System Description
The MAP sensor is essentially a strain gauge used to measure the pressure in the surge tank. Inside the sensor is a metal diaphragm with a small wire attached. The diaphragm flexes according to changes in pressure. When the diaphragm flexes, the wire attached to it stretches, changing the resistance of the wire. The ECM applies 5 volts to the MAP sensor and measures the voltage drop across the sensor. Sensor output is in volts and as pressure decreases, the voltage drop across the sensor increases. Since the MAP sensor is used as an air flow sensor, the sensor signal is an important input. The ECM uses the information to determine fuel amount and ignition timing.
The Intake Air Temperature (IAT) sensor is built into the MAP sensor. The IAT sensor is a variable resistor whose resistance changes as the temperature of the air flowing through the air intake changes. The ECM uses the IAT sensor input to adjust fuel injector pulse width. When the temperature sensed is cold, the ECM enriches fuel mixture by increasing injector pulse width, as the air warms, the injector pulse width time is shortened.
The Engine Coolant Temperature (ECT) sensor is located in the coolant passage of the cylinder head. The ECT sensor is a variable resistor whose resistance changes as temperature of engine coolant flowing past sensor changes. When coolant temperature is low, sensor resistance is high; when coolant temperature is high, sensor resistance is low. ECM checks ECT sensor voltage and uses information to adjust fuel injector pulse width and ignition timing. When the temperature sensed is very cold, ECM enriches fuel mixture and advances ignition timing. As coolant temperature rises, ECM reduces amount of enrichment and timing advance.
The Throttle Position (TP) sensor mounts on the side of the throttle body and is connected to the throttle valve shaft. TP sensor is a variable resistor (potentiometer) whose resistance changes according to throttle valve shaft position. During acceleration, TP sensor resistance decreases; during deceleration, TP sensor resistance increases. The ECM applies a reference voltage to TP sensor and then measures voltage that is present on TP sensor signal circuit. ECM uses TP sensor signal to adjust timing and injector pulse width. TP sensor signal along with MAF sensor signal is used by ECM to calculate engine load.
Note. Front Heated Oxygen Sensor (HO2S) may also be referred to as Bank 1/Sensor 1 (1/1) HO2S or O2 Sensor (Up). Rear HO2S may also be referred to as Bank 1/Sensor 2 (1/2) HO2S or O2 sensor (Down).
Front Heated Oxygen Sensor (HO2S) is located on exhaust manifold and rear HO2S is located after warm-up catalytic converter. ECM uses HO2S signals to maintain the air fuel mixture at the ratio resulting in optimum fuel economy and reduced emissions. Amount of oxygen in exhaust gases indicates to front HO2S whether air fuel mixture being supplied to engine cylinders is rich or lean. Readings of rear HO2S are used to indicate efficiency of catalytic converter. ECM calculates catalytic converter efficiency by comparing rear HO2S signal to front HO2S signal.
A normal HO2S signal will constantly fluctuate above and below 500 mV, with front HO2S signal frequency of at least 5 Hz at 2500 RPM. Due to effect of catalytic converter, rear HO2S signal frequency will be lower than front HO2S signal frequency. If rear HO2S signal coincides with front HO2S signal a large percentage of the time, this indicates a loss in efficiency of catalytic converter or a malfunction within fuel system.
Note. Front Heated Oxygen Sensor (HO2S) may also be referred to as Bank 1/Sensor 1 (1/1) HO2S or O2 Sensor (Up). Rear HO2S may also be referred to as Bank 1/Sensor 2 (1/2) HO2S or O2 sensor (Down).
Front Heated Oxygen Sensor (HO2S) is located on exhaust manifold and rear HO2S is located after warm-up catalytic converter. ECM uses HO2S signals to maintain the air fuel mixture at the ratio resulting in optimum fuel economy and reduced emissions. Amount of oxygen in exhaust gases indicates, to front HO2S, whether air fuel mixture being supplied to engine cylinders is rich or lean. Readings of rear HO2S are used to indicate efficiency of catalytic converter. ECM calculates catalytic converter efficiency by comparing rear HO2S signal to front HO2S signal.
A normal HO2S signal will constantly fluctuate above and below 500 mV, with front HO2S signal frequency of at least 5 Hz at 2500 RPM. Due to effect of catalytic converter, rear HO2S signal frequency will be lower than front HO2S signal frequency. If rear HO2S signal coincides with front HO2S signal a large percentage of time, this indicates a loss in efficiency of catalytic converter or a malfunction within fuel system.
Note. Front Heated Oxygen Sensor (HO2S) may also be referred to as Bank 1/Sensor 1 (1/1) HO2S or O2 Sensor (Up). Rear HO2S may also be referred to as Bank 1/Sensor 2 (1/2) HO2S or O2 sensor (Down).
Front Heated Oxygen Sensor (HO2S) is located on exhaust manifold and rear HO2S is located after warm-up catalytic converter. ECM uses HO2S signals to maintain the air fuel mixture at the ratio resulting in optimum fuel economy and reduced emissions. Amount of oxygen in exhaust gases indicates to front HO2S whether air fuel mixture being supplied to engine cylinders is rich or lean. Readings of rear HO2S are used to indicate efficiency of catalytic converter. ECM calculates catalytic converter efficiency by comparing rear HO2S signal to front HO2S signal.
A normal HO2S signal will constantly fluctuate above and below 500 mV, with front HO2S signal frequency of at least 5 Hz at 2500 RPM. Due to effect of catalytic converter, rear HO2S signal frequency will be lower than front HO2S signal frequency. If rear HO2S signal coincides with front HO2S signal a large percentage of the time, this indicates a loss in efficiency of catalytic converter or a malfunction within fuel system.
Note. Front Heated Oxygen Sensor (HO2S) may also be referred to as Bank 1/Sensor 1 (1/1) HO2S or O2 Sensor (Up). Rear HO2S may also be referred to as Bank 1/Sensor 2 (1/2) HO2S or O2 sensor (Down).
Front Heated Oxygen Sensor (HO2S) is located on exhaust manifold and rear HO2S is located after warm-up catalytic converter. ECM uses HO2S signals to maintain the air fuel mixture at the ratio resulting in optimum fuel economy and reduced emissions. Amount of oxygen in exhaust gases indicates to front HO2S whether air fuel mixture being supplied to engine cylinders is rich or lean. Readings of rear HO2S are used to indicate efficiency of catalytic converter. ECM calculates catalytic converter efficiency by comparing rear HO2S signal to front HO2S signal.
A normal HO2S signal will constantly fluctuate above and below 500 mV, with front HO2S signal frequency of at least 5 Hz at 2500 RPM. Due to effect of catalytic converter, rear HO2S signal frequency will be lower than front HO2S signal frequency. If rear HO2S signal coincides with front HO2S signal a large percentage of the time, this indicates a loss in efficiency of catalytic converter or a malfunction within fuel system.
Air/fuel control system, in addition to a number of sensors, includes following components and systems
- Intake air system.
- Exhaust system.
- Evaporative emissions control system (includes purge control solenoid valve).
- Fuel injectors.
- Fuel pressure regulator.
- Fuel pump.
For air/fuel ratio to be within limits, all sensors, components and systems associated with air/fuel control system must function within normal parameters.
Fuel injectors are solenoid-operated valves, located on intake manifold, one for each cylinder. When a fuel injector solenoid is energized (pulsed) injector needle valve opens, allowing pressurized fuel to pass through injector and mix with air entering engine. ECM controls injector timing and pulse width. ECM pulses fuel injectors based on information provided by its network of engine sensors. ECM uses crankshaft position sensor to determine when to pulse injectors. Engine coolant temperature, intake air temperature, air flow and throttle position data are all used by ECM to calculate injector pulse width. ECM also uses its network of sensors to determine whether all injectors should be pulsed at same time (simultaneous injection) or each injector should be pulsed individually (sequential injection). Sequential injection is almost always used during normal engine operation. Simultaneous injection may be used when engine is being cranked.
With ignition switch at ON or START position, voltage is applied to ignition coil. Ignition coil assembly consists of 2 coils. Ignition coils are located on rear of cylinder head. High tension leads go to each cylinder from ignition coil. Ignition coil fires 2 spark plugs on every power stroke (cylinder under compression and cylinder on exhaust stroke). Coil number one fires cylinders 1 and 4. Coil number 2 fires cylinders 2 and 3. ECM provides a switching circuit to ground for energizing primary ignition coils. ECM uses crankshaft position sensor signal to time energizing of coil. When a primary ignition coil is energized and de-energized, secondary coil produces a high voltage spike across attached spark plugs.
Knock sensor is attached to engine cylinder block and senses engine knocking. A knocking vibration from cylinder block is applied as pressure to sensor piezoelectric element. This vibration pressure is then converted into a voltage signal. ECM uses this signal to suppress knocking by retarding ignition timing.
Crankshaft Position (CKP) sensor consists of a magnet and coil located next to the flywheel, on transaxle bell housing. Sensing wheel teeth are used by CKP sensor to generate a signal. Voltage signal from CKP sensor allows ECM to determine engine RPM and crankshaft position.
Camshaft Position (CMP) sensor is mounted on rear of cylinder head, near ignition coils. CMP senses Top Dead Center (TDC) point of No. 1 cylinder in compression stroke. CMP sensor signal allows ECM to determine fuel injector sequence starting point.
Note. Front Heated Oxygen Sensor (HO2S) may also be referred to as Bank 1/Sensor 1 (1/1) HO2S or O2 Sensor (Up). Rear HO2S may also be referred to as Bank 1/Sensor 2 (1/2) HO2S or O2 sensor (Down).
Catalyst efficiency is demonstrated in its ability to oxidize CO and HC emissions. ECM compares output signals of front and rear Heated Oxygen Sensor (HO2S) to determine whether output of rear sensor is beginning to match output of front HO2S. As catalyst wears, rear HO2S signal trace begins to match front HO2S signal trace. That is because catalyst becomes saturated with oxygen and cannot use oxygen to convert HC and CO into H2O and C02 with same efficiency as when it was new. A completely worn catalyst shows a 100 percent match between front and rear HO2S outputs.
Purge Control Solenoid Valve (PCSV) is part of Evaporative (EVAP) emission control system. PCSV controls purge air from EVAP emission canister.
Note. Idle Speed Control (ISC) motor may also be referred to as ISC Actuator (ISA).
The ISA has 2 coils that are driven by separate ECM driver stages. Depending on pulse duty factor, equilibrium of magnetic forces of 2 coils will result in different directions for magnetic forces of 2 coils which will result in different positions for ISA. In parallel to throttle valve, a bypass hose line is arranged where ISA is inserted.
The acceleration sensor is located on a bracket on right front strut tower, when accelerating or driving on a rough road, ECM uses the accelerator sensor input signal to avoid false misfire detection.
Note. Idle Speed Control (ISC) motor may also be referred to as ISC Actuator (ISA).
The ISA has 2 coils that are driven by separate ECM driver stages. Depending on pulse duty factor, equilibrium of magnetic forces of 2 coils will result in different directions for magnetic forces of 2 coils which will result in different positions for ISA. In parallel to throttle valve, a bypass hose line is arranged where ISA is inserted.
Note. Idle Speed Control (ISC) motor may also be referred to as ISC Actuator (ISA).
The ISA has 2 coils that are driven by separate ECM driver stages. Depending on pulse duty factor, equilibrium of magnetic forces of 2 coils will result in different directions for magnetic forces of 2 coils which will result in different positions for ISA. In parallel to throttle valve, a bypass hose line is arranged where ISA is inserted.