ATF Leak Diagnosis - General Information

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

First, make sure the leak is correctly identified. Do not confuse ATF with engine oil or brake fluid (transmission fluid is usually dark red in color).

To locate the leak source, drive the vehicle a short distance (several kilometers), then park it over a clean sheet of cardboard. After a few minutes, the leak source can be identified by fluid drops on the cardboard.

Carefully inspect the suspected area and the surrounding surfaces, paying particular attention to the joints of mating gasket surfaces. Use a small inspection mirror to improve visibility.

If the leak source still cannot be identified, thoroughly wipe the suspected area with a solvent-moistened rag, then dry it.

Perform another short drive, this time frequently changing vehicle speed, then inspect the cleaned suspected area again.

Once the leak source is identified, determine and eliminate the cause of the leak before performing the repair. Replacing a damaged gasket will not produce the desired result if the defect in the mating surface that caused the gasket failure is left uncorrected. For example, a deformed flange must be straightened.

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 listed requirements cannot be met without special equipment. In this case, the vehicle should be taken to a service station.

Leaks at Mating Surfaces
Periodically inspect the cover on the right side of the transaxle case. Check that all mounting bolts are in place and properly tightened, and make sure the cover shows no signs of mechanical damage.

Possible causes of cover leaks include overtightened mounting bolts, damage to the mating surface of the transaxle case, a damaged gasket, or cracks or porosity in the case walls. If the cover or case joint is formed by a bead of sealant, the wrong type of sealant may have been used.
Leaks at Seals and Gaskets
The most common causes of transaxle seal failure include an excessively high ATF level, a blocked breather vent, mechanical damage to the seal bore walls, damage to the seal itself, or incorrect seal installation. Damage to the journal of the shaft passing through the seal, or excessive shaft play caused by bearing wear, is also possible.

Check the condition and correct seating of the dipstick tube seal. Periodically inspect the area around the speedometer drive gear or vehicle speed sensor (VSS) for signs of leakage. Replace the O-ring if necessary.
Leaks Through Defects in the Transaxle Case Walls
ATF leaks may be caused by cracks or porosity in the transaxle case body. Consult an automotive service specialist.
Check the fittings connecting the ATF cooler hoses for leaks.
Leaks at the Breather and Filler Neck
Leaks at the breather or filler neck may result from overfilling the transaxle, contamination of the ATF with coolant, or a blocked breather or return passages.