Honda Civic. Manual — part 173

Fig. 27: Grade Logic Control - Ascending Control Graph
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Grade Logic Control: Descending Control

When the PCM determines that the vehicle is going down a hill in D, the shift-up
speed from 4th to 5th gear, 3rd to 4th gear, and from 2nd to 3rd (when the throttle is
closed) becomes faster than the set speed for flat road driving to extend the 4th
gear, 3rd gear, and 2nd gear engagement areas. This, in combination with engine
braking from the deceleration lock-up, achieves smooth driving when the vehicle is
descending. There are three descending modes with different 4th gear driving areas,
3rd gear driving areas and 2nd gear driving areas according to the magnitude of a
gradient stored in the PCM. When the vehicle is in 5th or 4th gear and you are
decelerating while applying the brakes on a steep hill, the transmission will
downshift to a lower gear. When you accelerate, the transmission will then return to
a higher gear.

Fig. 28: Grade Logic Control - Descending Control Graph

2008 Honda Civic LX

2006-08 TRANSMISSION Automatic Transmission - Civic (Except Hybrid)

Courtesy of AMERICAN HONDA MOTOR CO., INC.

Clutch Pressure Control

The PCM actuates A/T clutch pressure control solenoid valves A, B, and C to
control the clutch pressure. When shifting between gears, the clutch pressure
regulated by A/T clutch pressure control solenoid valves A, B, and C engages and
disengages the clutch smoothly.

The PCM receives input signals from the various sensors and switches, processes
data, and outputs current to A/T clutch pressure control solenoid valves A, B, and
C.

Fig. 29: Clutch Pressure Control System Diagram
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Lock-up Control

2008 Honda Civic LX

2006-08 TRANSMISSION Automatic Transmission - Civic (Except Hybrid)

Shift solenoid valve D controls the hydraulic pressure to switch the lock-up shift
valve and lock-up ON and OFF. The PCM actuates shift solenoid valve D and A/T
clutch pressure control solenoid valve A to start lock-up. A/T clutch pressure
control solenoid valve A applies and regulates hydraulic pressure to the lock-up
control valve to control the volume of the lock-up. The lock-up mechanism operates
in D (1st, 2nd, 3rd, 4th, and 5th gears) and in D3 (1st, 2nd, and 3rd gears).

Fig. 30: Lock-Up Control System Diagram
Courtesy of AMERICAN HONDA MOTOR CO., INC.

PCM A/T Control System Electrical Connections

2008 Honda Civic LX

2006-08 TRANSMISSION Automatic Transmission - Civic (Except Hybrid)

Fig. 31: PCM A/T Control System - Circuit Diagram
Courtesy of AMERICAN HONDA MOTOR CO., INC.

PCM A/T Control System Inputs and Outputs

2008 Honda Civic LX

2006-08 TRANSMISSION Automatic Transmission - Civic (Except Hybrid)