Engine Control System (2TR-FE) (Diagnostic Codes P0010-P0420): Overview Toyota 4Runner V

DESCRIPTION

HINT

This DTC relates to the oil control valve.

The Variable Valve Timing (VVT) system includes the ECM, intake camshaft timing oil control valve assembly and VVT controller. The ECM sends a target duty cycle control signal to the intake camshaft timing oil control valve assembly. This control signal regulates the oil pressure applied 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 intake camshaft timing oil control valve assembly based on the signals transmitted by several sensors. The VVT controller regulates the intake camshaft angle using oil pressure through the intake camshaft timing oil control valve assembly. 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 camshaft and crankshaft position sensors and performs feedback control. This is how the target intake valve timing is verified by the ECM.

Scheme 526

MONITOR DESCRIPTION

The ECM optimizes the valve timing using the VVT system to control the intake camshaft. The VVT system includes the ECM, OCV and VVT controller. The ECM sends a target duty cycle control signal to the OCV. This control signal regulates the oil pressure supplied to the VVT controller. The VVT controller can advance or retard the intake camshaft.

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 determines the existence of a malfunction and stores the DTC when the actual duty cycle ratio varies from the target duty cycle ratio.

HINT

If DTC P0011 or P0012 is output, check the Variable Valve Timing (VVT) system.

The VVT system includes the ECM, oil control valve and VVT controller. The ECM sends a target duty cycle control signal to the camshaft timing oil control valve assembly. This control signal regulates the oil pressure applied 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 assembly 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 assembly. 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 camshaft and crankshaft position sensors and performs feedback control. This is how the target intake valve timing is verified by the ECM.

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.

1. Example
2. A DTC is set when the following conditions "A" and "B" are met: It takes 5 seconds or more to change the valve timing by 5°CA (Condition "A"). After the above condition is met, the camshaft timing oil control valve is forcibly activated for 10 seconds (Condition "B").
3. DTC P0011 (Advanced Cam Timing) is subject to 1 trip detection logic.
4. DTC P0012 (Retarded Cam Timing) is subject to 2 trip detection logic.
5. 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.

The Variable Valve Timing (VVT) system controls the intake camshaft and exhaust camshaft to achieve optimal valve timing according to various driving conditions. This control is performed based on the intake air volume, throttle valve position, engine coolant temperature and other engine operating conditions. The ECM controls the camshaft timing oil control valves based on the signals transmitted by several sensors. As a result, the relative positions of the camshafts are optimized, improving engine torque and fuel economy and reducing exhaust emissions. In addition, the ECM detects the actual valve timing based on the signals from the VVT sensors and performs feedback control, achieving optimal valve timing.

1. 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.

1. The ECM optimizes the valve timing by using the VVT (Variable Valve Timing) system to control the intake camshaft. The VVT system includes the ECM, oil control valve and VVT controller. The ECM sends a target duty cycle control signal to the 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. The ECM calibrates the intake valve timing by setting the intake camshaft to the most retarded angle while the engine is idling. The ECM closes the oil control valve to retard the cam. The ECM stores this value as the VVT learned value. When the difference between the target and actual intake valve timings is 5°CA (Crankshaft Angle) or less, the ECM stores it. If the VVT learned value matches the following conditions, the ECM determines the existence of a malfunction in the VVT system and stores the DTC.

1. The VVT learned value is less than 33°CA, or more than 51°CA.
2. The above condition continues for 18 seconds or more.

1. This DTC indicates that the intake camshaft is installed at an incorrect angle toward the crankshaft, caused by factors such as the timing chain having jumped a tooth. This monitor begins to run after the engine has idled for 5 minutes.

Refer to DTC P2195, refer to DESCRIPTION.

HINT

Scheme 527

1. When any 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 ignition switch is turned off.
2. Although the DTC titles say oxygen sensor, these DTCs relate to the air fuel ratio sensor.
3. Sensor 1 refers to the sensor mounted in front of the Three-way Catalytic Converter (TWC) and located near the engine assembly.
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.

HINT

1. Sensor 1 refers to the sensor closest to the engine assembly.
2. Sensor 2 refers to the sensor farthest away from the engine assembly.

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.

Refer to DTC P0136, refer to DESCRIPTION.

HINT

Scheme 528

1. Sensor 2 refers to the sensor mounted behind the Three-way Catalytic Converter (TWC) and located far from the engine assembly.
2. When any of these DTCs is 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 ignition switch is turned off.
3. 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.

HINT

1. Sensor 1 refers to the sensor closest to the engine assembly.
2. Sensor 2 refers to the sensor farthest away from the engine assembly.

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 and P102D)

1. 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.

Refer to DTC P0102, refer to DESCRIPTION.

The MAF 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 MAF 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 MAF meter for malfunctions. The average engine load value ratio is obtained by comparing the average engine load calculated from the MAF 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 air flow 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 any of these DTCs are 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 529

HINT

When any of these DTCs are output, check the air flow rate using the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / MAF.

If there is a defect in the MAF 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 MAF meter and stores a DTC.

Example

When the sensor voltage output remains 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 ECM performs OBD II monitoring based on the values from the intake air temperature sensor. If there is no change in 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 ignition switch is turned off or the engine is started (short soak or long soak).

The intake air temperature sensor, which is built into the mass air flow meter, monitors the intake air temperature. The intake air temperature sensor has a built-in thermistor with a resistance that varies according to the intake air temperature. When the intake air temperature becomes low, the resistance of the thermistor increases. When the temperature becomes high, the resistance drops. The intake air temperature sensor is powered by a 5 V supply from terminal THA of the ECM via resistor R. Since resistor R and the intake air temperature sensor are connected in series, when the resistance of the intake air temperature sensor changes depending on the intake air temperature, the voltage at terminal THA also varies accordingly. Based on this signal, the ECM increases the fuel injection volume when the engine is cold to improve driveability.

HINT

When any of these DTCs are output, check the intake air temperature using the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / Intake Air.

The ECM monitors the sensor voltage and uses this value to calculate the intake air temperature. When the sensor output voltage deviates from the normal operating range, the ECM interprets this as a fault in the IAT sensor and stores a DTC.

Example

If the sensor voltage output is higher than 4.91 V for 0.5 seconds or more, the ECM determines that there is an open in the IAT sensor circuit and stores DTC P0113. Conversely, if the voltage output 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 connection between the engine coolant temperature sensor and the ECM is the same as that of the intake air temperature sensor.

HINT

When any of these DTCs are output, check the engine coolant temperature using the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / Coolant Temp.

The 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 ECT. When the sensor output voltage deviates from the normal operating range, the ECM interprets this as a fault in the ECT sensor and stores a DTC.

Example

If the sensor voltage output is higher than 4.91 V for 0.5 seconds or more, the ECM determines that there is an open in the ECT 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.

ECT sensor cold start monitor

1. When a cold engine start is performed and then the engine is warmed up, if the ECT 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.

ECT sensor soak monitor

1. If the ECT 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 the temperature while the engine is in operation. A thermistor, whose resistance value varies according to the 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 530

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 ECT and IAT are very similar. When the vehicle has been left for less than 7 hours, differences in the readings may exist, but 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 (ignition switch turned off) on the previous trip. If the difference between the engine coolant temperature and intake air temperature at the cold start is more than 36°C (96°F), the ECM interprets this as a malfunction in the engine coolant temperature sensor circuit or intake air temperature sensor circuit and stores the DTC.

HINT

These DTCs relate to the throttle position sensor.

The throttle position sensor is built into the throttle body with motor assembly and detects the opening angle of the throttle valve. This sensor is a non-contact type sensor. 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 531

HINT

1. When any of these DTCs are output, check the throttle valve opening angle using the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / ETCS / Throttle Position No. 1 and Throttle Position No. 2.
2. Throttle Position No. 1 is the VTA1 signal, and Throttle Position No. 2 is the VTA2 signal.

REFERENCE (NORMAL CONDITION)

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. The ECM uses the throttle position sensor to monitor the throttle valve opening angle. 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.
2. If the malfunction is not repaired successfully, the DTC is stored 2 seconds after the engine is next started.

Refer to DTC P0115, refer to DESCRIPTION.

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 output signal voltage of the sensor. The output signal 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 70°C (158°F) despite sufficient engine warm up time having elapsed.

Scheme 532

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 70°C (158°F), the ECM checks the actual engine coolant temperature. If the actual engine coolant temperature is below 70°C (158°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 is used. For the most efficient use of the three-way catalytic converter, 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, 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-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 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 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 533

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 and heated oxygen sensor (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, one of the following DTCs is stored: DTC P0136 (abnormal voltage output), P0137 (open circuit), P0138 (short circuit) or P0139.

Abnormal Voltage Output of Heated Oxygen Sensor (DTC P0136)

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 heated oxygen sensor voltage does not decrease to below 0.21 V and does not increase to higher than 0.59 V during active air-fuel ratio control, the ECM determines that the sensor voltage output is abnormal and stores DTC P0136.

Scheme 534

Open or Short in Heated Oxygen Sensor Circuit (DTC P0137 or P0138)

During active air-fuel ratio control, the ECM calculates the Oxygen Storage Capacity (OSC)* 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 short circuit, or the voltage output of the sensor decreases significantly, the OSC is indicated as having an abnormally 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. When the target air-fuel ratio is lean and the voltage output is 0.59 V or higher (rich) during active air-fuel ratio control, the ECM determines that the sensor voltage output is abnormally high and stores DTC P0138.

HINT

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

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

Scheme 535

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

Scheme 536

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. DTC P0136 indicates deterioration of the heated oxygen sensor. The ECM stores this DTC by calculating the impedance of the sensor when the typical enabling conditions are satisfied (2 driving cycles).
3. DTC P0137 indicates an open or short circuit in the heated oxygen sensor (2 driving cycles). The ECM stores this DTC when the impedance of the sensor exceeds the threshold of 15 kohms.

Heated Oxygen Sensor Output Voltage during Fuel Cut (P0139)

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 for 7 seconds or more, or voltage does not drop from 0.35 V to 0.2 V for 1 second, the ECM determines that the sensor response has deteriorated, illuminates the MIL and stores a DTC.

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 is set, the actual air fuel ratio is on the lean side. When DTC P0172 is set, 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 may be set. 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 more 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's 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 thresholds, the ECM interprets this as a fault in the fuel system and sets a DTC.

Example

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

Scheme 537

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 between 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 538

The ECM illuminates the MIL and stores a DTC 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 after the engine starts, an excessive number of misfires (approximately 20 to 50 misfires per 1000 crankshaft revolutions) occurs once.
2. An excessive number of misfires (approximately 20 to 50 misfires per 1000 crankshaft revolutions) occurs a total of 4 times.

The ECM flashes the MIL and stores a DTC when either one of the following conditions, which could cause damage to the three-way catalytic converter, is detected (2 trip detection logic).

1. At a high engine speed, catalyst-damaging misfire, which is monitored every 200 crankshaft revolutions, occurs once.
2. At a normal engine speed, catalyst-damaging misfire, which is monitored every 200 crankshaft revolutions, occurs 3 times. HINT: If catalyst-damaging misfire occurs, the ECM informs the driver by flashing the MIL.

Flat-type knock sensors (non-resonant type) have structures that can detect vibrations between approximately 6 kHz and 15 kHz.

The knock sensor is fitted onto the engine block to detect engine knocking.

The 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 or P0328 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 ignition switch is turned off.

Reference: Inspection using an oscilloscope

Scheme 539

The correct waveform is as shown.

If the output voltage transmitted by the knock sensor remains low or high for more than 1 second, the ECM interprets this as a malfunction in the sensor circuit and stores a DTC.

The monitor for DTCs P0327 and P0328 begins to run when 5 seconds have elapsed since the engine was started.

If the malfunction is not repaired successfully, DTC P0327 or P0328 is stored 5 seconds after the engine is next started.

The crankshaft position sensor system consists of a crankshaft position sensor plate and pickup coil. The sensor plate has 34 teeth, with 2 teeth missing for detecting TDC, and is installed on the crankshaft. The crankshaft position sensor generates 34 signals per crankshaft revolution. The ECM determines the cylinder status based on the G2 signals and detects the crankshaft angle and engine speed from the NE signals.

Scheme 540

1. Reference: Inspection using an oscilloscope HINT: The correct waveforms are as shown. G2 is the camshaft position sensor signal, and NE+ is the crankshaft position sensor signal. Grounding failure of the shielded wire may cause noise in the waveforms. Item Content ECM Terminal Name CH1: G2 - NE- CH2: NE - NE- Tester Range 5 V/DIV. 20 ms./DIV. Condition Idling with warm engine

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

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

The camshaft position sensor consists of a magnet and an iron core which is wrapped with copper wire, and is installed to the cylinder head. When the camshaft rotates, each of the 3 teeth on the camshaft passes by the camshaft position sensor. This activates the internal magnet in the sensor, generating a voltage in the copper wire. The camshaft rotation is synchronized with the crankshaft rotation. When the crankshaft turns twice, voltage is generated 3 times in the camshaft position sensor. The generated voltage in the sensor acts as a signal, allowing the ECM to determine the camshaft position. This signal is then used to control the ignition timing, fuel injection timing and VVT system.

HINT

DTC P0340 indicates a malfunction relating to the camshaft position sensor circuit (the wire harness between the ECM and camshaft position sensor, or the camshaft position sensor itself).

Reference: Inspection using an oscilloscope

HINT

1. The correct waveforms are as shown in the illustration.
2. G2+ is the camshaft position sensor signal, and NE+ is the crankshaft position sensor signal.
3. Grounding failure of the shielded wire may cause noise in the waveforms.

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

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

A Direct Ignition System (DIS) is used on this vehicle to enhance ignition accuracy and suppress high voltage losses.

The DIS is an ignition system in which each cylinder is ignited by one ignition coil assembly. The ECM determines the ignition timing and transmits the ignition (IGT) signals to each cylinder. Based on the IGT signals, the ECM turns the power transistor inside the igniter on and off, turning the current to the primary coil on and off. When the current to the primary coil is cut off, a voltage is generated in the secondary coil and then applied to the spark plugs, causing them to spark inside the cylinders. At the same time, the igniter sends back the ignition confirmation (IGF) signal to the ECM.

Scheme 541

Scheme 542

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 Secondary Air Injection (AIR) system consists of an air pump, the air switching valve, a pressure sensor, the air injection control driver and the ECM. For a short time after a cold engine start, the AIR system pumps secondary air to the exhaust port of the cylinder head to purify the exhaust emissions. The secondary air is supplied by the air pump and is pumped to the exhaust port through the air switching valve assembly.

The air injection control driver drives the air switching valve assembly and air pump according to command signals transmitted by the ECM. The pressure sensor detects the pressure in the secondary air passage when the AIR system is on and off, and transmits a pressure signal to the ECM.

The air injection control driver is not only equipped to drive the pump and valve, but also has a diagnosis function to detect malfunctions in the AIR system circuit.

HINT

As a large current is required to drive the air pump and air switching valve assembly, an air injection control driver is included in this system.

Scheme 543

The air injection control driver detects open and short circuits according to the voltages of the air pump terminal (VP) and air switching valve terminal (VV), and transmits diagnostic information as a signal to the ECM.

For a short time after a cold engine start, the ECM transmits command signals to the air injection control driver to drive the air pump and air switching valve assembly.

The air injection control driver transmits an air switching valve assembly malfunction signal to the ECM if either of the following conditions is met

1. The voltage at the air injection control driver terminal relating to the air switching valve assembly is low despite the air injection control driver receiving command signals from the ECM to drive the air switching valve assembly.
2. The voltage at the air injection control driver terminal relating to the air switching valve assembly is high despite the air injection control driver receiving no command signals from the ECM to drive the air switching valve assembly.

The ECM stores the DTC based on diagnostic signals from the air injection control driver.

Refer to DTC P0412, refer to DESCRIPTION.

The air injection control driver detects open and short circuits according to the voltages of the air pump terminal (VP) and air switching valve terminal (VV), and transmits diagnostic information as a signal to the ECM.

For a short time after a cold engine start, the ECM transmits command signals to the air injection control driver to drive the air pump and air switching valve assembly.

The air injection control driver transmits an air pump malfunction signal to the ECM if either of the following conditions is met

1. The voltage at the air injection control driver terminal relating to the air pump is low despite the air injection control driver receiving command signals from the ECM to drive the air pump.
2. The voltage at the air injection control driver terminal relating to the air pump is high despite the air injection control driver receiving no command signals from the ECM to drive the air pump.

The ECM stores the DTC based on diagnostic signals from the air injection control driver.

The ECM uses sensors mounted in front of and behind the three-way catalytic converter to monitor its efficiency.

The first sensor, the air fuel ratio sensor, sends pre-catalyst information to the ECM. The second sensor, the heated oxygen sensor, sends post-catalyst information to the ECM.

In order to detect any deterioration in the three-way catalytic converter, the ECM calculates the Oxygen Storage Capacity (OSC) of the three-way catalytic converter. This calculation is based on the voltage output of the heated oxygen sensor while performing active air- fuel ratio control, rather than the conventional detecting method, which uses the locus ratio.

The OSC value is an indication of the oxygen storage capacity of the three-way catalytic converter. When the vehicle is being driven with a warm engine, active air-fuel ratio control is performed for approximately 15 to 20 seconds. When it is performed, the ECM deliberately sets the air-fuel ratio to lean or rich levels. If a rich-lean cycle of the heated oxygen sensor is long, the OSC becomes greater. There is a direct correlation between the OSCs of the heated oxygen sensor and the three-way catalytic converter.

The ECM uses the OSC value to determine the state of the three-way catalytic converter. If any deterioration has occurred, it illuminates the MIL and stores the DTC.

Scheme 544

TEXT IN ILLUSTRATION

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