Engine Control System (Diagnostic Codes (P0010-P0390)): Overview Lexus GX J150

DESCRIPTION

1. These DTCs are designed to detect opens or shorts in the camshaft timing oil control valve circuit. If the camshaft timing oil control valve duty cycle is excessively high or low while the engine is running, the ECM will illuminate the MIL and store the DTC.
2. The VVT (variable valve timing) system adjusts the intake and exhaust valve timing to improve driveability. The engine oil pressure turns the camshaft timing gear to adjust the valve timing. The camshaft timing oil control valve is a solenoid valve and switches the engine oil line. The valve moves when the ECM applies 12 V to the solenoid. The ECM changes the energizing time of the solenoid (duty cycle) in accordance with the camshaft position, crankshaft position, throttle position, etc.

Scheme 198

HINT

These DTCs relate to the camshaft timing oil control valve.

MONITOR DESCRIPTION

These DTCs are designed to detect opens or shorts in the camshaft timing oil control valve circuit. If the camshaft timing oil control valve duty cycle is excessively high or low while the engine is running, the ECM will illuminate the MIL and store the DTC.

The VVT system includes the ECM, camshaft timing oil control valve and VVT controller. The ECM sends a target duty cycle control signal to the camshaft timing oil control valve. This control signal regulates the oil pressure supplied to the VVT controller. Camshaft timing control is performed according to engine operating conditions such as the intake air volume, throttle valve position and engine coolant temperature. The ECM controls the camshaft timing oil control valve based on the signals transmitted by several sensors. The VVT controller regulates the intake camshaft angle using oil pressure through the camshaft timing oil control valve. As a result, the relative positions of the camshaft and crankshaft are optimized, the engine torque and fuel economy improve, and the exhaust emissions decrease under overall driving conditions. The ECM detects the actual intake valve timing using signals from the VVT and crankshaft position sensors and performs feedback control. This is how the target intake valve timing is verified by the ECM.

1. The ECM optimizes the intake valve timing using the VVT (Variable Valve Timing) system to control the intake camshaft. The VVT system includes the ECM, camshaft timing oil control valve and VVT controller. The ECM sends a target duty cycle control signal to the camshaft timing oil control valve. This control signal regulates the oil pressure supplied to the VVT controller. The VVT controller can advance or retard the intake camshaft.
2. If the difference between the target and actual intake valve timing is large, and changes in the actual intake valve timing are small, the ECM interprets this as a VVT controller being stuck and stores a DTC.

1. Example
2. A DTC is stored when the following conditions 1 and 2 are met: 1. It takes 5 seconds or more to change the valve timing by 5°CA. 2. After the above condition 1 is met, the camshaft timing oil control valve is forcibly activated for 10 seconds.
3. These DTCs indicate that the VVT controller cannot operate properly due to camshaft timing oil control valve malfunctions or the presence of foreign objects in the camshaft timing oil control valve.

1. These DTCs are designed to detect opens or shorts in the camshaft timing oil control valve circuit. If the camshaft timing oil control valve duty cycle is excessively high or low while the engine is running, the ECM will illuminate the MIL and store the DTC.
2. The VVT (Variable Valve Timing) system adjusts the intake and exhaust valve timing to improve driveability. The engine oil pressure turns the camshaft timing gear to adjust the valve timing. The camshaft timing oil control valve is a solenoid valve and switches the engine oil line. The valve moves when the ECM applies 12 volts to the solenoid. The ECM changes the energizing time of the solenoid (duty cycle) in accordance with the camshaft position, crankshaft position, throttle position, etc.

Scheme 199

These DTCs are designed to detect opens or shorts in the camshaft timing oil control valve circuit. If the camshaft timing oil control valve duty cycle is excessively high or low while the engine is running, the ECM will illuminate the MIL and store the DTC.

HINT

If DTC P0014, P0015, P0024 or P0025 is output, check the VVT (Variable Valve Timing) system.

The Variable Valve Timing (VVT) system includes the ECM, camshaft timing oil control valve and VVT controller. The ECM sends a target duty cycle control signal to the camshaft timing oil control valve. This control signal regulates the oil pressure supplied to the VVT controller. Camshaft timing control is performed according to engine operating conditions such as the intake air volume, throttle valve position and engine coolant temperature. The ECM controls the camshaft timing oil control valve based on the signals transmitted by several sensors. The VVT controller regulates the exhaust camshaft angle using oil pressure through the camshaft timing oil control valve. As a result, the relative positions of the camshaft and crankshaft are optimized, the engine torque and fuel economy improve, and the exhaust emissions decrease under overall driving conditions. The ECM detects the actual exhaust valve timing using signals from the VVT and crankshaft position sensors and performs feedback control. This is how the target exhaust valve timing is verified by the ECM.

1. The ECM optimizes the exhaust valve timing using the VVT (Variable Valve Timing) system to control the exhaust camshaft. The VVT system includes the ECM, camshaft timing oil control valve and VVT controller.
2. The ECM sends a target duty cycle control signal to the camshaft timing oil control valve. This control signal regulates the oil pressure supplied to the VVT controller. The VVT controller can advance or retard the exhaust camshaft. If the difference between the target and actual exhaust valve timing is large, and changes in actual exhaust valve timing are small, the ECM interprets this as a VVT controller being stuck and stores a DTC. Example: A DTC is stored when the following conditions 1 and 2 are met for 10 seconds or more: 1. It takes 5 seconds or more to change the valve timing by 5°CA. 2. After the above condition 1 is met, the camshaft timing oil control valve is forcibly activated during 10 seconds.
3. These DTCs indicate that the VVT controller cannot operate properly due to camshaft timing oil control valve malfunctions or the presence of foreign objects in the camshaft timing oil control valve.

In the VVT (Variable Valve Timing) system, the appropriate intake and exhaust valve open and close timing is controlled by the ECM. The ECM performs intake and exhaust valve control by performing the following: 1) controlling the camshaft and camshaft timing oil control valve, and operating the camshaft timing gear; and 2) changing the relative positions of the camshaft and crankshaft.

To monitor the correlation of the intake camshaft position and crankshaft position, the ECM checks the VVT learned value while the engine is idling. The VVT learned value is calibrated based on the camshaft position and crankshaft position. The intake valve timing is set to the most retarded angle while the engine is idling. If the VVT learned value is out of the specified range in consecutive driving cycles, the ECM illuminates the MIL and stores DTC P0016 (Bank 1) or P0018 (Bank 2).

To monitor the correlation of the exhaust camshaft position and crankshaft position, the ECM checks the VVT learned value while the engine is idling. The VVT learned value is calibrated based on the camshaft position and crankshaft position. The exhaust valve timing is set to the most advanced angle while the engine is idling. If the VVT learned value is out of the specified range in consecutive driving cycles, the ECM illuminates the MIL and stores DTC P0017 (Bank 1) or P0019 (Bank 2).

Refer to DTC P2195. Refer to DESCRIPTION .

HINT

Scheme 200

1. Although the DTC titles say oxygen sensor, these DTCs relate to the air fuel ratio sensor.
2. Sensor 1 refers to the sensor mounted in front of the Three-way Catalytic Converter (TWC) and located near the engine assembly.
3. When one of these DTCs is stored, the ECM enters fail-safe mode. The ECM turns off the air fuel ratio sensor heater in fail-safe mode. The ECM continues operating in fail-safe mode until the engine switch is turned off.
4. The ECM provides a pulse-width modulated control circuit to adjust the current through the heater. The air fuel ratio sensor heater circuit uses a relay on the +B side of the circuit.

The ECM uses information from the air fuel ratio sensor to regulate the air-fuel ratio and keep it close to the stoichiometric level. This maximizes the ability of the Three-way Catalytic Converter (TWC) to purify the exhaust gases.

The air fuel ratio sensor detects oxygen levels in the exhaust gas and transmits the information to the ECM. The inner surface of the sensor element is exposed to the outside air. The outer surface of the sensor element is exposed to the 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 between the exhaust gas and outside air. The platinum coating amplifies this voltage generation.

The air fuel ratio sensor is more efficient when heated. When the exhaust gas temperature is low, the sensor cannot generate useful voltage signals without supplementary heating. The ECM regulates the supplementary heating using a duty cycle approach to adjust the average current in the sensor heater element. If the heater current is outside the normal range, the signal transmitted by the air fuel ratio sensor becomes inaccurate. As a result, the ECM is unable to regulate the air-fuel ratio properly.

When the current in the air fuel ratio sensor heater is outside the normal operating range, the ECM interprets this as a malfunction in the sensor heater and stores a DTC.

1. Refer to DTC P0136. Refer to «DESCRIPTION»(ref-524266-S16469786522013012800000) .

HINT

Scheme 201

1. When any of these DTCs are stored, the ECM enters fail-safe mode. The ECM turns off the heated oxygen sensor heater in fail-safe mode. The ECM continues operating in fail-safe mode until the engine switch is turned off.
2. The ECM provides a pulse-width modulated control circuit to adjust the current through the heater. The heated oxygen sensor heater circuit uses a relay on the +B side of the circuit.

The sensing portion of the heated oxygen sensor has a zirconia element which is used to detect the oxygen concentration in the exhaust gas. If the zirconia element is at the appropriate temperature and the difference between the oxygen concentrations surrounding the inside and outside surfaces of the sensor is large, the zirconia element generates voltage signals. In order to increase the oxygen concentration detecting capacity of the zirconia element, the ECM supplements the heat from the exhaust with heat from a heating element inside the sensor.

Heated oxygen sensor heater range check (P0037, P0038, P0057, P0058, P102D and P105D)

The ECM monitors the current applied to the heated oxygen sensor heater to check the heater for malfunctions.

If the heater current is outside the normal range, the signal transmitted by the heated oxygen sensor becomes inaccurate. When the current in the heated oxygen sensor heater is outside the normal operating range, the ECM interprets this as a malfunction in the sensor heater and stores a DTC.

Heated oxygen sensor heater performance (P0141 and P0161)

After the accumulated heater ON time exceeds 100 seconds, the ECM calculates the heater resistance using the battery voltage and the current applied to the heater.

If the resistance is above the threshold value, the ECM determines that there is a malfunction in the heated oxygen sensor heater and stores DTC P0141 or P0161.

HINT

Normally, the heated oxygen sensor current is 0.4 to 1 A (when the engine is idling, the heated oxygen sensor is warmed up and battery voltage is 11 to 14 V).

The MIL illuminates when irregular intake manifold pressure is detected due to an intake leak.

HINT

When the DTC is stored, the following fail-safe operations occur

1. Idle up is performed.
2. VVT operation is stopped.
3. Updating the A/F learned value is prohibited.
4. Fuel cut is prohibited.
5. ISC flow rate is increased (ISC feedback is stopped).

Refer to DTC P0102. Refer to DESCRIPTION .

The mass air flow meter is a sensor that measures the amount of air flowing through the throttle valve. The ECM uses this information to determine the fuel injection time and to provide an appropriate air-fuel ratio. Inside the mass air flow meter, there is a heated platinum wire which is exposed to the flow of intake air. By applying a specific electrical current to the wire, the ECM heats it to a specific temperature. The flow of incoming air cools both the wire and an internal thermistor, affecting their resistance. To maintain a constant current value, the ECM varies the voltage applied to the wire and internal thermistor. The voltage level is proportional to the airflow through the sensor and the ECM uses it to calculate the intake air volume.

The ECM monitors the average engine load value ratio to check the mass air flow meter for malfunctions. The average engine load value ratio is obtained by comparing the average engine load calculated from the mass air flow meter output to the average engine load estimated from the driving conditions, such as the engine speed and throttle valve opening angle. If the average engine load value ratio is below the threshold value, the ECM determines that the intake air volume is low, and if the average engine load value ratio is above the threshold value, the ECM determines that the intake air volume is high.

If this is detected in 2 consecutive driving cycles, the MIL is illuminated and a DTC is stored.

The mass air flow meter is a sensor that measures the amount of air flowing through the throttle valve.

The ECM uses this information to determine the fuel injection time and to provide the appropriate air-fuel ratio.

Inside the mass air flow meter, there is a heated platinum wire which is exposed to the flow of intake air.

By applying a specific electrical current to the wire, the ECM heats it to a given temperature. The flow of incoming air cools both the wire and an internal thermistor, affecting their resistance. To maintain a constant current value, the ECM varies the voltage applied to the wire and internal thermistor. The voltage level is proportional to the airflow through the sensor, and the ECM uses it to calculate the intake air volume.

The circuit is constructed so that the platinum hot wire and temperature sensor create a bridge circuit, and the power transistor is controlled so that the potentials of A and B remain equal to maintain the predetermined temperature.

HINT

When either of these DTCs is stored, the ECM enters fail-safe mode. During fail-safe mode, the ignition timing is calculated by the ECM according to the engine speed and throttle valve position. The ECM continues operating in fail-safe mode until a pass condition is detected.

Scheme 202

HINT

When either of these DTCs is stored, check the air flow rate by entering the following menus: Powertrain / Engine and ECT / Data List / All Data / MAF.

If there is a defect in the mass air flow meter or an open or short circuit, the voltage level deviates from the normal operating range. The ECM interprets this deviation as a malfunction in the mass air flow meter and stores a DTC.

Example

When the sensor output voltage remains at below 0.2 V, or higher than 4.9 V for more than 3 seconds, the ECM stores a DTC.

If the malfunction is not repaired successfully, a DTC is stored 3 seconds after the engine is next started.

The manifold absolute pressure sensor detects the intake manifold pressure as a voltage using a built-in sensor unit.

Scheme 203

HINT

When either of these DTCs is output, check the manifold absolute pressure using the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / MAP.

The ECM monitors the sensor voltage and uses this value to calculate the manifold absolute pressure. When the sensor output voltage deviates from the normal operating range, the ECM interprets this as a malfunction in the manifold pressure sensor and stores a DTC.

Example

When the sensor output voltage remains below 0.5 V, or higher than 4.5 V for more than 0.5 seconds, the ECM stores a DTC.

If the malfunction is not repaired successfully, a DTC is stored 0.5 seconds after the engine is next started.

The ECM performs OBD II monitoring based on the values from the intake air temperature sensor. If there is no change of the sensor value within the normal range, the ECM will not be able to perform OBD II monitoring or will misdiagnose that there is a malfunction in the sensor. The ECM detects when the intake air temperature sensor value is stuck by performing monitoring after the engine switch is turned off or the engine is started (short soak or long soak).

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 malfunction in the intake air temperature sensor and stores a DTC.

Example

If the sensor output voltage is higher than 4.91 V for 0.5 seconds or more, the ECM determines that there is an open in the intake air temperature sensor circuit and stores DTC P0113. Conversely, if the output voltage is below 0.18 V for 0.5 seconds or more, the ECM determines that there is a short in the sensor circuit and stores DTC P0112.

If the malfunction is not repaired successfully, a DTC is stored 0.5 seconds after the engine is next started.

A thermistor, whose resistance value varies according to the engine coolant temperature, is built into the engine coolant temperature sensor.

The structure of the sensor and its connection to the ECM are the same as those of the intake air temperature sensor.

HINT

When DTC P0115, P0117 or P0118 is stored, the ECM enters fail-safe mode. During fail-safe mode, the engine coolant temperature is estimated to be 80°C (176°F) by the ECM. The ECM continues operating in fail-safe mode until a pass condition is detected.

HINT

When any of these DTCs are stored, check the engine coolant temperature by entering the following menus: Powertrain / Engine and ECT / Data List / All Data / Coolant Temp.

The engine coolant temperature sensor is used to monitor the engine coolant temperature. The engine coolant temperature sensor has a thermistor with a resistance that varies according to 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. These variations in resistance are reflected in the output voltage 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 engine coolant temperature sensor and stores a DTC.

Example

If the sensor output voltage is higher than 4.91 V for 0.5 seconds or more, the ECM determines that there is an open in the engine coolant temperature sensor circuit and stores DTC P0118. Conversely, if the voltage output is below 0.14 V for 0.5 seconds or more, the ECM determines that there is a short in the sensor circuit and stores DTC P0117.

If the malfunction is not repaired successfully, a DTC is stored 0.5 seconds after the engine is next started.

Refer to DTC P0115. Refer to DESCRIPTION .

Engine coolant temperature sensor cold start monitor

When a cold engine start is performed and then the engine is warmed up, if the engine coolant temperature sensor value does not change, it is determined that a malfunction has occurred. If this is detected in 2 consecutive driving cycles, the MIL is illuminated and a DTC is stored.

Engine coolant temperature sensor soak monitor

If the engine coolant temperature sensor value does not change after the warmed up engine is stopped and then the next cold engine start is performed, it is determined that a malfunction has occurred. If this is detected in 2 consecutive driving cycles, the MIL is illuminated and a DTC is stored.

The engine has two temperature sensors, an engine coolant temperature sensor and an intake air temperature sensor, to detect temperature while the engine is in operation. A thermistor, whose resistance value varies according to temperature, is built into each sensor. When the temperature is low, the resistance of the thermistor increases. When the temperature is high, the resistance drops. These variations in resistance are transmitted to the ECM as voltage changes. Based on these temperature signals output from the sensors, the ECM determines the fuel injection time and ignition timing to control the engine.

Scheme 204

HINT

1. Waiting is required to prevent the temperature of the engine from affecting the readings. If the engine has been operated recently, it will not be possible to accurately compare the readings.

1. For diagnosis, in order to duplicate the detection conditions of the DTC, it is necessary to park and leave the vehicle for 7 hours. Leaving the vehicle for 7 hours ensures that the actual engine coolant temperature and intake air temperature are very similar. When the vehicle has been left for less than 7 hours, differences in the readings may exist. However, this does not necessarily indicate a fault.

The ECM monitors the difference between the engine coolant temperature and intake air temperature when the engine is started cold to detect the engine temperature conditions accurately. The monitor runs when the engine is started cold after 7 hours or more have elapsed since the engine was stopped (engine switch turned off) on the previous trip. If the result of (engine coolant temperature - intake air temperature) is outside of the range of -20 to 25°C (-36 to 45°F), the ECM interprets this as a malfunction in the engine coolant temperature and/or intake air temperature sensor circuit, and stores the DTC.

The throttle position sensor is mounted on the throttle body and detects the opening angle of the throttle valve. This sensor is a non-contact type. It uses Hall-effect elements in order to yield accurate signals even in extreme driving conditions, such as at high speeds as well as very low speeds.

The throttle position sensor has 2 sensor circuits, each of which transmits a signal, VTA1 and VTA2. VTA1 is used to detect the throttle valve angle and VTA2 is used to detect malfunctions in VTA1. The sensor signal voltages vary between 0 V and 5 V in proportion to the throttle valve opening angle, and are transmitted to the VTA terminals of the ECM.

As the valve closes, the sensor output voltage decreases and as the valve opens, the sensor output voltage increases. The ECM calculates the throttle valve opening angle according to these signals and controls the throttle actuator in response to driver inputs. These signals are also used in calculations such as air-fuel ratio correction, power increase correction and fuel-cut control.

Scheme 205

HINT

1. When any of these DTCs are stored, check the throttle valve opening angle by entering the following menus: Powertrain / Engine and ECT / Data List / All Data / Throttle Position No. 1 and Throttle Position No. 2.

1. Throttle Position No. 1 is the VTA1 signal, and Throttle Position No. 2 is the VTA2 signal. Reference (Normal Condition) Techstream Display Accelerator Pedal Fully Released Accelerator Pedal Fully Depressed Throttle Position No. 1 0.5 to 1.1 V 3.2 to 4.8 V Throttle Position No. 2 2.1 to 3.1 V 4.6 to 5.0 V

The ECM uses the throttle position sensor to monitor the throttle valve opening angle. There are several checks that the ECM performs to confirm that the throttle position sensor is operating properly.

P0120, P0122, P0123, P0220, P0222, P0223 and P2135

1. A specific voltage difference is expected between the sensor terminals, VTA1 and VTA2, for each throttle valve opening angle. If the difference between VTA1 and VTA2 is incorrect, the ECM interprets this as a malfunction in the sensor and stores a DTC.
2. VTA1 and VTA2 each have a specific voltage range. If VTA1 or VTA2 is outside the normal operating range, the ECM interprets this as a malfunction in the sensor and stores a DTC.
3. VTA1 and VTA2 should never be close to the same voltage level. If VTA1 is within 0.02 V of VTA2, the ECM determines that there is a short circuit in the sensor and stores a DTC.

If the malfunction is not repaired successfully, a DTC is stored 10 seconds after the engine is next started.

P0121

1. This sensor transmits two signals: VTA1 and VTA2. VTA1 is used to detect the throttle opening angle and VTA2 is used to detect malfunctions in VTA1. The ECM performs several checks to confirm that the throttle position sensor and VTA1 are operating properly. For each throttle opening angle, a specific voltage difference is expected between the outputs of VTA1 and VTA2. If the output voltage difference between the two signals deviates from the normal operating range, the ECM interprets this as a malfunction of the throttle position sensor. The ECM illuminates the MIL and stores the DTC. If the malfunction is not repaired successfully, the DTC is stored 2 seconds after the engine is next started.

1. Refer to DTC P0115. Refer to «DESCRIPTION»(ref-524266-S00462545022013012800000) . DTC No. DTC Detection Condition Trouble Area P0125 Engine coolant temperature does not reach closed-loop enabling temperature for 20 minutes (this period varies with the engine start engine coolant temperature) (2 trip detection logic). Engine coolant temperature sensor Cooling system Thermostat

The resistance of the engine coolant temperature sensor varies in proportion to the actual engine coolant temperature. The ECM supplies a constant voltage to the sensor and monitors the signal output voltage of the sensor. The signal output voltage varies according to the changing resistance of the sensor. After the engine is started, the engine coolant temperature is monitored through this signal. If the engine coolant temperature sensor indicates that the engine is not yet warm enough for closed-loop fuel control despite a specified period of time having elapsed since the engine was started, the ECM interprets this as a malfunction in the sensor or cooling system and stores the DTC.

Example

The engine coolant temperature is 0°C (32°F) at engine start. After approximately 1 minute of running time, the engine coolant temperature sensor still indicates that the engine is not warm enough to begin closed-loop fuel (air-fuel ratio feedback) control. The ECM interprets this as a malfunction in the sensor or cooling system and stores the DTC.

This DTC is stored when the engine coolant temperature does not reach 75°C (167°F) despite sufficient engine warm up time having elapsed.

Scheme 206

The ECM estimates the engine coolant temperature based on the starting temperature, engine load and engine speed. The ECM then compares the estimated temperature with the actual engine coolant temperature. When the estimated engine coolant temperature reaches 75°C (167°F), the ECM checks the actual engine coolant temperature. If the actual engine coolant temperature is below 75°C (167°F), the ECM interprets this as a malfunction in the thermostat or the engine cooling system and stores the DTC.

In order to obtain a high purification rate of the carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) components in the exhaust gas, a Three-way Catalytic Converter (TWC) is used. For the most efficient use of the Three-way Catalytic Converter (TWC), the air-fuel ratio must be precisely controlled so that it is always close to the stoichiometric air-fuel ratio. For the purpose of helping the ECM to deliver accurate air-fuel ratio control, a heated oxygen sensor is used.

The heated oxygen sensor is located behind the Three-way Catalytic Converter (TWC), and detects the oxygen concentration in the exhaust gas. Since the sensor is integrated with a heater that heats the sensing portion, it is possible to detect the oxygen concentration even when the intake air volume is low (the exhaust gas temperature is low).

When the air-fuel ratio becomes lean, the oxygen concentration in the exhaust gas is rich. The heated oxygen sensor informs the ECM that the post-Three-way Catalytic Converter (TWC) air-fuel ratio is lean (low voltage, i.e. below 0.45 V).

Conversely, when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas becomes lean. The heated oxygen sensor informs the ECM that the post-Three-way Catalytic Converter (TWC) air-fuel ratio is rich (high voltage, i.e. higher than 0.45 V). The heated oxygen sensor has the property of changing its output voltage drastically when the air-fuel ratio is close to the stoichiometric level.

The ECM uses the supplementary information from the heated oxygen sensor to determine whether the air-fuel ratio after the Three-way Catalytic Converter (TWC) is rich or lean, and adjusts the fuel injection time accordingly. Thus, if the heated oxygen sensor is working improperly due to internal malfunctions, the ECM is unable to compensate for deviations in the primary air-fuel ratio control.

Scheme 207

Active Air-fuel Ratio Control

The ECM usually performs air-fuel ratio feedback control so that the air fuel ratio sensor output indicates a near stoichiometric air-fuel ratio. This vehicle includes active air-fuel ratio control in addition to regular air-fuel ratio control. The ECM performs active air-fuel ratio control to detect any deterioration in the Three-way Catalytic Converter (TWC) and heated oxygen sensor malfunctions (refer to the diagram below).

Active air-fuel ratio control is performed for approximately 15 to 20 seconds while driving with a warm engine. During active air-fuel ratio control, the air-fuel ratio is forcibly regulated to become lean or rich by the ECM. If the ECM detects a malfunction, a DTC is stored.

Abnormal Voltage Output of Heated Oxygen Sensor (DTC P0136 and P0156)

While the ECM is performing active air-fuel ratio control, the air-fuel ratio is forcibly regulated to become rich or lean. If the sensor is not functioning properly, the voltage output variation is small. For example, when the HO2 sensor voltage does not increase to more than 0.59 V during active air-fuel ratio control, the ECM determines that the sensor voltage output is abnormal and stores DTCs DTC P0136 or P0156.

Scheme 208

Open in Heated Oxygen Sensor Circuit (DTC P0137 or P0157)

During active air fuel ratio control, the ECM calculates the oxygen storage capacity* of the three-way catalytic converter by forcibly regulating the air fuel ratio to become rich or lean.

If the heated oxygen sensor has an open, or the voltage output of the sensor noticeably decreases, the oxygen storage capacity indicates an extraordinarily high value. Even if the ECM attempts to continue regulating the air-fuel ratio to become rich or lean, the heated oxygen sensor output does not change.

While performing active air fuel ratio control, when the target air fuel ratio is rich and the heated oxygen sensor voltage output is 0.21 V or less (lean), the ECM interprets this as an abnormally low sensor output voltage and stores DTC P0137 or P0157.

HINT

*: The three-way catalytic converter has the capability to store oxygen. The oxygen storage capacity and the emission purification capacity of the three-way catalytic converter are mutually related. The ECM determines whether the catalyst has deteriorated, based on the calculated oxygen storage capacity value. Refer to MONITOR DESCRIPTION .

Scheme 209

High or Low Impedance of Heated Oxygen Sensor (DTC P0136 and P0156 or P0137 and P0157)

Scheme 210

During normal air-fuel ratio feedback control, there are small variations in the exhaust gas oxygen concentration. In order to continuously monitor the slight variations in the heated oxygen sensor signal while the engine is running, the impedance* of the sensor is measured by the ECM. The ECM determines that there is a malfunction in the sensor when the measured impedance deviates from the standard range.

*: The effective resistance in an alternating current electrical circuit.

HINT

1. The impedance cannot be measured using an ohmmeter.
2. DTCs P0136 and P0156 indicate deterioration of the heated oxygen sensor. The ECM stores these DTCs by calculating the impedance of the sensor when the typical enabling conditions are satisfied (2 driving cycles).
3. DTCs P0137 and P0157 indicate an open or short circuit in the heated oxygen sensor (2 driving cycles). The ECM stores these DTCs when the impedance of the sensor exceeds the threshold of 15 kohms.

Extremely High Output Voltage of Heated Oxygen Sensor (DTC P0138 or P0158)

The ECM continuously monitors the heated oxygen sensor output voltage while the engine is running.

DTC P0138 is set if the heated oxygen sensor voltage output is higher than 1.2 V for 10 seconds or more.

Heated Oxygen Sensor Output Voltage During Fuel Cut (DTC P0139 or P0159)

The sensor output voltage drops to below 0.2 V (extremely lean status) immediately when the vehicle decelerates and fuel cut is operating. If the voltage does not drop to below 0.2 V when accumulated intake air mass is more than 15.3 g, or does not drop from 0.35 V to 0.2 V within 1 second, the ECM determines that the sensor response has deteriorated, illuminates the MIL and stores a DTC.

HINT

1. Refer to DTC P2195. Refer to «DESCRIPTION»(ref-524264-S42068433752013012800000) .
2. Sensor 1 refers to the sensor mounted in front of the three-way catalytic converter and located near the engine assembly.

1. *: Calculated by ECM based on the air fuel ratio sensor output.

After the engine is warmed up, the ECM carries out air-fuel ratio feedback control, and maintains the air-fuel ratio at the theoretical level. In addition, after all the preconditions have been met, active air-fuel ratio control is carried out for approximately 10 seconds, and during active air-fuel ratio control, the ECM measures the response of the air fuel ratio sensor by increasing or decreasing a specific injection volume based on the theoretical air-fuel ratio learned during normal air-fuel control. The ECM determines whether there is an air fuel ratio sensor malfunction at the mid-point of active air-fuel ratio control.

If the air fuel ratio sensor's response ability is reduced, DTCs P014C P014D, P014E and P014F are stored.

If the time it takes the air fuel ratio sensor output to change is delayed, DTCs P015A, P015B, P015C and P015D are stored.

Scheme 211

The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim consists of both the short-term and long-term fuel trims.

The short-term fuel trim is fuel compensation that is used to constantly maintain the air-fuel ratio at stoichiometric levels. The signal from the air fuel ratio sensor indicates whether the air-fuel ratio is rich or lean compared to the stoichiometric ratio. This triggers a reduction in the fuel injection volume if the air-fuel ratio is rich and an increase in the fuel injection volume if it is lean.

Factors such as individual engine differences, wear over time and changes in operating environment cause short-term fuel trim to vary from the central value. The long-term fuel trim, which controls overall fuel compensation, compensates for long-term deviations in the fuel trim from the central value caused by the short-term fuel trim compensation.

HINT

1. When DTC P0171 or P0174 is stored, the actual air-fuel ratio is on the lean side. When DTC P0172 or P0175 is stored, the actual air-fuel ratio is on the rich side.
2. If the vehicle runs out of fuel, the air-fuel ratio is lean and DTC P0171 or P0174 may be stored. The MIL is then illuminated.
3. When the total of the short-term and long-term fuel trim values is within the malfunction threshold (and the engine coolant temperature is higher than 75°C [167°F]), the system is functioning normally.

Under closed-loop fuel control, fuel injection volumes that deviate from those estimated by the ECM cause changes in the long-term fuel trim compensation value. The long-term fuel trim is adjusted when there are persistent deviations in the short-term fuel trim values. Deviations from the ECM estimated fuel injection volumes also affect the average fuel trim learning value, which is a combination of the average short-term fuel trim (fuel feedback compensation value) and the average long-term fuel trim (learning value of the air-fuel ratio). If the average fuel trim learning value exceeds the malfunction threshold, the ECM interprets this as a fault in the fuel system and stores a DTC.

Example

If the average fuel trim learning value is +35% or more, or -35% or less, the ECM interprets this as a fuel system malfunction.

Scheme 212

When a malfunction in the fuel pump circuit is detected, DTC P0230 is stored.

The fuel pump circuit consists of the ECM, fuel pump and fuel pump ECU (which operates the fuel pump). Based on the engine output, the ECM determines the fuel pump speed. The speed is then converted to a duty signal and sent to the fuel pump ECU. Based on the signal sent from the ECM, the fuel pump ECU adjusts the fuel pump operation speed among 3 settings. The fuel pump ECU also has a self-diagnosis function. Based on the fuel pump circuit condition, the fuel pump ECU outputs a diagnostic signal (DI) to the ECM, and the ECM determines if there is a malfunction in the fuel pump circuit.

To monitor the fuel pump circuit, the ECM checks the fuel pump control signal (FPC) and diagnostic signal (DI). The FPC voltage varies between approximately 0 V and approximately 12 V (duty signal). Based on the condition of the fuel pump ECU malfunction, the DI voltage varies between approximately 0 V and approximately 12 V. The ECM then compares the variance of the FPC voltage and DI voltage, and determines if the fuel pump circuit is malfunctioning. When the ECM determines that the fuel pump circuit is malfunctioning, a DTC is stored immediately.

Scheme 213

The ECM illuminates the MIL and stores a DTC immediately when either one of the following conditions, which could cause catalyst deterioration, is detected (2 trip detection logic).

1. Within the first 1000 crankshaft revolutions of the engine starting, an excessive misfiring rate (approximately 40 to 60 misfires per 1000 crankshaft revolutions) occurs once.
2. An excessive misfiring rate (approximately 20 to 50 misfires per 1000 crankshaft revolutions) occurs a total of 4 times.

The ECM flashes the MIL immediately when either one of the following conditions, which could cause Three-way Catalytic Converter (TWC) damage, is detected. Also, the ECM stores a DTC when either one of the following conditions is detected (2 trip detection logic).

1. At a high engine speed, a sufficient amount of misfires to damage the catalyst occurring within 200 crankshaft revolutions is detected once.
2. At a normal engine speed, a sufficient amount of misfires to damage the catalyst occurring within 200 crankshaft revolutions is detected 3 times.

A flat-type knock sensor (non-resonant type) has a structure that can detect vibrations between approximately 6 kHz and 15 kHz.

Knock sensors are fitted onto the engine block to detect engine knocking.

Each knock sensor contains a piezoelectric element which generates a voltage when it becomes deformed.

The voltage is generated when the engine block vibrates due to knocking. Any occurrence of engine knocking can be suppressed by delaying the ignition timing.

HINT

When DTC P0327, P0328, P0332, P0333, P032C, P032D, P033C or P033D is stored, the ECM enters fail-safe mode. During fail-safe mode, the ignition timing is delayed to its maximum retardation. The ECM continues operating in fail-safe mode until the engine switch is turned off.

Reference: Inspection using an oscilloscope

Scheme 214

Standard

The knock sensor, located on the cylinder block, detects spark knock. When spark knock occurs, the piezoelectric element of the sensor vibrates. When the ECM detects a 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 seconds, or if the knock sensor output voltage is outside the normal range, the ECM interprets this as a fault in the knock sensor and stores a DTC.

The crankshaft position sensor system consists of a crankshaft angle sensor rotor and Magnetoresistive Element (MRE) type sensor. The crankshaft angle sensor rotor has 34 teeth at 10° intervals (2 teeth are missing for detecting top dead center), and is installed to the rear end of the crankshaft. The crankshaft position sensor generates 34 signals per crankshaft revolution. The ECM uses the G2 signal to distinguish between the cylinders, and uses the NE signal to detect the crankshaft position and engine speed.

Scheme 215

1. Reference: Inspection using an oscilloscope. Standard Tester Connection Tool Setting Condition Specified Condition C28-6 (NE+) - C28-5 (NE-) 5 V/DIV., 20 msec./DIV. Cranking or idling The correct waveform is as shown C28-9 (G2) - C28-10 (G2-) 5 V/DIV., 20 msec./DIV. Cranking or idling The correct waveform is as shown HINT: G2 is the camshaft position sensor signal, and NE is the crankshaft position sensor signal.

If there is no signal from the crankshaft position sensor despite the crankshaft revolving, the ECM interprets this as a malfunction of the sensor.

When the sensor output voltage remains at below 0.3 V, or higher than 4.7 V for more than 4 seconds, the ECM stores a DTC.

The intake camshaft VVT sensor (VV1 and VV2 signal) consists of a magnet and MRE (Magnetoresistive Element).

The intake camshaft has 3 teeth on its outer circumference. When the intake camshaft rotates, changes occur in the air gaps between the 3 teeth and MRE, which affects the magnetic field. As a result, the resistance of the MRE fluctuates. The VVT sensor converts the camshaft rotation data into pulse signals, uses the pulse signals to determine the camshaft angle, and sends the data to the ECM.

The crankshaft angle sensor rotor has 34 teeth. The MRE generates 34 signals for each crankshaft revolution. Based on a combination of the VVT signal and NE signal, the ECM detects the crankshaft angle. Then the ECM uses this data to control fuel injection time and injection timing. Also, based on the NE signal, the ECM detects the engine speed.

Scheme 216

1. Reference: Inspection using an oscilloscope Standard Tester Connection Tool Setting Condition Specified Condition C28-6 (NE+) - C28-5 (NE-) 5 V/DIV. 20 msec./DIV. Cranking or idling The correct waveform is as shown C28-7 (VV1+) - C28-8 (VV1-) 5 V/DIV. 20 msec./DIV. Cranking or idling The correct waveform is as shown C28-12 (VV2+) - C28-11 (VV2-) 5 V/DIV. 20 msec./DIV. Cranking or idling The correct waveform is as shown HINT: VV1 and VV2 are the VVT sensor signals, and NE is the crankshaft position sensor signal.

If no signal is transmitted by the VVT sensor despite the engine running, or the rotations of the camshaft and crankshaft are not synchronized, the ECM interprets this as a malfunction of the sensor.

Also, when the sensor output voltage remains at below 0.3 V, or higher than 4.7 V for more than 4 seconds, the ECM stores a DTC.

HINT

1. These DTCs indicate malfunctions relating to the primary circuit.
2. If DTC P0351 is stored, check the No. 1 ignition coil circuit.
3. If DTC P0352 is stored, check the No. 2 ignition coil circuit.
4. If DTC P0353 is stored, check the No. 3 ignition coil circuit.
5. If DTC P0354 is stored, check the No. 4 ignition coil circuit.
6. If DTC P0355 is stored, check the No. 5 ignition coil circuit.
7. If DTC P0356 is stored, check the No. 6 ignition coil circuit.
8. If DTC P0357 is stored, check the No. 7 ignition coil circuit.
9. If DTC P0358 is stored, check the No. 8 ignition coil circuit.

A Direct Ignition System (DIS) is used on this vehicle.

The DIS is a 1-cylinder ignition system in which each cylinder is ignited by one ignition coil and one spark plug is connected to the end of each secondary wiring. A powerful voltage, generated in the secondary wiring, is applied directly to each spark plug. The sparks of the spark plugs pass from the center electrode to the ground electrodes.

The ECM determines the ignition timing and transmits the ignition (IGT) signals to each cylinder. Using the IGT signal, the ECM turns the power transistor inside the igniter on and off. The power transistor, in turn, switches on and off the current to the primary coil. When the current to the primary coil is cut off, a powerful voltage is generated in the secondary coil. This voltage is applied to the spark plugs, causing them to spark inside the cylinders. As the ECM cuts the current to the primary coil, the igniter sends back an ignition confirmation (IGF) signal to the ECM for each cylinder ignition.

Scheme 217

1. Reference: Inspection using an oscilloscope.
2. Standard Tester Connection Tool Setting Condition Specified Condition C30-24 (IGT1) - C30-12 (E1) 2 V/DIV., 20 msec./DIV. Idling The correct waveform is as shown C29-27 (IGT2) - C30-12 (E1) 2 V/DIV., 20 msec./DIV. Idling The correct waveform is as shown C30-27 (IGT3) - C30-12 (E1) 2 V/DIV., 20 msec./DIV. Idling The correct waveform is as shown C29-26 (IGT4) - C30-12 (E1) 2 V/DIV., 20 msec./DIV. Idling The correct waveform is as shown C29-25 (IGT5) - C30-12 (E1) 2 V/DIV., 20 msec./DIV. Idling The correct waveform is as shown C30-28 (IGT6) - C30-12 (E1) 2 V/DIV., 20 msec./DIV. Idling The correct waveform is as shown C30-26 (IGT7) - C30-12 (E1) 2 V/DIV., 20 msec./DIV. Idling The correct waveform is as shown C30-25 (IGT8) - C30-12 (E1) 2 V/DIV., 20 msec./DIV. Idling The correct waveform is as shown C30-6 (IGF1) - C30-12 (E1) 2 V/DIV., 20 msec./DIV. Idling The correct waveform is as shown C31-5 (IGF2) - C30-12 (E1) 2 V/DIV., 20 msec./DIV. Idling The correct waveform is as shown HINT: While cranking or idling the engine, check the waveform between terminals IGT (1 to 8) and E1, and IGF1 or IGF2 and E1 of the ECM connector.

Scheme 218

If the ECM does not receive any IGF signals despite transmitting the IGT signal, it interprets this as a fault in the igniter and stores a DTC.

If the malfunction is not repaired successfully, a DTC is stored 1 second after the engine is next started.

The exhaust camshaft VVT sensor (EV1 and EV2 signals) consists of a magnet and MRE (Magnetoresistive Element).

The exhaust camshaft has 3 teeth on its outer circumference. When the exhaust camshaft rotates, changes occur in the air gaps between the 3 teeth and MRE, which affects the magnetic field. As a result, the resistance of the MRE fluctuates. The VVT sensor converts the exhaust camshaft rotation data into pulse signals, uses the pulse signals to determine the camshaft angle, and sends the data to the ECM.

Scheme 219

1. Reference: Inspection using an oscilloscope Standard Tester Connection Tool Setting Condition Specified Condition C28-6 (NE+) - C28-5 (NE-) 5 V/DIV. 20 msec./DIV. Cranking or idling The correct waveform is as shown C28-13 (EV1+) - C28-14 (EV1-) 5 V/DIV. 20 msec./DIV. Cranking or idling The correct waveform is as shown C28-18 (EV2+) - C28-17 (EV2-) 5 V/DIV. 20 msec./DIV. Cranking or idling The correct waveform is as shown HINT: EV1 and EV2 are the VVT sensor signals, and NE is the crankshaft position sensor signal.

If no signal is transmitted by the VVT sensor despite the engine running, or the rotations of the camshaft and crankshaft are not synchronized, the ECM interprets this as a malfunction of the sensor.

Also, when the sensor output voltage remains at below 0.3 V, or higher than 4.7 V for more than 4 seconds, the ECM stores a DTC.

See also:
• DISASSEMBLY
• ON-VEHICLE INSPECTION - Step 2
• ON-VEHICLE INSPECTION - Step 3
• ON-VEHICLE INSPECTION - Step 3
• REMOVAL
• ON-VEHICLE INSPECTION - Step 2
• ON-VEHICLE INSPECTION - Step 2