ELECTRONIC CONCENTRATED CONTROL SYSTEM (ECCS)
The Electronic Concentrated Control System (ECCS) is a computerized emission, ignition, and fuel control system. A single Engine Control Module (ECM) uses input voltage signals received from various input components to control output.
ECM compares each input signal to the appropriate parameter preprogrammed in ECM and adjusts output voltage signals accordingly. This allows optimum vehicle performance under various conditions. On most models voltage to ECM is supplied by ECCS relay. ECCS relay has a self shut-off feature that cuts power to ECM a few seconds after ignition is turned off.
ENGINE CONTROL MODULE (ECM)
The ECM consists of a microcomputer, diagnostic mode selector, connectors and wiring for voltage signal input, voltage signal output, and power supply. The unit is not serviceable and should not be opened. The ECM contains memory and logic circuits, enabling it to interpret sensor inputs and control various engine systems. To locate ECM, see ECM LOCATIONS table.
| Application | Location |
|---|---|
| Maxima | Behind Glove Box |
ECM LOCATIONS
Note. Components are grouped into 2 categories. The first category is INPUT DEVICES, which are components that control or produce voltage signals monitored by the ECM. The second category is OUTPUT SIGNALS, which are components controlled by the ECM.
INPUT DEVICES
Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. Input signals include
A/C Switch
Informs ECM when A/C system is on. ECM responds by increasing idle speed to improve idling and reduce emissions. During heavy engine load, ECM will also open the A/C clutch relay to disengage A/C clutch.
A/C Thermo Control Amplifier
On auto A/C equipped models, informs ECM of A/C system evaporator outlet temperature. Input helps determine cooling fan operation.
Ambient Air Temperature Sensor
The ambient air temperature sensor is located in the air cleaner box. Sensor monitors temperature of incoming air. Sensor is a thermistor and increases (cold) or decreases (hot) its resistance in response to temperature changes. The air temperature sensor controls ignition timing when intake air temperature is extremely high to prevent engine knock (detonation).
Battery Voltage Compensation
Injector pulse width is directly affected by battery voltage. As battery voltage drops, so does injector pulse width, causing a lean air/fuel mixture. To compensate, ECM monitors battery voltage and increases injector pulse width if voltage drops. This monitored voltage is also used with other input values to calculate idle speed and is a factor for determining ignition timing.
Camshaft Position (CMP) Sensor
The CMP sensor detects cylinder number signal. The CMP sensor, which is mounted to front cover of engine, facing camshaft, consists of a permanent magnet, core and coil. When engine is running, gap between sensor and camshaft will periodically change. Voltage signal generated in coil is sent to ECM, which detects specific cylinder.
Crankshaft Position (CKP) Sensor
Maxima is equipped with 2 crankshaft position sensors. One CKP sensor (POS) is located at rear of engine, facing flywheel. Sensor monitors engine speed and piston position. Second CKP sensor (REF) is mounted at front of engine near oil filter. Sensor detects engine compression TDC signal.
CKP sensors consists of a permanent magnet, core and coil. When engine is running, gap between sensor and flywheel teeth (POS) or crankshaft pulley (REF) will periodically change. Voltage signal generated in coil is sent to ECM, which detects crankshaft position or compression TDC signal.
Engine Coolant Temperature (ECT) Sensor
ECT sensor is installed in the coolant inlet housing or intake manifold coolant passage. Sensor senses changes in temperature by monitoring the resistance of a thermistor. As temperature increases, thermistor resistance decreases.
Sensor sends temperature information to ECM for air/fuel mixture, timing and idle speed control. During warm-up from cold start, ECM increases fuel enrichment to maintain engine performance. As engine temperature increases, the ECM gradually decreases fuel enrichment until engine reaches normal operating temperature.
EGR Temperature Sensor
EGR temperature sensor, located near EGR valve, detects temperature of exhaust gases passing through EGR valve. Sensor has a thermistor which changes its resistance value in response to EGR flow. As temperature increases, resistance of sensor decreases. If the absence of EGR flow is detected when ECM calls for EGR operation, a low flow fault is set in ECM memory. If EGR flow is detected during no flow conditions, a high flow fault is set in ECM memory.
Fuel Temperature Sensor
Fuel temperature sensor is built into fuel rail. When fuel temperature is more than specified, ECM turns on Pressure Regulator Valve (PRV) control solenoid to increase fuel pressure.
Ignition Switch
ECM detects when ignition switch is in ON or START position. When ECM receives voltage signal for START position, it will actuate injectors and compute and initiate ignition timing sequence and other functions, including EGR control override during start-up.
Park/Neutral Position Switch (A/T Models)
Switch is located on transmission/transaxle. Switch notifies ECM when transmission/transaxle is in Park or Neutral and signals ECM of increased engine load when vehicle is in gear. This signal is used to calculate required changes in idle speed, ignition timing and injector operation.
Knock Sensor (KS)
Basic ignition timing is preprogrammed. Knock sensor detects engine knocking, converts knocking vibration into voltage signal and transmits signal to the ECM. Information is used by ECM to adjust ignition timing accordingly to eliminate detonation.
Mass Airflow Sensor
Mass airflow sensor is located in main air intake duct. The sensor uses a hot-wire type sensing element. Incoming air passing through the airflow sensor causes the hot wire to cool. As a result, ECM must apply additional current to maintain hot wire at the precalibrated temperature. The ECM measures airflow by monitoring the amount of additional current required to maintain hot wire at the precalibrated temperature.
If MAF sensor output current is outside normal operational range, a MAF sensor fault is indicated. ECM will use throttle position sensor as primary information on driving condition. During this period, ECM will limit engine speed to less than 2000 or 3000 RPM, depending on model. This will inform the driver that the vehicle is driving under fail-safe conditions and needs attention.
Neutral Switch (M/T Models)
Switch is located on transmission/transaxle. Switch notifies ECM when transmission/transaxle is in Neutral and signals ECM of increased load when vehicle is in gear. Information is used to calculate required changes in idle speed, ignition timing and injector operation.
Heated Oxygen Sensor (HO2S)
Sensor monitors the amount of oxygen in exhaust gas. Sensor provides a voltage signal which is used to adjust air/fuel mixture to obtain optimum combustion. The heater quickly brings sensor to operating temperature, reducing time engine is in open loop mode.
A rich exhaust gas mixture causes high sensor voltage (0.6-10 volt). A lean exhaust gas mixture causes low sensor voltage (0.1-0.3 volt). The ECM monitors signal from sensor and adjusts the air/fuel mixture accordingly.
Power Steering Oil Pressure Switch
Switch is attached to the power steering high pressure line. Switch monitors the power steering load and sends signal to the ECM. When oil pressure exceeds a predetermined amount, ECM sends a voltage signal to idle speed control valve to increase idle speed.
Throttle Position (TP) Sensor & Idle Switch
The TP sensor has a potentiometer which varies output voltage in response to changes in throttle position. This information is relayed to ECM in form of an input voltage signal on the 3-terminal TP sensor harness. TP sensor also has the ability to inform ECM of the rate of changes taking place in throttle plate movement. TP sensor is attached to throttle body housing and is actuated by movement of the accelerator pedal.
The idle switch is an integral part of the TP sensor. Switch is closed at idle and open during all other conditions. Switch is used to inform the ECM when the throttle is closed for fuel-cut on deceleration. Switch also has a full throttle position used only on vehicles equipped with an automatic transmission control unit.
Vehicle Speed Sensor (VSS)
Provides ECM with vehicle speed signal. VSS consists of a reed switch installed in speedometer unit. Reed switch transforms vehicle speed into pulsed signal.
OUTPUT SIGNALS
Vehicles are equipped with different combinations of ECM-controlled components. Not all components listed below are used on every vehicle. For theory and operation on each output component, refer to the indicated system.
A/C Clutch
See MISCELLANEOUS CONTROLS .
Air Assisted Injector System
See AIR ASSISTED INJECTOR SYSTEM under EMISSION SYSTEMS .
Automatic Transmission/Transaxle Control Unit (ATCU)
See TRANSMISSION/TRANSAXLE CONTROLS under MISCELLANEOUS CONTROLS.
Cooling Fan Motor
See COOLING FAN under MISCELLANEOUS CONTROLS.
Cooling Fan Relay
See COOLING FAN under MISCELLANEOUS CONTROLS.
Evaporative Emission Control System
See EVAPORATIVE EMISSION CONTROL (EVAP) SYSTEM under EMISSION SYSTEMS.
Exhaust Gas Recirculation (EGR) Control
See EXHAUST GAS RECIRCULATION (EGR) SYSTEM under EMISSION SYSTEMS.
Fuel Injector
See FUEL CONTROL under FUEL SYSTEM.
Fuel Pump Control Module (300ZX)
See FUEL DELIVERY under FUEL SYSTEM.
Fuel Pump Relay
See FUEL DELIVERY under FUEL SYSTEM.
Idle Air Control (IAC) Valve
See IDLE SPEED under FUEL SYSTEM.
IACV-Air Regulator
See IDLE SPEED under FUEL SYSTEM.
IACV-FICD
See IDLE SPEED under FUEL SYSTEM.
Idle Speed Control
See IDLE SPEED under FUEL SYSTEM.
Ignition Timing Control
See IGNITION TIMING CONTROL SYSTEM under IGNITION SYSTEM.
See MASS AIRFLOW SENSOR under INPUT DEVICES .
Power Transistor & Ignition Coil(s)
See DISTRIBUTOR IGNITION (DI) SYSTEM under IGNITION SYSTEM.
Pressure Regulator Control Solenoid
See FUEL DELIVERY under FUEL SYSTEM.
Fuel Pump
The electric in-tank fuel pump is turned on by the ECM. Fuel pump is activated when ECM supplies the missing voltage or ground signal through the fuel pump relay. Fuel pump will be energized by the ECM for up to 5 seconds when ignition is first turned on, during cranking and during running. Fuel pump will be de-energized about one second after engine stops.
Fuel Pump Control Module
When fuel pump relay is activated, battery voltage is directed through the relay to fuel pump control module and fuel pump. See FUEL PUMP RELAY. The fuel pump control module adjusts the voltage supplied to fuel pump according to engine conditions. Fuel pump control module supplies about 13 volts to fuel pump under following conditions
- One second after ignition switch is turned to ON position.
- During engine cranking.
- Thirty seconds after engine starts at temperatures greater than 122°F (50°C).
- Engine temperature is less than 50°F (10°C).
- Engine is running under heavy load condition.
Under conditions other than those listed, fuel pump control module limits fuel pump voltage to about 9.5 volts.
Fuel pump receives battery voltage through a 10-amp fuse. Ground circuit for fuel pump relay is provided through ECM. When fuel pump relay is activated, battery voltage is directed through relay to fuel pump control module and then fuel pump. See FUEL PUMP CONTROL MODULE.
Fuel Pressure Regulator
Fuel is delivered to the injector from the in-tank electric fuel pump. Fuel pressure at the injector is regulated by the fuel pressure regulator, located in the fuel return line between the injector and the fuel tank. The pressure regulator is a sealed unit divided into 2 chambers (fuel and spring) by a diaphragm. The fuel chamber receives fuel through the inlet side from the injector fuel rail. The spring chamber is connected to intake manifold vacuum.
A vacuum-operated diaphragm inside the regulator maintains fuel pressure at a specific range, taking into consideration changes in engine load. At idle, intake manifold vacuum is high, causing the diaphragm to be pulled down, allowing excessive fuel to be returned to the fuel tank. As the throttle is depressed, intake manifold vacuum decreases, allowing diaphragm regulator spring to overcome manifold vacuum, causing diaphragm to block fuel returning to fuel tank. This causes an increase in fuel pressure.
Feedback System
ECM calculates base injection pulse width by processing signals from the CMP sensor and mass airflow sensor. After receiving signals from sensors detecting engine conditions, ECM adds fuel enrichment (preprogrammed into the control unit) to the base injection width to obtain optimum fuel mixture for all operating conditions. Fuel enrichment is always available during warm-up, starting, off idle, heavy load and when engine temperature is great.
Fuel injection system incorporates mixture ratio feedback. It is designed to maintain a precise mixture ratio. Through input signals from the heated oxygen sensor, ECM can adjust air/fuel ratio to optimally control exhaust emissions and engine performance. This function takes place during closed loop operation. ECM continuously monitors itself to stay within an acceptable emissions output range. However, this feedback system can be overridden and will operate in open loop when one or more of the following conditions exist
- Starting.
- Engine and/or oxygen sensor cold.
- Driving at high speeds or under heavy load.
- Oxygen sensor monitors a too rich condition for over 10 seconds.
- Fuel shutoff solenoid is activated.
- Vehicle is decelerating.
- EGR temperature sensor is malfunctioning.
The fuel injector is a small elaborate solenoid. The ECM sends a duration signal to the injector, which in turn opens to high pressure fuel supplied by the fuel pump.
Sequential Fuel Injection (SFI)
SFI vehicles can operate in one of 2 injection modes: simultaneous or sequential. In simultaneous injection mode, fuel is injected into all cylinders at same time. In sequential injection mode, injectors are triggered in spark plug firing order. Fuel injection operates in sequential mode under most conditions. Fuel injection will shift from sequential to simultaneous mode under following conditions: when engine speed is less than 300 RPM, when engine temperature is less than 140°F (60°C), and during starting.
If mass airflow sensor malfunctions, ECM will enter fail-safe mode. In fail-safe mode, fuel injection is determined from internal default tables based on throttle position. During fail-safe mode, engine speed is limited to less than 2000 or 3000 RPM, depending on model. When the engine reaches this maximum RPM, it will not go faster, indicating the fail-safe system is in effect and vehicle needs servicing.
ECM controls engine idle speed according to engine operating conditions and component/model application. ECM will send a signal to adjust and compensate for idle speed under the following conditions: from starting to 20 seconds after start, low battery voltage, engine overheating, electrical load, A/C on, power steering load, during deceleration and when vehicle is moving at idle.
Idle speed control is achieved using various components. Models are equipped as follows
- IAC Valve, IACV-FICD, Fast Idle Cam
The ECM processes signals received from sensors to determine the optimum idle speed under varying engine conditions. The ECM senses engine condition and determines the best idle speed with regard to coolant temperature and transmission/transaxle gear position. ECM will then send an electrical on-off signal to adjust idle speed. IAC valve then regulates the amount of air bypassing throttle valve. (Scheme 1) ECM controls AAC solenoid by varying pulse width (on time).
IACV-Fast Idle Control Device (IACV-FICD)
IACV-FICD increases the idle speed for a few seconds when vehicle is first started and when A/C compressor is engaged.
Scheme 1
ELECTRONIC IGNITION (EI) SYSTEM
Electronic (direct) ignition system uses one coil per cylinder. Individual coils are plugged directly onto spark plugs. A crankshaft position (CKP) sensor located at rear of engine, facing flywheel, monitors engine speed and piston location. Signals created by the sensors are sent to the ECM for processing. ECM then delivers ignition signals to the power transistor (integral with ignition coil) to control ignition by triggering the appropriate ignition coil. Power for ignition coils is supplied from the ECM.
DISTRIBUTOR IGNITION (DI) SYSTEM
A camshaft position sensor mounted inside the distributor monitors engine speed and piston location. Signals created by camshaft position sensor are sent to the ECM.
Power transistor uses ignition signals received from ECM to trigger ignition coil. Power for ignition coil(s) is supplied through the ignition switch.
IGNITION TIMING CONTROL SYSTEM
The ignition system controls ignition timing by matching vehicle operating conditions to preprogrammed timing advance and retard specifications. These parameters are stored in the ECM memory. The ECM uses input from the camshaft and crankshaft sensors, coolant and various other sensors to determine advance requirements.
Ignition timing is controlled by the ECM according to engine operating conditions. Optimum ignition timing for various driving conditions is preprogrammed and stored in the ECM. ECM receives and processes electrical signals from various sensors to determine present driving conditions. ECM will then select optimum timing signal for the present conditions and send voltage signal to the power transistor to control timing advance and detonation retard operation (if equipped).
Ignition Timing Retard
See KNOCK SENSOR (KS) under INPUT DEVICES under COMPUTERIZED ENGINE CONTROLS.
EVAPORATIVE EMISSION CONTROL (EVAP) SYSTEM
The fuel evaporation system is used to reduce emissions of hydrocarbons (HC) into the atmosphere. The system consists of a sealed fuel tank, vacuum relief filler cap, charcoal canister, purge control valve, fuel-check valve, canister purge and vacuum signal lines, and vapor vent lines. Fuel vapor from the sealed fuel tank is stored in the activated charcoal canister when the engine is not running. Fuel vapor is retained in the canister until purged by air drawn through the bottom of the canister to the intake manifold during engine operation.
When engine is running at idle, purge control valve is closed and only a small amount of stored vapor flows into the intake manifold through the constant purge orifice. As engine speed increases and the throttle vacuum rises higher, the purge control valve opens and vapors are drawn into the intake manifold through the main purge orifice and the constant purge orifice. (Scheme 2)
EGR & EVAP Purge Control Solenoid
During prescribed operating conditions, ECM grounds EGR and EVAP solenoid to cut vacuum to EGR valve and EVAP canister purge valve. When EGR and EVAP solenoid is not activated, vacuum signal is allowed to EGR valve and EVAP canister.
Evaporative Canister
Filled with activated charcoal, canister stores fuel vapors to be burned or returned to fuel tank.
Vacuum Cut & Vacuum Cut Bypass Valves
Vacuum cut valve prevents manifold vacuum from reaching fuel tank. Vacuum cut bypass valve opens only during on-board diagnostic leak and flow checks.
Scheme 2
EGR Control
To reduce tailpipe emissions of NOx (oxides of nitrogen) and reduce engine knock, an exhaust gas recirculation (EGR) system is used. A portion of exhaust gases from the exhaust manifold is returned to the intake manifold and then the combustion chamber to dilute air/fuel mixture, therefore lowering cylinder temperature. This is controlled by the EGR valve, ECM, EGR and EVAP control solenoid valve and backpressure transducer (some models). EGR system does not operate under the following conditions
- Engine starting.
- Idle switch on.
- Low engine load.
- Low engine temperature.
- High engine temperature at high engine speeds.
Under these conditions, ECM energizes the control solenoid to pull the plunger downward, allowing control vacuum to bleed off to atmosphere. The EGR temperature sensor located near the EGR valve is used to determine when EGR is actually occurring. If sensor indicates a low exhaust gas temperature when EGR action is commanded, ECM can determine if an EGR fault is present.
EGR Backpressure Transducer (EGR-BPT)
EGR-BPT regulates the vacuum signal to EGR valve by monitoring exhaust backpressure. If excessive backpressure is detected, EGR-BPT allows EGR to function in turn lessening engine knock. If little or no exhaust backpressure is detected EGR function is reduced or cancelled. If excessive roughness is detected during off-idle operation EGR-BPT may be faulty.
During prescribed operating conditions, ECM grounds EGR and EVAP solenoid to cut vacuum to EGR valve and EVAP canister purge valve. When EGR and EVAP solenoid is not activated, vacuum signal is allowed to EGR valve and EVAP canister.
MALFUNCTION INDICATOR LIGHT (MIL)
All vehicles are equipped with a MIL on the instrument panel. Light comes on as a bulb check when the ignition switch is turned to the ON position. Light also comes on when systems related to the emission controls are malfunctioning during normal vehicle operation. For additional information, see TESTS W/CODES article.
MISCELLANEOUS CONTROLS
Note. Although not true engine performance-related systems, some controlled devices may affect driveability if they malfunction.
If A/C is turned on while engine is at idle, ECM will signal the Auxiliary Air Control (AAC) to increase idle speed. During hard acceleration, ECM cuts off the A/C power relay circuit to disengage A/C clutch for several seconds to aid acceleration.
Cooling fan motor(s) is controlled by the ECM through the cooling fan relay(s). ECM will compensate idle speed when cooling fan is on.
On models with multiple relays, one relay operates under normal or low speed operation and other operates under high speed or extra load conditions (A/C on). A third relay is sometimes used for operating the 2-speed cooling fan motor at high speed.
TRANSMISSION/TRANSAXLE CONTROLS
Some A/T models are equipped with an electronic Automatic Transmission/Transaxle Control Unit (ATCU). ATCU receives input signals from the ignition coil (RPM signal), idle switch (on-off signal), throttle sensor (variable signal) and full throttle switch (on-off signal). Based on these values, the ATCU calculates optimum timing and duration to energize shift solenoids, overrun clutch solenoid and lock-up solenoid. ATCU also indicates when Overdrive (OD) is engaged by illuminating the OD indicator light.