Torque Converter Forensics Honda 740 Codes

Many converter shops have reported having Honda converters returned to their shops because of 740 codes. In most cases, the remedy was to install a new O.E.M. converter. This confirmed that the code problem was due to an internal converter issue and not due to any valve body or other nonconverter related problems. Finding the cause of the 740 codes became a priority and a Root Cause Analysis (RCA) began. The first step of the RCA was to collect as many reportedly “failed” units as possible. There were many returned units available, but at first, there was no proven method for determining which converters were actually good and which were bad. The traditional method used by most transmission shops is to test the holding power of the clutch (foot/lbs of torque) with 40 psi of air over ATF applied to the piston, to create the clamping force. When the “failed” units were tested with this method, they all tested good. A better test method appeared to be in order. An equal number of known good converters were collected and another series of tests were performed on the combined samples. This time, each unit was tested by applying varying amounts air pressure/clamping force. The pressure used for the test varied from 10 psi to 40 psi and was stepped up in 5 psi increments. When the tests were completed, there was a clear division in the 20 to 25 psi range that separated the good converters from the converters that had set a 740 code. Converters that previously tested good at 40 psi were now failing in the lower pressure range.

To read the rest of this Technical Article on the Sonnax Website click here.

Article No.: TCTIP-02-10
Author: Ed Lee
Total Pages: 3

©2010 Sonnax Industries, Inc.