MONITOR DESCRIPTION
After the ECM sends the "target" duty-cycle signal to the OCV, the ECM monitors the OCV current to establish an "actual" duty-cycle. The ECM detects a malfunction and sets a DTC when the actual duty-cycle ratio varies from the target duty-cycle ratio.
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The ECM optimizes the valve timing using the Variable Valve Timing (VVT) system to control the intake valve camshaft. The VVT system includes the ECM, the Oil Control Valve (OCV) 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
When a difference between the targeted and actual valve timing is more than 5° camshaft angle "CA" and this condition continues more than 4.5 sec, and if 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 Variable Valve Timing (VVT) system to control the intake valve camshaft. The VVT system includes the ECM, the Oil Control Valve (OCV) 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 valve as "VVT learned value" (When the difference between the target valve timing and the actual valve timing is 5° or less, the ECM learns it).
If the learned 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 21° CA or more than 40° CA.
- Above condition continues for more than 18 second.
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The ECM uses the Air Fuel Ratio sensor (A/F sensor) information to regulate the air/fuel ration close to a stoichiometric ratio. This maximizes the catalytic converter's ability to purify exhaust gases. 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 zirconia element generates a small voltage when there is a large difference in the oxygen concentrations of the exhaust and the outside air. The platinum coating amplifies the voltage generation. When heated, the sensor becomes very efficient. If the temperature of the exhaust is low, the sensor will not generate useful voltage signals without supplemental heating. The ECM regulates the supplemental heating using a duty-cycle approach to regulate the average current in the heater element. If the heater current is out of the normal range, the sensor's output signals will be inaccurate and the ECM can not regulate the A/F ratio properly. When the heater current is out of the normal operating range, the ECM interprets this as a malfunction and sets a DTC.
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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 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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Refer to «PRE-CHECK» for detailed information on MODE 06 DATA.
If there is a defect in the sensor 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 MAF sensor and sets a DTC.
Example
When the sensor voltage output is less than 0.2 V or more than 4.9 V and if either condition continues more than 3 sec.
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The MAF (Mass Air Flow) sensor 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 MAF sensor, 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 in internal thermister, changing their resistance. To maintain a constant current value, the ECM varies the voltage applied to these components in the MAF sensor. The voltage level is proportional to the air flow through the sensor and the ECM interprets this voltage as the intake air amount. If there is a defect in the sensor 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 MAF sensor and sets a DTC.
Example: If the voltage is outside the range of 0.4 V to 2.2 V, the ECM interprets this as a defect in the MAF sensor 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 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 -40°C (-40°F) and if either condition continues 0.5 sec or more.
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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.
Example
When the ECM calculates that the ECT is -40°C (-40°F) or more than 140°C (284°F) and if either condition continues 0.5 sec or more, the ETC 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 coolant temperature (ECT) was between 35°C (95°F) and 60°C (140°F). If after driving for 250 seconds, the ECT still remains within 3°C (5.4°F) of the staring temperature, a DTC will be set. (2 trip detection logic)
- Upon starting the engine, the coolant temperature (ECT) was over 60°C (140°F). If after driving for 250 seconds, 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.
- VTA1 and VTA2 each have a specific voltage operating range.
- VTA1 and VTA2 should never be close to the same voltage levels.
If the difference between VTA1 and VTA2 is incorrect (a), the ECM interprets this as a fault and will set a DTC.
If VTA1 or VTA2 is out of the normal operating range (b), the ECM interprets this as a fault and will set a DTC. If VTA1 is within 0.02 V of VTA2 (c), 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.
- VTA1 and VTA2 each have a specific voltage operating range.
- VTA1 and VTA2 should never be close to the same voltage levels.
If the difference between VTA1 and VTA2 is incorrect (a), the ECM interprets this as a fault and will set a DTC.
If VTA1 and VTA2 is out of the normal operating range (b), the ECM interprets this as a fault and will set a DTC.
If VTA1 is within 0.02 V of VTA2 (c), the ECM interprets this as a short circuit in the throttle position sensor system and will set a DTC.
DTC P0121 relates to condition (a) above.
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.
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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 warm enough for closed-loop fuel control, the ECM interprets this as a fault in the sensor or cooling system.
Example
The engine coolant temperature was 0°C (32°F) at engine start. After 5 minutes running time, the coolant temperature sensor still indicates that the engine is not warm enough to begin active 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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When the sensor output remains RICH or LEAN even though the vehicle has been accelerating and slow for 5 to 8 minutes, the ECM interprets this as a fault in the rear oxygen sensor. Also, if the rear oxygen sensor output remains at less than 0.05 V for more than 270 seconds (when ECM monitored the oxygen sensor for 300 seconds while the air fuel feed back is being performed), the ECM will interpret this as a fault. In either case, the ECM will turn on the MIL and set a DTC.
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- Connect the hand-held tester to the DLC3.
- Switch the hand-held tester from the normal mode to the check (test) mode (See «PRE-CHECK» ).
- Start the engine and let the engine idle for 60 seconds or more.
- Drive the vehicle at 25 mph (40 km/h) or more for 40 seconds or more.
- Let the engine idle for 10 seconds or more.
- Perform steps (d) to (e) 12 times.
HINT
If a malfunction exists, the MIL will be illuminated on the multi-information display during step (f).
Note. If the conditions in this test are not strictly followed, detection of a malfunction will not occur. If you do not have a hand - held tester, turn the ignition switch OFF after performing steps from (c) to (f), then perform steps from (c) to (f) again.
If the output signal remains low or high for more than 10 seconds, the ECM interprets this as a fault in' knock sensor and sets a DTC.
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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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'there is no signal from the VVT 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 ECM uses sensors mounted before and after the three-way catalyst (TWC) to monitor its' efficiency. The first sensor, an air fuel ratio sensor (A/F sensor 1), sends pre-catalyst A/F ratio information to the ECM. The second sensor, a heated oxygen sensor (O2S) sends post-catalyst information to the ECM. The ECM compares these two signals to judge the efficiency of the catalyst and the catalyst's ability to store oxygen. During normal operation, the TWC stores and releases oxygen as needed. The capacity to store oxygen results in a low variation in the post-TWC exhaust stream as shown below.
If the catalyst is functioning normally, the waveform of the heated oxygen sensor located behind the catalyst slowly switches back and forth between rich and lean.
When the waveform of the heated oxygen sensor located behind the catalyst alternates frequently between rich and lean, it indicates that catalyst performance has deteriorated. As the catalyst efficiency degrades, its ability to store oxygen is reduced and the catalyst output becomes more variable.
When the running the monitor, the ECM compares sensor 1 and sensor 2 signals over a specific time to determine catalyst efficiency. The ECM begins by calculating the signal length for both sensors.
The ECM uses the signal length values of rear oxygen sensor output voltage. If the signal length is greater than the failure threshold (which varies with A/F sensor signal length), the ECM interprets this as a fault the catalyst. The ECM will turn on the MIL and a DTC will be set.
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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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Refer to «PRE-CHECK» for detailed information on MODE 06 DATA.
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- Connect the OBD II scan tool or the hand-held tester to the DLC3.
- Start the engine and warm it up with all the accessories switched OFF until the engine coolant temperature is stable.
- Run the engine at 2,500 to 3,000 RPM for about 3 minutes.
- When running the engine at 3,000 RPM for 2 seconds and 2,000 RPM for 2 seconds alternately, check the waveform of the oxygen sensor (bank 1 sensor 2).
The ECM tests the evaporative emissions (EVAP) system using the fuel tank pressure sensor, the canister close valve (CCV), and the VSV for EVAP. 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)
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 RPM of the transmission counter gear indicates more than 300 RPM and it has been over 30 seconds since the park/neutral position switch was turned OFF. 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).
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 Electronic Throttle Control System (ETCS). If the actual idle RPM varies more than a specified amount or a learned value of the idle speed control remains at the maximum or remains at minimum five times or more during a trip, the ECM concludes that there is a problem with the idle speed control ECM function. The ECM will turn on the MIL and a DTC is set.
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 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. At the next engine start, the ECM will turn on the MIL and a DTC will be set.
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HINT
If DTC P0560 is present, the ECM will not store other DTCs.
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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 random access memory (RAM) errors. The two CPUs also perform continuous mutual monitoring. If there is a difference between outputs from the two CPUs that deviates from standard level ranges, the ECM concludes that there is a fault and sets a DTC. Additionally, if the signals to the throttle actuator deviate from the standard range or if the ECM detects a malfunction in the throttle actuator supply voltage, the ECM will conclude that there is a fault and set a DTC. With any malfunction of the ECM, the MIL will be turned on a DTC (s) will be set.
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While the engine is being cranked, the battery positive voltage is applied to terminal STA of the ECM. If the ECM detects the starter control signal (STA) while the vehicle is driving, it will conclude that there is a fault in the starter control circuit. The ECM will turn on the MIL and a DTC is set.
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The ECM monitors the current flows through the electronic throttle motor and detects malfunctions or an open circuit in the throttle motor based on the current value. When the current deviates from standard range, the ECM concludes that there is a fault in the throttle motor ECM turns on MIL and a DTC is set.
Example
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.
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The ECM concludes that there is a malfunction of the electronic throttle control system 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.
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The ECM monitors the battery supply voltage applied to the electronic throttle motor. When the power supply voltage drops below the threshold, the ECM concludes that there is an open in the power supply circuit. A DTC is set and the MIL is turned on.
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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 system. The ECM turns on the MIL and a DTC is set.
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When either voltage output VPA or VPA2, deviates from the standard ranges, or 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.
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The accelerator pedal position sensor is mounted on the accelerator pedal bracket and consists of two sensors VPA and VPA2. The VPA is used to detect accelerator pedal position, and the VPA2 is used to monitor the VPA and detect faults in the sensor itself. When difference between voltage outputs, of the VPA or VPA2 deviates from the standard range, 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.
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Under the air-fuel ratio feedback control, if the voltage output of the A/F sensor indicates RICH or LEAN for a certain period of time or more, the ECM concludes that there is a fault in the A/F sensor system. The ECM will turn on the MIL and a DTC is set.
If the A/F sensor voltage output is less than 2.8 V (indicates very RICH) 10 seconds even though voltage output of the heated oxygen sensor output voltage is less than 0.85 V, the ECM sets DTC P2196 or DTC P2198. Also, if the heated oxygen sensor output voltage is 0.15 V or more, but the A/F sensor voltage output is more than 3.8 V (indicates very LEAN) 10 seconds, DTC P2195 or DTC P2197 is set.
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- Connect the hand-held tester to the DLC3.
- Switch the hand-held tester from the normal mode to the check mode (See «PRE-CHECK» ).
- Start the engine and warm it up with all the accessory switches OFF.
- Drive the vehicle at 38 to 75 mph (60 to 120 km/h) and engine speed at 1,400 to 3,200 RPM for 3 to 5 min.
HINT
If a malfunction exists, the MIL will be illuminated during step (d).
Note. If the conditions in this test are not strictly followed, detection of a malfunction will not occur. If you do not have a hand-held tester, turn the ignition switch OFF after performing steps (c) and (d), then perform steps (c) and (d) again.
The air fuel ratio (A/F) sensor has a characteristic that it varies its voltage output in proportion to the air-fuel ratio. If impedance (alternating current resistance) or voltage output of the sensor extraordinarily deviates from the standard range, the ECM determines to detect open or short malfunction in the A/F sensor circuit.
