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Automatic Transmission Service Group
Technical Service Information
FORD AXODE/AX4S/AX4N
GEAR RATIO ERRORS
COMPLAINT:
CAUSE:
CORRECTION:
NOTE:
After overhaul, during the road test, the Malfunction Indicator Lamp (MIL) begins to flash and
the system faults to Failure Mode Effects Management (FMEM). When code retrieval is
completed, code 628 for TCC slippage, code PO741 for TCC Stuck Off or code P1744 for a TCC
Performance fault may be stored. After diagnosis of the TCC system is performed, no faults are
found. When these codes are cleared, they return on the next road test.
These complaints can be caused by installing the incorrect drive and/or driven sprockets (Refer
to Figure 1) or by installing an exchange unit that has the incorrect sprocket tooth count. It is the
sprocket tooth count that determines the target gear ratio that the PCM should see. Because the
PCM is comparing the engine rpm signal to turbine speed sensor (TSS), the PCM assumes the
converter clutch is slipping and stores the above codes due to an incorrect gear ratio caused by
the incorrect sprocket tooth count.
Use the charts in figures 2 and 3 to insure that the sprocket tooth count matches the vehicle
application. It is also a good practice to tag exchange units so that the sprocket tooth count is
known to insure that the correct transmission for that vehicle is installed.
To help diagnose this problem, raise the front wheels off the ground and see if these codes reset
with no load on the vehicle. If they do reset, the chances are that it is a gear ratio error and NOT
converter clutch slip.
DRIVEN
SPROCKET
DRIVE
SPROCKET
Figure 1
