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Home >> Jeep >> 2009 >> Commander Overland, 4WD >> Repair and Diagnosis >> Transmission >> Automatic Trans >> (Powertrain Control Module (Pcm) - Electrical Diagnostics - 545RFE Automatic Transmission) >> DTC Troubleshooting >> P0721-Output Speed Sensor Circuit Performance >> Theory Of Operation

Theory Of Operation

  1. The transmission system uses two speed sensors, one to measure input RPM and one to measure output RPM. These inputs are essential for proper transmission operation. Therefore, the integrity of this data is verified through the following checks:
    • When in gear, if the gear ratio does not compare to a known gear ratio, the corresponding in-gear trouble code is set (DTCs P0731-36 and P1736).
    • An excessive change in input or output speeds indicating signal intermittent will result in codes P0716 and/or P0721 being set.
    • If the common speed sensor ground circuit is lost, both sensor inputs will read the signal from the input speed sensor at idle in neutral. Since the input speed sensor has 60 teeth and the output speed sensor has 30 teeth, this results in a an apparent speed ratio of 1:2 and may cause the DTC P1794 to set.
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