MONITOR DESCRIPTION
The ECM uses the Air-Fuel Ratio sensor (A/F sensor) information to regulate the air-fuel ratio close to the stoichiometric ratio. This maximizes the catalytic converter's ability to purify exhaust gases. The sensor detects oxygen levels in the exhaust gas and sends this signal to the ECM.
The inner surface of the sensor element is exposed to outside air. The outer surface of the sensor element is exposed to exhaust gas. The sensor element is made of platinum coated zirconia and includes an integrated heating element. The zirconia element generates a small voltage when there is a large difference in the oxygen concentrations of the exhaust and the outside air. The platinum coating amplifies the voltage generation. When heated, the sensor becomes very efficient. If the temperature of the exhaust is low, the sensor will not generate useful voltage signals without supplemental heating. The ECM regulates the supplemental heating using a duty-cycle approach to regulate the average current in the heater element. If the heater current is out of the normal range, the sensor's output signals will be inaccurate and the ECM cannot regulate the air-fuel ratio properly.
When the heater current is out of the normal operating range, the ECM interprets this as a malfunction and sets a DTC.
The sensing portion of the heated oxygen sensor has a zirconia element which is used to detect oxygen concentration in the exhaust. If the zirconia element is at the proper temperature and difference of the oxygen concentration between the inside and outside surface of sensor is large, the zirconia element will generate voltage signals. In order to increase the oxygen concentration detecting capacity in the zirconia element, the ECM supplements the heat from the exhaust with heat from a heating element inside the sensor. When current in the sensor is out of the standard operating range, the ECM interprets this as a fault in the heated oxygen sensor and sets a DTC.
Example
The ECM will set a high current DTC if the current in the sensor is more than 2.35 A when the heater is OFF. Similarly, the ECM will set a low current DTC if the current is less than 0.2 A when the heater is ON.
If there is a defect in the sensor or an open or short circuit, the voltage level will deviate outside the normal operating range. The ECM interprets this deviation as a defect in the MAF meter and sets a DTC.
Example
When the sensor voltage output is less than 0.2 V or more than 4.9 V and if either condition continues for more than 3 seconds.
The Mass Air Flow (MAF) meter helps the ECM calculate the amount of air flowing through the throttle valve. The ECM uses this information to determine the fuel injection time and provide a proper air fuel ratio. Inside the MAF meter, there is a heated platinum wire exposed to the flow of intake air. By applying a specific current to the wire, the ECM heats this wire to a given temperature. The flow of incoming air cools the wire and an internal thermistor, affecting their resistance. To maintain a constant current value, the ECM varies the voltage applied to these components in the MAF meter. The voltage level is proportional to the air flow through the sensor. The ECM interprets this voltage as the intake air amount. If there is a defect in the sensor or an open or short circuit, the voltage level will deviate outside the normal operating range. The ECM interprets this deviation as a defect in the MAF meter and sets a DTC.
Example
If the voltage is more than 2.2 V at idle or less than 0.4 V at idle off, the ECM interprets this as a defect in the MAF meter and sets a DTC.
Scheme 1
The ECM monitors the sensor voltage and uses this value to calculate the intake air temperature. When the sensor output voltage deviates from the normal operating range, the ECM interprets this as a fault in the IAT sensor and sets a DTC.
Example
When the sensor voltage output equal to -40°C (-40°F), or more than 140°C (284°F).
The Engine Coolant temperature (ECT) sensor is used to monitor the ECT. 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 sets a DTC.
Example
When the ECM calculates that the ECT is -40°C (-40°F) or more than 140°C (284°F) and if either condition continues 0.5 seconds or more, the ECM will set a DTC.
The Engine Coolant Temperature (ECT) sensor is used to monitor the ECT. 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 sets a DTC.
Examples
- Upon starting the engine, the ECT is between 35°C (95°F) and 60°C (140°F). If, after driving for 250 seconds, the ECT still remains within 3°C (5.4°F) of the starting temperature, a DTC will be set. (2 trip detection logic)
- Upon starting the engine, the ECT is over 60°C (140°F). If, after driving for 250 seconds, the ECT still remains within 1°C (1.8°F) of the starting temperature, a DTC will be set (6 trip detection logic).
The ECM uses the throttle position sensor to monitor the throttle valve opening angle.
- If the difference between VTA and VTA2 is incorrect, the ECM interprets this as a default and will set a DTC.
- VTA and VTA2 have their own specific voltage operating range. If VTA or VTA2 is out of the normal operating range, the ECM interprets this as a fault and will set a DTC.
- VTA and VTA2 each have a specific voltage operating range. If VTA or VTA2 is out of the normal operating range, the ECM interprets this as a fault and will set a DTC.
- VTA and VTA2 should never be close to the same voltage levels. If VTA is within 0.02V of VTA2, the ECM interprets this as a short circuit in the throttle position sensor system and will set a DTC.
The ECM uses the throttle position sensor to monitor the throttle valve opening angle.
This sensor includes 2 signals: VTA and VTA2. VTA is used to detect the throttle opening angle and VTA2 is used to detect malfunctions in VTA. There are several checks that the ECM performs confirm proper operation of the throttle position sensor and VTA.
There is a specific voltage difference expected between VTA and VTA2 for each throttle opening angle. If the voltage output difference of the VTA and VTA2 deviates from the normal operating range, the ECM interprets this as a malfunction of the throttle position sensor. The ECM will turn on the MIL and a DTC is set.
The ECM monitors the ECT signal voltage after engine start-up. If, after sufficient time has passed, the sensor still reports that the engine is not warm enough for closed-loop fuel control, the ECM interprets this as a fault in the sensor or cooling system and sets a DTC.
Example
The ECT is 0°C (32°F) at engine start. After 5 minutes running time, the ECT sensor still indicates that the engine is not warm enough to begin air fuel ratio feedback control of the air-fuel ratio. The ECM interprets this as a fault in the sensor or cooling system and will set a DTC.
The ECM monitors the rear heated oxygen sensor (HO2S) in the following 2 items
- The HO2S voltage changes between Rich (more than 0.45 volts) and Lean (less than 0.45 volts) while the vehicle is running (repeating acceleration and deceleration). If not, the ECM interprets this as a malfunction, illuminates the MIL, and then sets DTC.
- The HO2S voltage does not remain at less than 0.05 volts for a long time while the vehicle is running. If it does, the ECM interprets this as a malfunction, illuminates the MIL, and then sets DTC.
The knock sensor, located on the cylinder block, detects spark knock. When a spark knock occurs, the sensor picks-up vibrates in a specific frequency range. When the ECM detects the voltage in this frequency range, it retards the ignition timing to suppress the spark knock.
The ECM also senses background engine noise with the knock sensor and uses this noise to check for faults in the sensor. If the knock sensor signal level is too low for more than 10 seconds, and if the knock sensor output voltage is out of normal range, the ECM interprets this as a fault in the knock sensor and sets a DTC.
If there is no signal from the crankshaft sensor even though the engine is revolving, the ECM interprets this as a malfunction of the sensor.
If there is no signal from the camshaft position sensor even though the engine is revolving, or if the rotation of the camshaft and the crankshaft is not synchronized, the ECM interprets this as a malfunction of the sensor.
The ECM uses sensors mounted before and after the three-way catalyst (TWC) to monitor its' efficiency. The first sensor, an air fuel ratio sensor (A/F sensor), sends pre-catalyst A/F ratio information to the ECM. The second sensor, a heated oxygen sensor (O2S), sends post-catalyst information to the ECM. The ECM compares these two signals to judge the efficiency of the catalyst and the catalyst's ability to store oxygen. During normal operation, the TWC stores and releases oxygen as needed. The capacity to store oxygen results in a low variation in the post-TWC exhaust stream as shown below.
If the catalyst is functioning normally, the waveform of the heated oxygen sensor slowly switches between RICH and LEAN.
If the catalyst is deteriorated, the waveform will alternate frequently between RICH and LEAN. As the catalyst efficiency degrades, its ability to store oxygen is reduced and the catalyst output becomes more variable. When running the monitor, the ECM compares sensor 1 signals (A/F sensor) over a specific amount of time to determine catalyst efficiency. The ECM begins by calculating the signal length for both sensors (for the rear oxygen sensor, the ECM uses the output voltage signal length).
If the oxygen sensor output voltage signal length is greater than the threshold (threshold is calculated based on the A/F sensor signal length), the ECM concludes that the catalyst is malfunctioning. The ECM will turn on the MIL and a DTC will be set.
Scheme 2
Scheme 3
The ECM tests the Evaporative Emissions (EVAP) system using the fuel tank pressure sensor, the Canister Close Valve (CCV), and the EVAP VSV. The ECM closes the EVAP system and introduces a negative pressure (vacuum) into it. The ECM then monitors the internal pressure using the fuel tank pressure sensor (refer to graphic).
P0441
The EVAP VSV
- Is used to purge the evaporative emissions from the fuel tank into the intake manifold.
- Works with the CCV to create a negative pressure (vacuum) inside the fuel tank, and performs leak tests.
Opening or closing malfunctions in the EVAP VSV prompt the ECM to set DTC P0441.
The ECM checks for a EVAP VSV "stuck closed" fault by commanding the EVAP VSV open with the CCV (vent) closed. The fuel tank should develop a high negative pressure (vacuum). If it does not, the ECM determines that despite an OPEN command, the EVAP VSV remained closed. The ECM turns on the MIL and a DTC is set.
The ECM checks for a EVAP VSV "stuck open" fault by commanding both the EVAP VSV and CCV closed at a time when the fuel tank is at atmospheric pressure. If the fuel tank develops a high negative pressure (vacuum) during this early stage of the test, the ECM determines that the EVAP VSV is stuck open. The ECM will turn on the MIL and DTC is set.
P0446
The CCV is open under normal conditions. The CCV is used to
- After the EVAP VSV purges the evaporative emissions from the fuel tank to the intake manifold, the CCV draws fumes from the fuel tank into the charcoal canister.
- Relieve pressure inside the fuel tank when the pressure has suddenly risen.
- Along with the EVAP VSV, it creates a negative pressure (vacuum) inside the fuel tank and performs leak tests.
The ECM checks for a CCV "stuck closed" malfunction by commanding both valves (EVAP VSV and CCV) open at a time when the fuel tank is at atmospheric pressure. If the fuel tank develops a high negative pressure (vacuum) and it remains in that state for more than 4 seconds, the ECM determines that the CCV (vent) is stuck closed. The ECM will turn on the MIL and a DTC is set. This malfunction is detected regardless of the engine coolant temperature.
The ECM checks for a CCV "stuck open" malfunction by commanding the EVAP VSV open with the CCV closed when the fuel tank should have developed a high negative pressure (vacuum). If the fuel tank did not develop the proper high negative pressure (vacuum), the ECM concludes that the CCV must have been "stuck open". The ECM will turn on the MIL and a DTC is set.
P0442 and P0456
A leak in the evaporative emission system prompts the ECM to set DTC P0442, P0456.
The ECM checks for leaks in the system by introducing a high negative pressure (vacuum) from the intake manifold by commanding the EVAP VSV open while the CCV (vent) is closed. After sufficient time has elapsed the fuel tank should have developed a high negative pressure (vacuum) and the EVAP VSV is closed. The ECM then monitors the pressure-rise (loss of vacuum) in the fuel tank. If the pressure rises too rapidly, the ECM concludes that there is a leak in the system. The ECM will turn on the MIL and a DTC is set.
The ECM has separate DTCs for small and large leaks
- DTC P0442 is set when the internal fuel tank pressure has a large increase and the EVAP system has a small leak.
- DTC P0456 is set when the internal fuel tank pressure increase slightly and the EVAP system has a very small leak.
Scheme 4
Scheme 5
Scheme 6
Scheme 7
Scheme 8
Scheme 9
DTC "P0451, P0452 or P0453" is recorded by the ECM when the vapor pressure sensor malfunctions.
The ECM assumes that the vehicle is being driven when the transmission counter gear indicates more than 300 RPM and over 30 seconds have passed since the park/neutral position switch was turned OFF. If there is no signal from the vehicle speed sensor with these conditions satisfied, the ECM concludes that the vehicle speed sensor is malfunctioning. The ECM will turn on the MIL and a DTC is set.
The ECM regulates the idle speed by opening and closing the throttle valve using the ETCS. The ECM concludes that the idle speed control ECM function is malfunctioning if: 1) the actual idle RPM varies more than remains at the maximum or minimum five times or more during a drive cycle. The ECM will turn on the MIL and set a DTC.
Example
If the actual idle RPM varies from the target idle RPM by more than 200 ( * 1) RPM five times during a drive cycle, the ECM will turn on the MIL and a DTC is set.
* 1: RPM threshold varies with engine load.
Scheme 10
The battery supplies electricity to the ECM even when the ignition switch is OFF. This electricity allows the ECM to store data such as DTC history, freeze frame data, fuel trim values and other data. If the battery voltage falls below a minimum level, the ECM will conclude that there is a fault in the power supply circuit.
The next time the engine starts, the ECM will turn on the MIL and a DTC will be set.
The ECM continuously monitors its internal memory status, internal circuits, and output signals to the throttle actuator. This self-check ensures that the ECM is functioning properly. If any malfunction is detected, the ECM will set the appropriate DTC and illuminate the MIL.
The ECM memory status is diagnosed by internal "mirroring" of the main CPU and the sub CPU to detect random access memory (RAM) errors. The two CPUs also perform continuous mutual monitoring.
The ECM sets a DTC if: 1) outputs from the 2 CPUs are different and deviate from the standards, 2) the signals to the throttle actuator deviate from the standards, 3) a malfunction is found in the throttle actuator supply voltage, and 4) any other ECM malfunction is found.
Scheme 11
While the engine is being cranked, the battery positive voltage is applied to terminal STA of the ECM.If the vehicle is being driven and the ECM detects the starter control signal (STA), the ECM concludes that the starter control circuit is malfunctioning. The ECM will turn on the MIL and a DTC is set.
Scheme 12
This circuit prevents the engine from stalling when the vehicle is suddenly braked while the torque converter is in the lock-up condition. The ECM receives the signal from the stop light switch at the time brake pedal is depressed. Then, the ECM stops sending the "lock-up" command to the lock-up solenoid valve and the torque converter clutch "unlocks". The ECM monitors the brake light switch "B" signal. If the ECM detects that the switch remains ON while the vehicle is in "stop and go" driving conditions * , it will illuminate the MIL and a DTC is set.
The ECM monitors both the throttle motor clutch current and the throttle position sensor to confirm proper operation of the throttle motor and clutch. If the clutch current is out of range, the ECM will interpret this as malfunction of the throttle motor clutch. If the throttle position sensor value does not change when the throttle motor is operated, the ECM will conclude that the throttle motor clutch is "stuck".
If the ECM detects a malfunction in the throttle motor clutch, it will
- Illuminate the MIL and set a DTC.
- Disconnect the electrical supply to the throttle motor.
- Disengage the throttle motor clutch. (With the throttle motor clutch disengaged, the throttle motor is disconnected from the throttle valve).
The throttle motor is operated by the engine control module (ECM) and it opens and closes the throttle valve. The opening angle of the throttle valve is detected by the throttle position sensor. It provides feedback to the ECM to control the throttle motor and the throttle valve opening angle properly in response to driver inputs.
The ECM monitors the current flows through the throttle motor and detects malfunctions and/or an open circuit in the throttle motor based on these measurements. When the current deviates from the normal range, the ECM interprets this as a malfunction in the throttle motor and sets a DTC.
If the ECM determines that the ETCS is malfunctioning, it shuts off the power to the throttle motor, the throttle valve is closed by the return spring, and the throttle valve is locked at a certain operating angle. At the same time, operation of the ECTS is cancelled until the system returns to normal or the ignition switch is turned to OFF.
The throttle motor is operated by the engine control module (ECM) and it opens and closes the throttle valve. The opening angle of the throttle valve is detected by the throttle position sensor. It provides feedback to the ECM to control the throttle motor and the throttle valve opening angle properly in response to driver inputs.
The ECM concludes that there is a malfunction of the electrical throttle control system (ECTS) when the throttle valve remains at a fixed angle although high drive current is supplied from the ECM. The ECM will turn on the malfunction indicator lamp (MIL) and a DTC is set.
The engine control module (ECM) monitors the battery supply voltage applied to the throttle motor. When the power supply voltage drops below the threshold, the ECM concludes that there is an open in the power supply circuit. A DTC is set and the malfunction indicator lamp (MIL) is turned ON.
The throttle motor is operated by the engine control module (ECM) and it opens and closes the throttle valve. The opening angle of the throttle valve is detected by the throttle position sensor. It provides feedback to the ECM to control the throttle motor and the throttle valve opening angle properly in response to driver inputs.
The ECM determines the "actual" throttle angle based on the throttle position sensor signal. The "actual" throttle position is compared to the "target" throttle position commanded by the ECM. If the difference of these two values exceeds a specified limit, the ECM interprets this as a malfunction in the ETCS. The ECM turns on the malfunction indicator lamp (MIL) and a DTC is set.
If the ECM determines that the ETCS is malfunctioning, it shuts off the power to the throttle motor, the throttle valve is closed by the return spring, and the throttle valve is locked at a certain operating angle. At the same time, operation of the ECTS is cancelled until the system returns to normal or the ignition switch is turned OFF.
The accelerator pedal position sensor is equipped with 2 measuring elements: one is for engine control (VPA) and the other is for malfunction detection in the sensor itself (VPA2). These elements vary their resistance according to how much the accelerator pedal is depressed. The ECM applies a regulated reference voltage to the throttle position sensor "+" terminal and calculates the amount of the accelerator pedal depression based on the voltages present at the throttle position sensor "signal" terminals. When the amount of the accelerator pedal depression is small, the output voltages of these elements are low. When it is large, the output voltages are high.
If the ECM detects that the output voltage of the element(s) is out of the normal range, the ECM will determine that the accelerator pedal position sensor is malfunctioning and set a DTC.
Scheme 13
The accelerator pedal position sensor is mounted on the accelerator pedal bracket. The accelerator pedal position sensor has 2 sensor elements / signal output: VPA and VPA2. VPA is used to detect the actual accelerator pedal angle (used for engine control) and VPA2 is used to detect malfunctions in VPA. When the difference between the voltage output of VPA and VPA2 deviates from the standard, the ECM concludes the accelerator pedal position sensor has a malfunction. The ECM turns on the MIL and a DTC is set.
Under the air-fuel ratio feedback control, if the voltage output of the A/F sensor indicates RICH or LEAN for a certain period of time or more, the ECM concludes that there is a fault in the A/F sensor system. The ECM will turn on the MIL and a DTC is set.
Example
If the A/F sensor voltage output is less than 2.8 V (very RICH) for 10 seconds even though voltage output of the heated oxygen sensor output voltage is less than 0.85 V, the ECM sets DTC P2196 or DTC P2198. If the heated oxygen sensor output voltage is 0.15 V or more but the A/F sensor voltage output is more than 3.8 V (very LEAN) 10 seconds, DTC P2195 is set.
During feedback control (while the engine is in closed loop control), if the A/F sensor output is stuck for 30 seconds, the ECM concludes that there is malfunction in the A/F sensor circuit and sets a DTC.