MONITOR DESCRIPTION
The sensing portion of the heated oxygen sensor has a zirconia element which is used to detect oxygen concentration in the exhaust. if the zirconia element is at the proper temperature and difference of the oxygen concentration between the inside and outside surface of sensor is large, the zirconia element will generate voltage signals. in order to increase the oxygen concentration detecting capacity in the zirconia element, the ECM supplements the heat from the exhaust with heat from a heating element inside the sensor. When current in the sensor is out of the standard operating range, the ECM interprets this as a fault in the heated oxygen sensor and sets a DTC.
Example
The ECM will set a high current dtc if the current in the sensor is more than 2.0 a when the heater is off. Similarly, the ECM will set a low current DTC if the current is less than 0.25 a when the heater is on.
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If there is a defect in the MAP (Mass Air Flow) meter or an open or short circuit, the voltage level will deviate outside the normal operating range. The ECM interprets this deviation as a defect in the MAP meter and sets a DTC.
Example
When the MAP meter voltage output is less than 0.2 V, or more than 4.9 V, and if either the condition continues for more than 3 sec.
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The MAP (Mass Air Flow) meter helps the ECM calculate the amount of air flowing through the throttle valve.
The ECM uses this information to determine the fuel injection time and provide a proper air fuel ratio. Inside the MAP meter, there is a heated platinum wire exposed to the flow of intake air. By applying a specific current to the wire, the ECM heats this wire to a given temperature. The flow of incoming air cools the wire and an internal thermistor, affecting their resistance. To maintain a constant current value, the ECM varies the voltage applied to these components in the MAP meter. The voltage level is proportional to the air flow through the MAP meter. The ECM interprets this voltage as the intake air amount. If there is a defect in the MAP meter or an open or short circuit, the voltage level will deviate outside the normal operating range. The ECM interprets this deviation as a defect in the MAP meter and sets a DTC.
Example
If the voltage is more than 2.2 V at idle or less than 0.25 V at idle OFF, the ECM interprets this as a defect in the MAP meter and sets a DTC.
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The ECM monitors the sensor voltage and uses this value to calculate the intake air temperature. When the sensor output voltage deviates from the normal operating range, the ECM interprets this as a fault in the IAT sensor and sets a DTC.
Example
When the sensor voltage output equal to -40°C (-40°F), or more than 140°C (284°F).
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The ECT (Engine Coolant Temperature) sensor is used to monitor the engine coolant temperature. The ECT sensor has a thermistor that varies its resistance depending on the temperature of the engine coolant. When the coolant temperature is low, the resistance in the thermistor increases. When the temperature is high, the resistance drops. The variations in resistance are reflected in the voltage output from the sensor.
The ECM monitors the sensor voltage and uses this value to calculate the engine coolant temperature.
When the sensor output voltage deviates from the normal operating range, the ECM interprets this as a fault in the ECT sensor and sets a DTC.
Example
When the ECM calculates that the ECT is less than -40°C (-40°F), or more than 140°C (284°F), and if either the condition continues for 0.5 sec. or more, the ECM will set a DTC.
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The Engine Coolant Temperature (ECT) sensor is used to monitor the engine coolant temperature. The ECT sensor has a thermistor that varies its resistance depending on the temperature of the engine coolant. When the coolant temperature is low, the resistance in the thermistor increases. When the temperature is high, the resistance drops. The variations in resistance are reflected in the voltage output from the sensor. The ECM monitors the sensor voltage and uses this value to calculate the engine coolant temperature. When the sensor output voltage deviates from the normal operating range, the ECM interprets this as a fault in the ECT sensor and sets a DTC.
Examples
- Upon starting the engine, the ECT is between 35°C (95°F) and 60°C (140°F). If after driving for 250 sec., the ECT still remains within 3°C (5.4°F) of the starting temperature, a DTC will be set (2 trip detection logic).
- Upon starting the engine, the ECT is over 60°C (140°F). If after driving for 250 sec., the ECT still remains within 1°C (1.8°F) of the starting temperature, a DTC will be set (6 trip detection logic).
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The ECM uses throttle position sensor to monitor the throttle valve opening angle.
- There is a specific voltage difference expected between VTA1 and VTA2 for each throttle opening angle. If the difference between VTA1 and VTA2 is incorrect the ECM interprets this as a fault and will set a DTC.
- VTA1 and VTA2 each have a specific voltage operating range. If VTA1 or VTA2 is out of the normal operating range the ECM interprets this as a fault and will set a DTC.
- VTA1 and VTA2 should never be close to the same voltage levels. If VTA1 is within 0.02 V of VTA2 the ECM interprets this as a short circuit in the throttle position sensor system and will set a DTC.
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The ECM uses throttle position sensor to monitor the throttle valve opening angle.
This sensor including two signals, VTA1 and VTA2. VTA1 is used to detect the throttle opening angle and VTA2 is used to detect malfunctions in VTA1.
There are several checks that the ECM performs confirm proper operation of the throttle position sensor and VTA1.
There is a specific voltage difference expected between VTA1 and VTA2 for each throttle opening angle. If the voltage output difference of the VTA1 and VTA2 deviates from the normal operating range, the ECM interprets this as a malfunction of the throttle position sensor. The ECM will turn on the MIL and a DTC is set.
The Engine Coolant Temperature (ECT) sensor is used to monitor the temperature of the engine coolant. The resistance of the sensor varies with the actual coolant temperature. The ECM applies a voltage to the sensor and the varying resistance of the sensor causes the signal voltage to vary. The ECM monitors the ECT signal voltage after engine start-up. If, after sufficient time has passed, the sensor still reports that the engine is not warmed up enough for closed-loop fuel control after sufficient time has passed, the ECM interprets this as a fault in the sensor or cooling system and sets a DTC.
Example
The engine coolant temperature was 0°C (32°F) at engine start. After 5 min. running time, the ECT sensor still indicates that the engine is not warmed up enough to begin air fuel ratio feedback control of the air-fuel ratio. The ECM interprets this as a fault in the sensor or cooling system and will set a DTC.
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The ECM uses the heated oxygen sensor to optimize the air-fuel mixture in closed-loop fuel control. This control helps decrease exhaust emissions by providing the catalyst with a nearly stoichiometric mixture.
The sensor detects the oxygen level in the exhaust gas and the ECM uses this data to control the air-fuel ratio. The sensor output voltage ranges from 0 V to 1 V. If the signal voltage is less than 0.4 V, the air-fuel ratio is LEAN. If the signal voltage is more than 0.55 V, the air-fuel ratio is RICH. If the conditions for the closed-loop fuel control are met and after a specified time-period, the sensor's output signal never indicates RICH, the ECM will conclude that the closed-loop fuel control is malfunctioning. The ECM will illuminate the MIL and a DTC is set.
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The ECM monitors the rear heated oxygen sensor in the following items
- If the rear heated oxygen sensor voltage changes between Rich and Lean while the vehicle is running (repeating acceleration and deceleration). If not, the ECM interprets this as a malfunction, illuminates the MIL, and then sets DTC.
- If the rear heated oxygen sensor voltage does not remain at less than 0.05 V for a long time while the vehicle is running. If not, the ECM interprets this as a malfunction, illuminates the MIL, and then sets DTC.
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The knock sensor located on the cylinder block, detects spark knock.
When spark knock occurs, the sensor pick-up vibrates in a specific frequency range. When the ECM detects the voltage in this frequency range, it retards the ignition timing to suppress the spark knock.
The ECM also senses background engine noise with the knock sensor and uses this noise to check for faults in the sensor. If the knock sensor signal level is too low for more than 10 sec., and if the knock sensor output voltage is out of normal range, the ECM interprets this as a fault in the knock sensor and sets a DTC.
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If there is no signal from the crankshaft sensor even though the engine is revolving, the ECM interprets this as a malfunction of the sensor.
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If there is no signal from the camshaft position sensor even though the engine is turning, or if the rotation of the camshaft and the crankshaft is not synchronized, the ECM interprets this as a malfunction of the sensor.
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The vehicle is equipped with two heated oxygen sensors. One is mounted upstream from the TWC (Three-Way Catalytic) converter (Front Oxygen Sensor, "sensor 1"), the second is mounted downstream (Rear Oxygen Sensor "sensor 2"). The catalyst efficiency monitor compares the sensor 1 and sensor 2 signals in order to calculate TWC ability to store the oxygen.
During normal operation, the TWC stores and releases oxygen as needed. This results in low oxygen variations in the post TWC exhaust stream as shown below.
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HINT
- Bank 1 refers to the bank that includes cylinder No.1.
- Bank 2 refers to the bank that does not include cylinder No.1.
- Sensor 1 refers to the sensor closest to the engine assembly.
- Sensor 2 refers to the sensor farthest away from the engine assembly.
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The ECM tests the Evaporative Emissions (EVAP) system using the fuel tank pressure sensor, the Canister Close Valve (CCV), and the EVAP VSV. The ECM closes the EVAP system and introduces a negative pressure (vacuum) into it. The ECM then monitors the internal pressure using the fuel tank pressure sensor (refer to graphic).
P0441
The EVAP VSV
- Is used to purge the evaporative emissions from the fuel tank into the intake manifold.
- Works with the CCV to create a negative pressure (vacuum) inside the fuel tank, and performs leak tests.
Opening or closing malfunctions in the EVAP VSV prompt the ECM to set DTC P0441.
The ECM checks for a EVAP VSV "stuck closed" fault by commanding the EVAP VSV open with the CCV (vent) closed. The fuel tank should develop a high negative pressure (vacuum). If it does not, the ECM determines that despite an OPEN command, the EVAP VSV remained closed. The ECM turns on the MIL and a DTC is set.
The ECM checks for a EVAP VSV "stuck open" fault by commanding both the EVAP VSV and CCV closed at a time when the fuel tank is at atmospheric pressure. If the fuel tank develops a high negative pressure (vacuum) during this early stage of the test, the ECM determines that the EVAP VSV is stuck open. The ECM will turn on the MIL and DTC is set.
P0446
The CCV is open under normal conditions. The CCV is used to
- After the EVAP VSV purges the evaporative emissions from the fuel tank to the intake manifold, the CCV draws fumes from the fuel tank into the charcoal canister.
- Relieve pressure inside the fuel tank when the pressure has suddenly risen.
- Along with the EVAP VSV, it creates a negative pressure (vacuum) inside the fuel tank and performs leak tests.
The ECM checks for a CCV "stuck closed" malfunction by commanding both valves (EVAP VSV and CCV) open at a time when the fuel tank is at atmospheric pressure. If the fuel tank develops a high negative pressure (vacuum) and it remains in that state for more than 4 seconds, the ECM determines that the CCV (vent) is stuck closed. The ECM will turn on the MIL and a DTC is set. This malfunction is detected regardless of the engine coolant temperature.
The ECM checks for a CCV "stuck open" malfunction by commanding the EVAP VSV open with the CCV closed when the fuel tank should have developed a high negative pressure (vacuum). If the fuel tank did not develop the proper high negative pressure (vacuum), the ECM concludes that the CCV must have been "stuck open". The ECM will turn on the MIL and a DTC is set.
P0442, P0455 and P0456
A leak in the evaporative emission system prompts the ECM to set DTC P0442, P0455 or P0456.
The ECM checks for leaks in the system by introducing a high negative pressure (vacuum) from the intake manifold by commanding the EVAP VSV open while the CCV (vent) is closed. After sufficient time has elapsed the fuel tank should have developed a high negative pressure (vacuum) and the EVAP VSV is closed. The ECM then monitors the pressure-rise (loss of vacuum) in the fuel tank. If the pressure rises too rapidly, the ECM concludes that there is a leak in the system. The ECM will turn on the MIL and a DTC is set.
The ECM has separate DTCs for small and large leaks
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- DTC P0442 is set when the internal fuel tank pressure has a large increase and the EVAP system has a small leak.
- DTC P0455 is set when EVAP system has a very large leak. Even though the ECM sends a signal to the EVAP VSV (when CCV is closed) to create a vacuum, the internal fuel tank pressure does not decrease beyond a specified level.
- DTC P0456 is set when the internal fuel tank pressure increase slightly and the EVAP system has a very small leak.
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DTC "P0451, P0452 or P0453" is recorded by the ECM when the vapor pressure sensor malfunctions.
The ECM assumes that the vehicle is driven when the park/neutral position switch is OFF and it has been over 4 sec. since the actual vehicle speed was 9 km/h (6 mph) or more.
If there is no signal from the vehicle speed sensor with these conditions satisfied, the ECM concludes that there is a fault in the vehicle speed sensor. The ECM will turn on the MIL and a DTC is set.
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The idle speed is controlled by the Electronic Throttle Control System (ETCS).
The ETCS is composed of the throttle motor which operates the throttle valve, and the throttle position sensor, which detects the opening angle of the throttle valve.
The ECM controls the throttle motor to provide the proper throttle valve opening angle to obtain the target idle speed.
The ECM regulates the idle speed by opening and closing the throttle valve using the ETCS. The ECM concludes that the idle speed control ECM function is malfunctioning if: 1) the actual idle RPM varies more than the specified amount, or 2) a learned value of the idle speed control remains at the maximum or minimum five times or more during a drive cycle. The ECM will turn on the MIL and set a DTC.
Example
If the actual idle RPM varies from the target idle RPM by more than 100 RPM* five times during a drive cycle, the ECM will turn on the MIL and a DTC is set.
HINT
* RPM threshold varies with engine load.
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The battery supplies electricity to the ECM even when the ignition switch is OFF. This electricity allows the ECM store data such as DTC history, freeze frame data, fuel trim values, and other data.
If the battery voltage falls below a minimum level, the ECM will conclude that there is a fault in the power supply circuit. The next time the engine starts, the ECM will turn on the MIL and a DTC will be set.
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HINT
If DTC P0560 present, the ECM will not store another DTC.
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*1: The DTC is set immediate. The MIL will be illuminated after the next engine start.
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The ECM continuously monitors it's internal memory status, internal circuits, and output signals to the throttle actuator. This self-check insures that the ECM is functioning properly. If any malfunction is detected, the ECM will set the appropriate DTC and illuminate the MIL.
The ECM memory status is diagnosed by internal "mirroring" of the main CPU and the sub CPU to detect RAM (Random Access Memory) errors. The two CPUs also perform continuous mutual monitoring.
The ECM sets a DTC if: 1) outputs from the 2 CPUs are different and deviate from the standards, 2) the signals to the throttle actuator deviate from the standards, 3) a malfunction is found in the throttle actuator supply voltage, and 4) any other ECM malfunction is found.
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While the engine is being cranked, the battery positive voltage is applied to terminal STA of the ECM. If the vehicle is being driven and the ECM detects the starter control signal (STA), the ECM concludes that the starter control circuit is malfunctioning. The ECM will turn on the MIL and a DTC is set.
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The ECM monitors the current through the electronic throttle motor and detects malfunctions or open circuit in the throttle motor based on the voltage of the current. When the current deviates from the standard, the ECM concludes that there is a fault in the throttle motor.
Or, if the throttle valve is not functioning properly (for example, stuck ON) the ECM concludes that there is a fault and turns on the MIL and a DTC is set.
Example
When the current is more than 10 A. Or the current is less than 0.5 A when the motor driving duty ratio is exceeding 80%. The ECM concludes that the current is out of range, turns on the MIL and a DTC is set.
The ECM concludes that there is a malfunction of the ETCS when the throttle valve remains at a fixed angle despite high drive current from the ECM. The ECM will turn on the MIL and a DTC is set.
The ECM monitors the battery supply voltage applied to the electronic throttle motor +BM. When the power supply voltage drops below the threshold, the ECM concludes that the power supply has an open circuit. A DTC is set and the MIL is turned on.
The ECM determines the "actual" throttle angle based on the throttle position sensor signal. The "actual" throttle position is compared to the "target" throttle position commanded by the ECM. If the difference of these two values exceeds a specified limit, the ECM interprets this as a fault in the ETCS. The ECM turns on the MIL and a DTC is set.
When VPA or VPA2, deviates from the standard, or the difference between the voltage outputs of the two sensors is less than threshold, the ECM concludes that there is a defect in the accelerator pedal position sensor. The ECM turns on the MIL and a DTC is set.
Example
When the voltage output of the VPA below 0.2 V or exceeds 4.8 V.
The accelerator pedal position sensor is mounted on the accelerator pedal bracket. The accelerator pedal position sensor has 2 sensor elements/signal outputs: VPA1 and VPA2. VPA1 is used to detect the actual accelerator pedal angle (used for engine control) and VPA2 is used to detect malfunctions in VPA1. When the difference between the voltage outputs of VPA1 and VPA2 deviate from the standard, the ECM concludes the accelerator pedal position sensor has a malfunction. The ECM turns on the MIL and a DTC is set.