The VLPS

Its purpose is simple, to improve fuel economy. Typically, factory predetermined line pressures in drive runs approximately 120-130 psi while reverse is usually in the range of 180-190 psi. The shift solenoids double as clutch pressure control solenoids controlling the rate in which a clutch is applied during both a garage shifts into gear and shifting from one gear to the next. Once into gear, the full predetermined line pressure is applied to the clutch. This means that at idle in drive or reverse, the engine is driving the pump through the torque converter at 120 or 180 psi. Lowering line pressure under these conditions causes the engine to not work as hard increasing fuel economy.

This is what the added line pressure control solenoid does, it lowers line pressure when it duty cycles. Characteristically, line pressure solenoids are normally applied solenoids controlling line pressure on the spring side of the pressure regulator valve. The regulated pressure this type of solenoid generally produces runs from 0 psi at 1 amp to 90 psi at 0.1 amps. The added pressure to the spring side of the pressure regulator valve is what raises line pressure. The design of the solenoid is that should it turn off, maximum line pressure will result as a failsafe strategy.

The 41TES/42RLE-VLP line pressure solenoid works entirely different. This is a normally vented solenoid. The regulated pressure this solenoid produces generally runs from 90 psi at 1 amp to 0 psi at 0.1 amps. This regulated pressure works the end of the pressure regulator valve opposite the spring. As it is energized it lowers pressure. As it turns off it restores pressure back to predetermined levels (higher pressure).

The operation of the solenoid is important to understand when it comes to diagnosing problems related to the solenoid and/or transducer.

There are six main codes assigned to this system. They are:

P0868: Line pressure low

P0869: Line pressure high

P0932: Line pressure sensor circuit

P0934: Line pressure sensor circuit low

P0945: Line pressure sensor circuit high

P1745: Transmission line pressure too high for too long

The following is detailed O. E. diagnostic information for each of these codes:

Code P0868 - Line Pressure Low

The PCM continuously monitors Actual Line Pressure (the transducer signal-LPS) and compares it to Desired Line Pressure (VLPS command). If the Actual Line Pressure is more than 10 psi below Desired Line Pressure, this DTC will set.

Possible Causes (no specific order):

Check for related DTC’s

Low Fluid Level

Transducer (LPS) 5 volts supply circuit open

Transducer (LPS) 5 volts supply circuit shorted to ground

Transducer (LPS) 5 volts supply circuit short to voltage

VLPS control circuit shorted to another circuit

Internal transmission failure

Malfunctioning Transducer (LPS)

Malfunctioning VLPS

Cracked, plugged, or mis-installed Primary Oil Filter

Stuck or Sticking Pressure Regulator Valve

Malfunctioning PCM

Theory of Operation
Line pressure is monitored by the Transducer and regulation is achieved by changing the duty cycle of the VLPS controlled by the Transmission Control System in the PCM. 5% duty cycle = solenoid OFF which equals maximum line pressure. 62% duty cycle = solenoid ON which equals minimum line pressure. The Transmission Control System calculates the desired line pressure based on inputs from both engine load and transmission.

The Transmission Control System calculates torque input to the transmission and uses it as the primary input to the desired pressure calculation. This is called Torque Based Line Pressure. In addition, the line pressure is set to a preset level 827 or 931 kPa (120 or 135 psi) during shifts and in Park and Neutral to ensure consistent shift quality. The desired line pressure is continuously being compared to the actual line pressure. If the actual line pressure is consistently lower than the target while driving, the line pressure low DTC P0868 will set.

Code P0869 - Line Pressure High
The PCM continuously monitors Actual Line Pressure (the transducer signal). If the Actual Line Pressure reading is greater than the highest Desired Line Pressure (VLPS command) ever used in the current gear, while the VLPS duty cycle is at or near maximum value (which should result in minimum line pressure), this DTC will set.

Possible Causes (no specific order):

Transducer (LPS) 5 volts supply circuit open

Transducer (LPS) 5 volts supply circuit shorted to ground

Transducer (LPS) ground circuit open

Transducer (LPS) connection faulty

Malfunctioning Transducer (LPS)

VLPS control circuit open

Transmission Control Relay Output Circuit Open

Mechanical failure of the VLPS

Stuck or Sticking Pressure Regulator Valve

Malfunctioning PCM

Theory of Operation
Line pressure is measured by the Transducer and regulation is achieved by changing the duty cycle of the VLPS controlled by the Transmission Control System in the PCM. 5% duty cycle = solenoid OFF which equals Maximum line pressure. 62% duty cycle = solenoid ON which equals minimum line pressure. The Transmission Control System calculates the desired line pressure based on inputs from both engine load and transmission.

The Transmission Control System calculates torque input to the transmission and uses it as the primary input to the desired pressure calculation. This is called Torque Based Line Pressure. In addition, the line pressure is set to a preset level 827 or 931 kPa (120 or 135 psi) during shifts and in Park and Neutral to ensure consistent shift quality. The desired line pressure is continuously being compared to the actual line pressure. If the actual line pressure is consistently higher than the highest desired line pressure ever used in the current gear, the line pressure high DTC P0869 will set.

Code P0932 - Line Pressure Sensor CircuitThe PCM continuously monitors Actual Line Pressure (the transducer signal) and compares it to the Desired Line Pressure (VLPS command). If the Actual Line Pressure reading is more than 172.4 kPa (25 psi) higher than the Desired Line Pressure, but is less than the highest Line Pressure ever used in the current gear, DTC P0932 will set.

Possible Causes (no specific order):

Check for related DTC’s

Faulty VLPS connector and wiring

Internal transmission failure

Malfunctioning PCM

Theory of Operation
Line pressure is electronically controlled by the Transmission Control System and is measured by the Transducer (Line Pressure Sensor - LPS). The desired line pressure is continuously being compared to the Actual Line Pressure and is regulated electronically changing the duty cycle of the VLPS. 5% duty cycle = solenoid OFF which equals maximum line pressure. 62% duty cycle = solenoid ON which equals minimum line pressure.

The Transmission Control System calculates the desired pressure based on inputs from the transmission and engine. A calculated torque input to the transmission is used as the primary input of the desired line pressure calculation and is called Torque Based Line Pressure. In addition, the line pressure is set to a preset level 827 to 931 kPa (120 to 135 psi) during shifts and in Park and Neutral to ensure shift quality.

Code P0934 - Line Pressure Sensor Circuit Low
The DTC will set when the monitored Transducer (Line Pressure Sensor - LPS) signal voltage is less than or equal to 0.35 volts for 0.18 seconds.

Possible Causes (no specific order):

Transducer (LPS) 5 volts supply circuit open

Transducer (LPS) 5 volts supply circuit shorted to ground

Transducer (LPS) signal circuit shorted to ground.

Malfunctioning Transducer (LPS)

Malfunctioning PCM

Theory of Operation
Line pressure is electronically controlled by the Transmission Control System and is measured by the Transducer (Line Pressure Sensor - LPS). The desired line pressure is continuously being compared to the Actual Line Pressure and is regulated electronically changing the duty cycle of the VLPS. 5% duty cycle = solenoid OFF which equals maximum line pressure. 62% duty cycle = solenoid ON which equals minimum line pressure.

The Transmission Control System calculates the desired pressure based on inputs from the transmission and engine. A calculated torque input to the transmission is used as the primary input of the desired line pressure calculation and is called Torque Based Line Pressure. In addition, the line pressure is set to a preset level 827 to 931 kPa (120 to 135 psi) during shifts and in Park and Neutral to ensure shift quality.

The monitored Transducer (LPS) signal voltage should always be between 0.35 and 4.75 volts. Any monitored voltages outside of these parameters indicate a faulty Transducer  or associated wiring and will cause either DTC P0934 or P0935 to set. 

Code P0935 - Line Pressure Sensor Circuit High
The DTC will set when the monitored Transducer (Line Pressure Sensor - LPS) signal voltage is greater than or equal to 4.75 volts for the period of 0.18 seconds.

Possible Causes (no specific order):

Transducer (LPS) sensor ground circuit open

Transducer (LPS) signal circuit shorted to power

Malfunctioning Transducer (LPS)

Malfunctioning PCM

Theory of Operation
Line pressure is electronically controlled by the Transmission Control System and is measured by the Transducer (Line Pressure Sensor - LPS). The desired line pressure is continuously being compared to the Actual Line Pressure and is regulated electronically changing the duty cycle of the VLPS. 5% duty cycle = solenoid OFF which equals maximum line pressure. 62% duty cycle = solenoid ON which equals minimum line pressure.

The Transmission Control System calculates the desired pressure based on inputs from the transmission and engine. A calculated torque input to the transmission is used as the primary input of the desired line pressure calculation and is called Torque Based Line Pressure. In addition, the line pressure is set to a preset level 827 to 931 kPa (120 to 135 psi) during shifts and in Park and Neutral to ensure shift quality.

The monitored Transducer (LPS) signal voltage should always be between 0.35 and 4.75 volts. Any monitored voltages outside of these parameters indicate a faulty Transducer  or associated wiring and will cause either DTC P0934 or P0935 to set. 

Code P1745 - transmission line pressure too high for too long
Set Condition: If the transmission has been operating in an open-loop line pressure control for 3220 kilometers (2000 miles) or 1000 2-3 upshifts.

When Monitored: Continuously with ignition on.

Possible Causes (no specific order):

Mechanical failure of the VLPS

Stuck or Sticking Pressure Regulator Valve

Transducer (LPS) sensor ground circuit open

Transducer (LPS) signal circuit shorted to power

Malfunctioning Transducer (LPS)

Theory of Operation
This DTC is an informational DTC to inform the technician that transmission has been operating in an open-loop line pressure control for 3220 kilometers (2000 miles) or 1000 2-3 upshifts resulting from a Line Pressure DTC. The 42RLE Transmission is not designed to operate in open-loop line pressure control for an extended period time. This DTC is intended to protect the transmission. If the DTC sets, the transmission controller will place the transmission into limp-in mode.

NOTE:  In order to erase this DTC you must reset (erase) the VLP Shift Counter and the Output tooth counter. This is a single procedure in the scan tool called "Clear Variable Line Pressure (VLP) counters".  If you do not erase this code the vehicle will remain in failsafe regardless of completing all necessary repairs.