AT/CVT Failure Diagnostics — General Information (Honda Civic 6)

Note: AT and CVT failures most often occur due to one of the following five reasons: reduced engine output, adjustment problems, hydraulic faults, mechanical damage, or failures of the on-board processor or its signal circuit. Diagnostics of failures should always begin with the most basic checks: assess the level and condition of the ATF (see Chapter Routine maintenance), check the adjustment of the gearshift control cables and the kick-down throttle position. Next, test drive the vehicle to determine the effectiveness of the corrections made. If the problem cannot be resolved, take the vehicle to a service station for more detailed diagnostics using special equipment. A description of some of the symptoms of AT/CVT failures is given in Diagnostics of faults in vehicle components and systems.

Primary checks

1. Warm up the transmission to normal operating temperature with a short drive.

2. Check the ATF level (see Chapter Routine maintenance):

a) If the fluid is clearly low, make the appropriate adjustment by adding the required amount of fresh ATF. Check the dipstick to make sure the adjustment is correct, then check the transmission for signs of external leaks (see below);

b) If the level is too high, drain the excess ATF, then check it for traces of coolant, indicating a leak in the internal radiator bulkheads separating its heat exchanger from the side ATF tanks (see Chapter Cooling and heating systems);



c) If the ATF is foaming, drain the transmission and fill it with fresh fluid – check the drained fluid for traces of coolant.

3. Check the engine idle speed setting.

Note: If the engine is not in good condition, do not proceed with the initial transmission checks until the appropriate corrections have been made.

4. Check the freedom of movement of the throttle control cable in kick-down mode (integra models), if necessary, make the appropriate adjustments (see Seat adjustment).

Note: The cable may function

Note: It works normally on a cold, stopped engine, which is not a guarantee of its proper operation on a running unit warmed up to normal operating temperature. Check the cable under various engine conditions.

5. Check the gear shift cable tension (see Equipment and controls in the cabin), make sure that the adjustment is correct and that it moves freely.

ATF Leak Diagnosis

1. Most leaks are easily identified by visual inspection. Repair usually consists of replacing the defective seal or gasket. If the source of the leak cannot be identified by visual inspection, proceed as described below.

2. First of all, it is necessary to exclude the possibility of an error in determining the nature of the leak. ATF should not be confused with engine oil or brake fluid (transmission fluid is usually dark red in color).

3. To identify the source of the leak, perform a short (several kilometers) drive, then park the car over a clean sheet of cardboard. After a couple of minutes, the source of the leak can be identified by traces of liquid dripping onto the cardboard.



4. Carefully inspect the suspected area and the surrounding surface, paying particular attention to the joint of the mating gasket surfaces. Use a pocket mirror to widen the viewing angle.

5. If the source of the leak still cannot be identified, thoroughly wipe the surface of the suspected area with a rag soaked in solvent, then dry it.

6. Take another short drive, this time changing speed frequently, then re-inspect the cleared suspect area.

7. After identifying the source of the leak, you should determine and eliminate the cause of its development, only then proceed to perform the necessary restoration work. Replacing the gasket will not lead to the desired result if the defect of the mating surface that led to its failure is not eliminated.

8. The following subsections list the most typical causes of ATF leaks and the conditions that must be met to prevent recurrence.

Note: Some of the above conditions cannot be met without the use of special equipment. In this case, the car should be taken to a service station.

Gasket surfaces

1. Periodically inspect the cover on the right side of the transmission housing. Check that the mounting bolts are in place and securely tightened, and make sure that there are no signs of mechanical damage on the cover.

2. Possible causes of leaks through covers include excessively tight tightening of fastening bolts, damage to the sealing surface of the transmission housing, destruction of the gasket, and the formation of cracks or porosity in the walls of the housing. If the cover or housing gasket is formed by a cushion of sealant, it is possible that the wrong type of sealant was selected.

Seals and cuffs

1. The most common causes of transmission seal failure include excessively high ATF level, obstruction of the ventilation breather, mechanical damage to the walls of the seat, damage to the seal itself, or improper installation of the latter. It is also possible that the journal of the shaft inserted into the seal is damaged, or that the latter has excessive play due to bearing wear.

2. Check the condition and correct fit of the dipstick guide tube sealing collar. Periodically inspect the area around the speedometer drive gear or speed sensor (VSS) for signs of leaks. Replace the sealing ring if necessary.

Transmission housing

1. The cause of ATF leaks may be the formation of cracks or pores in the transmission housing. Consult with car service specialists.

2. Check the tightness of the ATF cooler hose connection fittings.

Breather and filler neck

Breather or filler neck leaks can occur due to overfilling the transmission, coolant getting into the ATF, or a blocked breather or return port.

(Publication reprinted from the website: «hondabook»)