Frequency Solenoid Valves A & B

Fig. 38 Operating Conditions For Frequency Solenoid Valves A and B:

Frequency solenoid valve A, a part of the M-System, gets signals from the oxygen sensor through the control unit and opens air control valve A whenever the air/fuel ratio is richer than stoichiometric.
Frequency valve B, part of the X-System, gets signals from the control unit to open air control valve B when there is a rich air/fuel ratio.