The knock sensor is attached to the cylinder block, and sends a KNK signal to the engine ECU when engine knocking is detected. The engine ECU receives the KNK signal and retards the ignition timing to suppress the knocking. This sensor contains a piezoelectric element, which generates an AC voltage when knocking causes vibration in the cylinder block and deforms the element. The engine knock frequency is in the range of 6 to 13 kHz depending on the engine model. The proper knock sensor is used in accordance with the knocking generated by each engine. There are two types of knock sensors. As can be seen from the graph, one type generates a high voltage in a narrow vibration frequency range, and the other generates a high voltage in a wide vibration frequency range. Recently some sensors that detect open and short circuits, as shown in the illustration, have come into use. In this type of circuit, 2.5 V is constantly supplied so the KNK signal is also output with a 2.5 V base frequency. STA (Starter) Signal/NSW (Neutral Start Switch) Signal
The STA signal is used to detect whether or not the engine is cranking. The main role of the signal is to gain approval from the engine ECU to increase the fuel injection volume during cranking. As can be seen from the circuit diagram, the STA signal detects in the engine ECU the same voltage that is supplied to the starter. NSW (Neutral Start Switch) signal This signal is only used in vehicles with an automatic transaxle, and is used to detect the shift lever position. The engine ECU uses this signal to determine if the shift lever is in the Por Nposition, or other position. The NSW signal is mainly used to control the ISC system.
A/C (Air Conditioner) Signal / Electrical Load Signal and Variable Resistor
A/C (Air Conditioner) signal
The A/C signal differs depending on the vehicle model, but it detects if the magnetic clutch of the air conditioner or the air conditioner switch is ON. The A/C signal is used by the ignition timing control during idling, ISC system control, fuel cut-off, and other functions.
Electrical load signal
The electrical load signal is used to detect if the headlights, rear window defogger, or other devices are ON. As can be seen in the circuit diagram, this signal circuit has several electric load signals. Depending on the vehicle model, these are compiled together and sent to the engine ECU as a single signal, or each signal is sent individually to the engine ECU. Electric load signals are used to control the ISC system.
The variable resistor is used to change the air-fuel ratio during idling and to adjust the idling CO. The variable resistor is installed in models without an oxygen sensor or air fuel ratio sensor. When the idle mixture adjusting screw is turned to the R direction, the contact inside the resistor moves to increase the VAF terminal voltage. Conversely, when the screw is turned to the L direction, the VAF terminal voltage is decreased. When the VAF terminal voltage increases, the engine ECU slightly increases the fuel injection volume to make the air-fuel mixture a little richer.
HINTAs the vane type air flow meter has an idle mixture adjusting screw in its body, a variable resistor is not required even if there is no oxygen sensor.