Circuit Description

The suspension control ECU opens the height control valve to lead the compressed air to the pneumatic cylinder and raise the vehicle height.

When the vehicle height is lowered, the suspension control ECU opens the height control valve to store the compressed air in the low pressure tank temporarily, and then operates the exhaust solenoid valve to release the compressed air to the outside.

Further, the height control solenoid valve (gate solenoid valve) opens and closes the passage between the right and left pneumatic cylinder.

The height control valve is on the low pressure tank and consists of 3 valves in total, leveling solenoid valve, gate solenoid valve and tank solenoid valve.

The leveling solenoid valve opens and close the passage between the compressor and the pneumatic cylinder. The gate solenoid valve opens and close the passage between the right and left pneumatic cylinder. The tank solenoid valve opens and closes the passage between pneumatic cylinder and the low pressure tank. The exhaust solenoid valve is on the compressor unit and has only one valve.

DTC

DTC No.	DTC Detecting Condition	Trouble Area
C1733/33	Either the condition 1 or 2. is detected: With the height control solenoid valve (or exhaust solenoid valve) inactivated, an open signal of the height control solenoid valve is detected for 1 sec. or more. With the height control solenoid valve (or exhaust solenoid valve) activated, a short signal of the valve is detected 8 times successively.	Gate solenoid valve Gate solenoid valve circuit Suspension control ECU
C1734/34		Leveling solenoid valve Leveling solenoid valve circuit Suspension control ECU
C1735/35		Exhaust solenoid valve Exhaust solenoid valve circuit Suspension control ECU
C1744/44		Tank solenoid valve Tank solenoid valve circuit Suspension control ECU

HINT:

Once ECU stores DTC C1733/33, C1734/34, C1735/35 or C1744/44 in the memory, the vehicle height control is suspended out until a normal signal is input to ECU from the height control solenoid valves and the exhaust solenoid valve. However, control is resumed if the ignition switch is turned OFF, then ON again.
Malfunction in the gate solenoid valve and the leveling solenoid valve:
The height control operation is suspended, and the height control indicator lamp dose not change by operating the height control switch.
Malfunction in the exhaust solenoid valve:
The vehicle height is lowered to the normal height within 30 sec., and then the height control operation is suspended. The height control indicator lamp "N" comes on or blinks, and that of "HI" and "LO" do not illuminated by operating the height control switch "UP" and "DOWN".
Abnormality of the tank solenoid valve:
Although the height control is still possible, the vehicle lowering speed may be slower.