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
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.
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
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
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.