Located in this section is a description of the Engine Fuel and Emission Control System (ECCS) for the 1992-1994 Nissan VE30DE engine found in the 92-94 Maxima SE models. This information is graciously borrowed from the Nissan Factory Service Manual and is intended for reference purposes only. Using this section will allow you to better understand what each sensor, control and valve does and how they all tie together.

Engine Control Module (ECM)

The ECM is the heart of the ECCS and is very much the brain of the entire system. It is located behind the stereo system in the center console (located on the floor). It is accessible without removing any major interior panels from either passenger foot well.

Crankshaft Position Sensor

This is a major component of the ECCS. It monitors engine speed and piston position, and sends signals to the ECM to control fuel injection, ignition timing and other functions. It’s an intricate unit consisting of a rotor plate and LED’s which pass through small slits in the rotor plate. Slits are cut out every 1 degree on the outside and every 120 degrees on the inside. The LED passes through these slits and forms rough-shaped pulses which are converted into on-off pulses by the wave forming circuit, which are sent to the ECM.

Mass Air Flow Sensor (MAF)

This measures intake airflow by maintaining the temperature of a hot film placed in the air stream. The amount of heat dissipated from the film depends on the volume of the airflow around the film. Thus, the higher the airflow, the more heat is dissipated and a higher current is needed to maintain the film temperature. The ECM monitors this current and calculates the airflow rate.

Engine Coolant Temperature Sensor

This sensor detects engine coolant temperature via a thermistor which is sensitive to the change in temperature. Electrical resistance of the thermistor decreases in response to the temperature rise.

Throttle Position Sensor

This unit actually consists of two switches (hence the two harness connections). The first is the “soft closed TPS” and is the main sensor. It is directly attached to the throttle plate and acts as a potentiometer as the throttle is moved. This means that it’ll create a higher voltage the more the throttle plate is opened. When closed, it’ll measure 0 volts. It also detects the speed at which the throttle is opened or closed.

The “hard closed TPS” is a backup system which works when the “soft closed TPS” system is malfunctioning. All this system does is bridge a connection between two elements when the throttle is fully closed, thus sending a signal to the ECM. When the throttle is opened, the signal disappears.

Fuel Injector

The fuel injector is a small, elaborate solenoid valve. As the ECM sends injection signals to the injector, the coil in the injector pulls the needle valve back and fuel is released into the intake manifold through the nozzle.

Fuel Pressure Regulator

This unit maintains the fuel pressure at 43.3psi through a spring-loaded valve. As intake manifold vacuum increases, it pulls on the spring to allow more fuel to return from the injectors to the fuel tank.

Heated Oxygen Sensor

This is located in the exhaust downpipe (y-pipe) and monitors the oxygen level in the exhaust gasses. The sensor is made of ceramic titania, the electric resistance of which drastically changes at the ideal air-fuel ratio. The ECM supplies the sensor with approximately 1 volt and then measures the output voltage depending on its resistance. The heater is used to activate the sensor element quicker.

Fuel Pump

This is a turbine type design which is located in the fuel tank. Do not run the fuel pump without having fuel in the lines (i.e., don’t run out of gas!). The fuel pump will run for 5 seconds when you place the ignition key to ‘ON’ but don’t start the engine.

Power Transistor Unit & Ignition Coils

The ignition signal from the ECM is amplified by the power transistor and fires the specific ignition coil by turning that coil’s circuit on and off.

Idle Air Control Valve (IACV)-Air Regulator

This provides an air by-pass when the engine is cold for a fast idle during warm-up. Wax, a piston and a spring are located in the valve. When the coolant temp is low, the valve allows air to pass through. As the coolant temp rises, the wax expands to shut off the air by-pass, which decreases idle speed down to normal.

Idle Air Adjusting Unit (IAA)

This entire unit consists of the IACV-AAC valve, IACV-FICD solenoid valve, IACV-air regulator and idle adjusting screw. It is one unit and should not be disassembled.

Idle Air Control Valve (IACV)-Auxiliary Air Control (AAC) Valve

The ECM actuates the IACV-AAC by an on/off pulse. When the ECM transmits an on pulse, the valve opens to let more air into the intake, thus increasing idle speed.

Idle Air Control Valve (IACV)-Fast Idle Control Device (FICD) Solenoid Valve

All this does is bump up the airflow a bit when the air conditioner is turned on.

Vehicle Speed Sensor

This sensor provides a speed signal to the ECM. It is a reed switch, which means it is a magnet spinning near a magnetic switch. As one side of the spinning magnet passes the switch, it momentarily opens it. The faster the speed, the faster the switch is opening and closing and the higher the speed registered on the speedometer.

Power Steering Oil Pressure Switch

This senses when the wheel is being turned (thus loading the engine through the power steering pump) and sends a signal to the ECM which transmits a signal to the IACV-AAC valve to bump up the airflow.

Knock Sensor (KS)

This is attached to the cylinder block and senses engine knocking through a piezoelectric element. A knock is transmitted as vibrational pressure through the sensor which is then converted into a voltage signal processed by the ECM

Valve Timing Control (VTC) Solenoid Valve

One valves is installed on one cylinder head (two valves total). This valve takes a signal from the ECM and controls oil pressure to the VTC sprockets. This then regulates the position of the intake camshafts.

Exhaust Gas Recirculation (EGR) Valve

This controls the quantity of exhaust gas to be fed into the intake manifold through a vacuum actuated taper valve. This vacuum is applied in response to the opening of the throttle valve.

EGR Control (EGRC)-Solenoid Valve

The solenoid valve responds to an on/off signal from the ECM. When it’s off, a vacuum signal from the throttle body is fed into the EGR valve. When the signal is on, an electric plunger shuts off the vacuum to turn off the EGR valve.

EGR Temperature Sensor (California Model Only)

This monitors the exhaust gas temperature and transmits a signal to the ECM. It works the same way as the coolant temperature sensor through the use of a thermistor. Electric resistance of the thermistor decreases in response to a ride in temperature.

Power Valve (Manual Transmission Models Only)

This valve controls the suction passage of the power valve control system. It is either set fully closed or fully opened by the power valve actuator operated by the vacuum stored in the surge tank. The vacuum in the surge tank is controlled by the power valve control solenoid valve.

Power Valve Control Solenoid Valve (M/T Models Only)

Works the same as the EGRC solenoid valve. ECM sends either an on or off signal which either allows vacuum to pass or shuts it off.

Data Link Connector for CONSULT

This is located behind the fuse box cover in the interior and is used to hook up your ECCS to a Nissan CONSULT system which is normally only found at Nissan dealers.

Activated Carbon Canister

This is filled with active charcoal to absorb evaporative gases produced in the fuel tank. These absorbed gases are then sucked into the intake manifold by vacuum for combustion.