MONITOR DESCRIPTION
After the ECM sends the "target" duty-cycle signal to the OCV (Oil Control Valve), the ECM monitors the OCV current to establish an "actual" duty-cycle. When the actual duty-cycle ratio varies from the target duty-ratio, the ECM sets a DTC.
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The ECM optimizes the valve timing using the VVT (Variable Valve Timing) system to control the intake valve camshaft. The VVT system includes the ECM, the OCV (Oil Control Valve) and the VVT controller. The ECM sends a target "duty-cycle" control signal to the OCV. This control signal, applied to the OCV, regulates the oil pressure supplied to the VVT controller. The VVT controller can advance or retard the intake valve camshaft.
Example
A DTC will set if: 1) the difference between the target and actual valve timing is more than 5 degrees of the crankshaft angle (CA) and the condition continues for more than 4.5 sec.; or 2) the OCV is forcibly activated 63 times or more.
Advanced cam DTCs are subject to "1 trip" detection logic.
Retarded cam DTCs are subject to "2 trip" detection logic.
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The ECM optimizes the valve timing using the VVT (Variable Valve Timing) system to control the intake valve camshaft. The VVT system includes the ECM, the OCV (Oil Control Valve) and the VVT controller. The ECM sends a target duty-cycle control signal to the OCV. This control signal, applied to the OCV, regulates the oil pressure supplied to the VVT controller. The VVT controller can advance or retard the intake valve camshaft. The ECM calibrates the valve timing of the VVT system by setting the camshaft to the maximum retard angle when the engine speed is idling. The ECM closes the OCV to retard the cam. The ECM stores this value as VVT learning value (When the difference between the target valve timing and the actual valve timing is 5 degrees or less, the ECM stores this in its memory).
If the learning value meets both of the following conditions ((a) and (b)), the ECM interprets this as a defect in the VVT system and set a DTC.
- VVT learning value is less than 19°CA (crankshaft angle), or more than 41 °CA.
- Above condition continues for more than 18 sec.
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The sending 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 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 0.4 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 IAT (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 is 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 resistance varies as output voltage from the sensor changes.
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 condition continues for 0.5 sec. or more, the ECM will set a DTC.
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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.
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 an expected specific voltage difference 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 the range of +/- 0.02 V of VTA2, the ECM interprets this as a short circuit in the throttle position sensor system and will set a DTC.
The ECM uses throttle position sensor to monitor the throttle valve opening angle.
This sensor includes 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 ECT (Engine Coolant Temperature) 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 cause 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, the ECM interprets this as a fault in the sensor or cooling system and sets a DTC.
Example
The engine coolant temperature is 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 information to regulate the air-fuel ratio close to a stoichiometric ratio. This maximizes the catalytic converter's ability to purify the exhaust gas. The sensor detects oxygen levels in the exhaust gas and sends this signal to the ECM.
The inner surface of the sensor element is exposed to outside air. The outer surface of the sensor element is exposed to exhaust gas. The sensor element is made of platinum coated zirconia and includes an integrated heating element. The heated oxygen sensor has the characteristic whereby its output voltage changes suddenly in the vicinity of the stoichiometric air-fuel ratio. The heated oxygen sensor generates waveforms of a voltage between 0 V and 1 V in response to the oxygen concentration in exhaust gas. When the output voltage of the heated oxygen sensor is 0.55 V or more, the ECM judges that the air-fuel ratio is RICH. When it is 0.40 V or less, the ECM judges that the air-fuel ratio is LEAN.
The ECM monitors the response feature of the heated oxygen sensor. If the response time of the sensor output status change from RICH to LEAN or vice versa becomes longer, the ECM interprets this as a malfunction in the heated oxygen sensor and sets 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 0.5 V, the air-fuel ratio is RICH. If the sensor does not indicate RICH even once despite the conditions for the closed-loop fuel control being met and a specified time period has passed, 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 3 items
- If the rear heated oxygen sensor voltage changes between Rich and Lean while the vehicle is running (repeating acceleration and deceleration), the ECM interprets this as a malfunction and illuminates the MIL, and then sets a 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, the ECM interprets this as a malfunction, illuminates the MIL, and then sets DTC.
- If the sensor's voltage drops to below 0.2 V (extremely Lean status) immediately when the vehicle decelerates and the fuel cut is working, the ECM interprets this to mean the sensor's response feature has deteriorated and 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 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 the normal range, the ECM interprets this as a fault in the knock sensor and sets a DTC.
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If there are no signals 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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The evaporative emission system consists of the vapor pressure sensor, the CCV (Canister Closed Valve), the pressure switching valve and the EVAP VSV (Purge VSV), those are used to detect malfunction in the system by ECM.
This test will run once per driving cycle when the ECM detects stable vapor pressure in the fuel tank. While the vehicle is being driven on rough or winding roads, the movement of the fuel in the tank will cause unstable fuel tank vapor pressure and the diagnostic test will not executed.
The ECM perform the following steps
- The CCV is closed, (shuts the system)
- Checks the stability of the fuel tank pressure. If the variation in the pressure is greater than the specified value, disables the diagnosis.
- Opens the EVAP VSV to introduce a negative pressure (vacuum) from the intake manifold into the fuel tank.
- Closes the EVAP VSV to seal the fuel tank for storing the negative pressure.
- Monitors the negative pressure in the fuel tank for: Rapid decrease, i.e. a large leak, 0.040 inch or more Decrease greater than the normal value If the ECM detects either of above conditions, the ECM interprets this as a leak in the EVAP system. The ECM will illuminate the MIL (2-trip detection logic) and set a DTC.
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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 being driven when the over 30 sec. have passed since the park/neutral position switch was turned OFF. If there is no signal from the vehicle speed sensor when these conditions are satisfied, the ECM concludes that the vehicle speed sensor is malfunctioning. The ECM will turn on the MIL and a DTC is set.
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The idle speed is controlled by the ETCS (Electronic Throttle Control System).
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 TCM 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 learning value of the idle speed control remains at the maximum or minimum five times or more during a driving 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 200 (*1) rpm five times during a drive cycle, the ECM will turn on the MIL and a DTC is set.
HINT
*1: 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 to 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 appear, the ECM does not store another DTC.
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The ECM continuously monitors its 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 0.4 V for 0.8 seconds, the ECM concludes that the power supply circuit has an open circuit. The MIL is turned on and a DTC is set.
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 (Electronic Throttle Control System). 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 is 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 deviates 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.
The ECM observes the pressure in the secondary air passage using the pressure sensor located on the air switching valve in the secondary air injection system.
If there is a defect in the sensor or the sensor circuit, the voltage level will deviate from the normal operating range, the ECM interprets this deviation as a defect in the pressure sensor circuit and sets a DTC.
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The ECM observes the pressure in the secondary air passage using the pressure sensor located on the air switching valve in the secondary air injection system. The sensor detects an exhaust pressure in the secondary air passage.
If the ECM receives the pulsation signal from the sensor despite the ECM ordering the VSV to close the air switching valve, or if the ECM has not received the signal from the sensor despite the ECM ordering the VSV to open the valve, the ECM interprets this as a fault in the secondary air injection system and sets a DTC.
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The ECM observes the pressure in the secondary air passage using the pressure sensor located on the air switching valve in the secondary air injection system. The sensor measures the pressure in the secondary air passage and sends a signal to the ECM.
If the pressure level from the sensor has not reached a certain level despite the ECM turning on the air pump, or if the pressure level exceeds the threshold despite the ECM turning off the air pump, the ECM interprets this as a fault in the secondary air injection system and sets a DTC.
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When the engine RPM is high, the VVTL-i actuator advances shims under the high-lift cam followers using engine oil pressure. Switching to the high-lift cam increases the valve lift as well as the intake air volume and exhaust capacity. These changes increase the engine's power output.
When the engine RPM is 6,000 rpm or more, the ECM increases the OCV control signal duty-ratio and it opens the oil passage to the VVTL-i actuator. The engine oil pressure powered actuator advances the cam follower shims and valves begin using the high-lift cam.
The ECM senses the current flow to the OCV to determine the "actual" duty-ratio of the control signal. If the duty-ratio is out of the normal range, the ECM interprets this as malfunction in the OCV. The ECM will illuminate the MIL and a DTC is set.
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When the engine RPM is high, the VVTL-i actuator advances shims under the high-lift cam followers using engine oil pressure. Switching to the high-lift cam increases the valve lift as well as the intake air volume and exhaust capacity. These changes increase the engine's power output.
When the engine RPM is 6,500 rpm or more, the ECM increases the OCV control signal duty-ratio and it opens the oil passage to VVTL-i actuator. The engine oil pressure powered actuator advances the cam follower shims and valves begin using the high-lift cam.
The VVTL-i oil pressure switch senses the engine oil pressure applied to the VVTL-i system and the ECM judges which cam (standard cam or high-lift cam) is used based on the switch output. If the engine oil pressure applied to the VVTL-i system is high when the standard cam is required by the ECM or if the pressure is low when the high-lift cam is required, the ECM will determine that there is a malfunction OCV for VVTL and set a DTC.
