Tfmprs

[L31Sleeper]

Does anyone know if the following parameter is measured pressure or commanded pressure ???

TFMPRS: Pressure Control Solenoid Pressure (kPa)

Thanx
-Justin

[joecar]

TFMPRS is the commanded "Torque Signal" pressure, see the yellow hydraulic circuit flow on this page: showpost.php?p=39472&postcount=4

Torque Signal pressure assists the pressure regulator in regulating Line Pressure (via the spring on the end of the boost valve).


There is no sensor to measure pressure.

[L31Sleeper]

So the PCM is blindly commanding ??

[joecar]

The PCM times each shift (it remembers this and the conditions)...

It compares the actual shift time with some desired shift time (for the same conditions)... [the shift time tables are involved, but they seem to me to be only a part of this... i.e. there is more to the algorithm than meets my eye...]...

It adjusts shift pressure ("torque signal") for the same shift in the future (under the same conditions) to attempt to obtain the desired shift time... [i.e. adaptive learning].

So there is an indirect feedback loop (time instead of pressure)...

For conditions/situations where this feedback cannot be applied or used, the PCM blindly commands the shift pressure table... this would be the case when the MAF is failed (i.e. SD mode).

This is my [rather poor] understanding of adaptive shift/time/pressure learning.

[L31Sleeper]

Why would it command 620kpa and read (gauge) 1300kpa ??

[joecar]

The PCS solenoid controls/regulates Torque Signal pressure which ranges ~0-620kPa (0-90psi)...

Torque Signal is applied onto the end of the boost valve and (via the isolator spring) onto the pressure regulator valve to "assist" the pressure regulator...

The pressure regulator controls/regulates Line pressure which ranges ~380-1380kPa (55-200psi)... this is what you see on a gauge connected to the Line tap on the side of the case...

The pressure regulator all by itself has a "base" pressure set by the pressure regulator spring (which pushes on the pressure regulator valve); Torque Signal pressure adds to the "base" pressure by pushing on the boost valve which pushes on the isolator spring (which also pushes on the pressure regulator valve)... i.e. Torque Signal increases the "base" pressure of the pressure regulator (which is what the PR regulates Line pressure to).

[L31Sleeper]

So what you are saying is that a Torque Signal pressure of 620kpa should equal
a line pressure of 1300kpa ?? If so how do I change it.

[joecar]

Directly: D0701-3 (during a shift).
Indirectly: D1108-10 (during a shift).

Base pressure (i.e. not during a shift): there are no known tables for this.

[L31Sleeper]

And why aren't there any tables ??

I have all the "Max Pressure Fault Enablers" turned off and I'm still
seeing 620kpa under all conditions.

Could P0748 cause this??

[joecar]

Justin,

See this: http://www.ls2.com/boggs/a4/DTC%20P0748%205.7.htm

It's telling you something is wrong with the PCS and/or the connection between it and the PCM...

Either there's an open circuit, or the PCM thinks something is wrong with that circuit and won't command it...
either way, this causes the PCS to regulate maximum Torque Signal pressure (i.e. zero current = max pressure).

P0748 is not the "cause"... but it is an indication from the PCM telling you that the PCS circuit is malfunctioning.

Log GM.TSTATE07 and GM.TSTATE08 to see what they say (they may not reveal anything new).