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Automatic transmission fluid pressure (TFP) manual valve position switch
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Automatic transmission fluid temperature (TFT) sensor
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Vehicle speed sensor assembly
For more information, refer to Electronic Component Description .
TRANSMISSION ADAPTIVE FUNCTIONS
The 4L60-E transmission utilizes a line pressure control system during upshifts to compensate for the normal
wear of transmission components. By adjusting the line pressure, the PCM can maintain acceptable
transmission shift times. This process is known as "adaptive learning" or "shift adapts" and is similar to the
closed loop fuel control system used for the engine.
In order for the PCM to perform a "shift adapt," it must first identify if an upshift is acceptable to analyze. For
example, upshifts that occur during cycling of the A/C compressor or under extreme throttle changes could
cause the PCM to incorrectly adjust line pressure. When an upshift is initiated, a number of contingencies, such
as throttle position, transmission temperature, and vehicle speed, are checked in order to determine if the actual
shift time is valid to compare to a calibrated desired shift time. If all the contingencies are met during the entire
shift, then the shift is considered valid and the adapt function may be utilized if necessary.
Once an adaptable shift is identified, the PCM compares the actual shift time to the desired shift time and
calculates the difference between them. This difference is known as the shift error. The actual shift time is
determined from the time that the PCM commands the shift to the start of the engine RPM drop initiated by the
shift. If the actual shift time is longer than the calibrated desired shift time, a soft feel or slow engagement, then
the PCM decreases current to the pressure control (PC) solenoid in order to increase line pressure for the next,
same, upshift under identical conditions. If the actual shift time is shorter than the calibrated desired shift time,
a firm engagement, then the PCM increases current to the PC solenoid in order to decrease line pressure for the
next, same, upshift under identical conditions.
The purpose of the adapt function is to automatically compensate the shift quality for the various vehicle shift
control systems. It is a continuous process that will help to maintain optimal shift quality throughout the life of
the vehicle.
Clearing Transmission Adaptive Pressure (TAP)
Transmission adaptive pressure (TAP) information is displayed and may be reset using a scan tool.
The adapt function is a feature of the PCM that either adds or subtracts line pressure from a calibrated base line
pressure in order to compensate for normal transmission wear. The TAP information is divided into 13 units,
called cells. The cells are numbered 4 through 16. Each cell represents a given torque range. TAP cell 4 is the
lowest adaptable torque range and TAP cell 16 is the highest adaptable torque range. It is normal for TAP cell
values to display zero or negative numbers. This indicates that the PCM has adjusted line pressure at or below
the calibrated base line pressure.
Updating TAP information is a learning function of the PCM designed to maintain acceptable shift times. It is
not recommended that TAP information be reset unless one of the following repairs has been made:
2004 Hummer H2
2004 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E (Introduction) - Hummer H2