will enter the oil pump, causing oil foam to form. This in turn will cause a decrease in the operating pressure in the control system, slippage of the friction control elements of the gearbox and a delay in gear shifting.
Caution! If the oil level is higher than normal, the rotation of the planetary gears will also cause excessive foaming, leading to the same consequences as a low oil level.
Caution! The formation of an air-oil mixture will eventually cause the oil to overheat and oxidize, which will adversely affect the operation of the valves and friction controls. In addition, foaming will cause increased oil discharge through the breather, which may be mistaken for oil leaks from the system.
Diagnosing transmission fluid leaks
The location of transmission fluid leaks can be easily identified visually. Repairs usually involve replacing gaskets, sealing rings and cuffs.
If the leak is difficult to locate, follow these steps:
- identify the liquid. First, make sure it is transmission fluid that is leaking, not engine oil or coolant. The transmission fluid is dark red in color;
- take a short drive, then park the car over a large sheet of cardboard. After a few minutes, determine the location of the leak by the drops that fall on the cardboard;
- inspect the suspected leak area, paying particular attention to the gaskets. To make searching easier in hard to reach places, use a mirror;
- if no leak is found, clean the suspected area with solvent and dry it;
- drive the transmission until it warms up, changing gears in different modes, then inspect again to determine the location of the fluid leak.
Once you have located the leak, determine and fix the cause. If a gasket is being replaced, but the mating surface on which the gasket is installed is deformed or has burrs, then replacing the gasket alone will not give a positive result. It is necessary to pre-align or clean the mating surface.