Force motor current

[87gmc]

What exactly does Force motor current do on the trans pressure? I noticed my friends car has a hypertech tune and for firmer shift it adjusted the force motor current. Why also do 99-00 have a negative and positive one where as the 01-02 only have a force motor current.

[joecar]

As force motor current decreases (toward 0.0 A), the line pressure goes up.
The "force motor" is also called (in more recent times) the "Pressure Control Solenoid".

Minimum line pressure: PCS current is 1.1 A.
Maximum line pressure: PCS current is 0.0 A.

So, if something goes wrong (PCS signal wire breaks), the line pressure will go to maximum so the trans can protect itself.

Maximum line pressure is set mechanically by a screw adjustment in the back of the PCS.

I've never heard of negative PCS current...
the PCS current is the RMS (root-mean-square) current produced by the PWM (pulse-width-modulated) square wave voltage that the PCM drives on the PCS signal wire, so it can never be physically negative... ...eh... maybe I missed the meaning of your last sentence...???

[87gmc]

open a bin file of a 99-00 in efilive tune and you will see a pos and neg force motor control

[joecar]

87gmc,
I don't doubt you, I just find it quite strange (I don't know how to interpret it)...
I don't have a 99-00, can you post a screenshot of it...
Joe

[Blacky]

Some operating systems use a single pressure to current table. And therefor only display a single table.

Some operating systems use two pressure to current tables. One for when the pressure is increasing (positive), one for when the pressure is decreasing (negative). And therefor display two tables.

Paul