Allante V8-273 4.5L (1991)
PCM Wiring
DESCRIPTION:
The second gear pressure switch is a normally closed switch located within the transmission. This switch is opened by second gear oil when the line
pressure is high enough to allow shifts without clutch slippage. PCM/ECM input #79 (EI79) displays the voltage status of the second gear pressure
switch input (PCM/ECM terminal C10). When the switch is closed the input will be "LO" and will switch "HI" when the vehicle is in second, third or
fourth gear with sufficient line pressure to allow 3-2 downshifts.
Transmission line pressure is regulated by the vacuum modulator in response to intake manifold vacuum. At high engine load (low vacuum) the line
pressure is high, and at low load the pressure is low. The following table indicates the normal second gear pressure status:
GEAR SELECTOR POSITION THROTTLE POSITION VACUUM EI79
P, R, N, D1
ANY ANY LO
D2, D3, D4*
FULL THROTTLE LOW HI
D2, D3, D4*
MID THROTTLE MED. LO
D2, D3, D4*
CLOSED THROTTLE HIGH LO
*Second, third or fourth gear must be applied.
NOTES ON FAULT TREE:
1.
To assure full line pressure the vacuum modulator must be disconnected. EI79 status in drive 1 (D1) position should be "LO" or there is a possible
open in the second gear pressure circuit or the switch has failed.
2.
With the vacuum modulator disconnected the status should change to "HI" as the transmission applies second gear while driving on the road test.
3.
A hydraulic or electrical fault exists within the transmission. It is recommended that a pressure test be done before opening the transmission to
check the circuits and switch.