Advanced Diagnostics: Overview Honda Element I

Identifying Variable Valve Timing Control Components. Scheme 249

General Description

The variable valve timing control (VTC) system controls the timing of the intake camshaft. It uses hydraulic pressure to operate the VTC actuator so the valve timing is optimized depending on driving conditions. The engine control module (ECM)/ powertrain control module (PCM) monitors the phase control command and the actual timing of the camshaft by using camshaft position (CMP) sensor A. If the phase difference between them is excessive for a certain time period, a malfunction is detected and a DTC is stored.

The manifold absolute pressure (MAP) sensor senses manifold absolute pressure (vacuum) and converts it into electrical signals. The MAP sensor outputs low signal voltage at high-vacuum (throttle valve closed) and high signal voltage at low-vacuum (throttle valve wide open).

If a signal voltage from the MAP sensor is a set value or less, the engine control module (ECM)/powertrain control module (PCM) detects a malfunction and a DTC is stored.

The manifold absolute pressure (MAP) sensor senses manifold absolute pressure (vacuum) and converts it into electrical signals. The MAP sensor outputs low signal voltage at high-vacuum (throttle valve closed) and high signal voltage at low-vacuum (throttle valve wide open). If a signal voltage from the MAP sensor is a set value or more, the engine control module (ECM)/powertrain control module (PCM) detects a malfunction and a DTC is stored.

Two engine coolant temperature sensors and one intake air temperature sensor are used by the engine control module (ECM)/powertrain control module (PCM).

When the engine is stopped and enough time has passed, the temperature of the engine will equal the ambient temperature. When an inappropriate temperature is detected after comparing the temperature readings of each sensor, a malfunction in the corresponding sensor is detected and a DTC is stored.

The intake air temperature (IAT) sensor is a thermistor that detects intake air temperature, and it is used for A/F feedback control to compensate for the atmospheric density fluctuations that accompany changes in intake air temperature.

The IAT sensor resistance varies depending on temperature. The output voltage and the sensor resistance increase as the intake air temperature decreases. Conversely, the output voltage and the sensor resistance decrease as the intake air temperature increases. If the IAT sensor output voltage is excessively low, the engine control module (ECM)/powertrain control module (PCM) detects a malfunction and a DTC is stored.

The intake air temperature (IAT) sensor is a thermistor that detects intake air temperature, and it is used for A/F feedback control to compensate for the atmospheric density fluctuations that accompany changes in intake air temperature.

The IAT sensor resistance varies depending on temperature. The output voltage and the sensor resistance increase as the intake air temperature decreases. Conversely, the output voltage and the sensor resistance decrease as the intake air temperature increases. If the IAT sensor output voltage is excessively high, the engine control module (ECM)/powertrain control module (PCM) detects a malfunction and a DTC is stored.

The engine control module (ECM)/powertrain control module (PCM) supplies voltage to the engine coolant temperature (ECT) signal circuit (about 5 V) through a pull-up resistor. As the engine coolant cools, ECT sensor resistance increases, and the ECM/PCM detects a high signal voltage. As the engine coolant warms, ECT sensor resistance decreases, and the ECM/PCM detects a low signal voltage.

If the ECT output voltage after driving a set time after starting the engine does not reach a set temperature, or when the difference between the ECT output voltage when driving and the output voltage of the ECT after the engine is stopped a set time does not change a certain amount, a malfunction is detected and a DTC is stored.

The engine control module (ECM)/powertrain control module (PCM) supplies voltage to the engine coolant temperature (ECT) signal circuit (about 5 V) through a pull-up resistor. As the engine coolant cools, the ECT sensor resistance increases, and the ECM/PCM detects a high signal voltage. As the engine coolant warms, the ECT sensor resistance decreases, and the ECM/PCM detects a low signal voltage.

If the ECT output voltage does not reach a specified temperature at which closed-loop control for stoichiometric air/fuel ratio starts within a set time, depending on the initial coolant temperature after starting the engine, the ECM/PCM detects a malfunction and a DTC is stored.

The thermostat is closed when the engine coolant temperature is low, and it stops the circulation of engine coolant to speed engine warm up. When the engine coolant temperature increases, the thermostat opens and circulates engine coolant to control its temperature. When the engine coolant temperature decreases, the opening area of the thermostat is reduced to regulate the engine coolant temperature. If the thermostat sticks open, engine warm up is delayed, and exhaust emissions are adversely affected. The engine control module (ECM)/powertrain control module (PCM) estimates the engine coolant temperature after starting the engine from the initial engine coolant temperature and driving conditions, and compares it with the actual engine coolant temperature that is detected by the engine coolant temperature (ECT) sensor.

If the actual engine coolant temperature is below the estimated engine coolant temperature (when X shown in the graph is large), a thermostat malfunction is detected and a DTC is stored.

The air/fuel ratio (A/F) sensor has a linear signal output in relation to the oxygen concentration. The engine control module (ECM)/powertrain control module (PCM) computes the air/fuel ratio from A/F sensor output voltage and uses the fuel feedback control to improve exhaust emissions. The ECM/PCM measures the inversion cycle of the A/F sensor output voltage during closed loop control of the stoichiometric ratio, detects a deteriorated response, and stores a DTC if the inversion cycle has extended to a specified time period or more.

The air/fuel ratio (A/F) sensor is activated by warming the element with a heater to maintain it at a steady high temperature for accurate air/fuel (A/F) ratio calculation. The A/F sensor does not become active when the element is not properly heated due to a heater malfunction, and the exhaust emissions deteriorate. The engine control module (ECM)/powertrain control module (PCM) monitors the A/F sensor condition by monitoring the A/F sensor internal resistance.

1. When the A/F sensor does not activate in a set time after the A/F sensor heater is turned on (with high A/F sensor internal resistance), a malfunction of the A/F sensor heater is detected, and a DTC is stored.
2. The A/F sensor heater cycles ON and OFF within a set time. The heater's state is detected by monitoring the internal resistance of the A/F sensor. If the resistance remains high when the heater is ON, a malfunction in the A/F sensor heater is detected, and a DTC is stored.

Because the degree of effect on engine control differs according to the A/F sensor internal resistance, there are two malfunction detection threshold levels. When either one is reached, a malfunction is detected.

The secondary heated oxygen sensor (HO2S) (sensor 2) detects the oxygen content in the exhaust gas downstream of the three way catalytic converter (TWC) during stoichiometric air/fuel ratio feedback control based on the air/fuel ratio (A/F) sensor (sensor 1) output voltage. The secondary HO2S controls the air/fuel ratio from the A/F sensor output voltage so that the TWC efficiency is optimized.

After current is applied to the secondary HO2S heater, if the secondary HO2S output continues low (lean) during feedback control, a malfunction is detected and a DTC is stored.

The secondary heated oxygen sensor (HO2S) (sensor 2) detects the oxygen content in the exhaust gas downstream of the three way catalytic converter (TWC) during stoichiometric air/fuel ratio feedback control based on the air/fuel ratio (A/F) sensor (sensor 1) output voltage. The secondary HO2S controls the air/fuel ratio from the A/F sensor output voltage to optimize TWC efficiency.

After current is applied to the secondary HO2S heater, if the secondary HO2S output continues high (rich) exceeding the upper limit used during feedback control, a malfunction is detected and a DTC is stored.

The secondary heated oxygen sensor (HO2S) (sensor 2) detects the oxygen content in the exhaust gas downstream of the three way catalytic converter (TWC) during stoichiometric air/fuel ratio feedback control. The secondary HO2S controls the air/fuel ratio with the A/F sensor output voltage to optimize TWC efficiency.

If the response time of the secondary HO2S becomes longer than the specified time after current to the secondary HO2S heater is applied, a malfunction is detected and a DTC is stored.

A heater for the zirconia element is embedded in the secondary heated oxygen sensor (secondary HO2S), and it is controlled by the engine control module (ECM)/powertrain control module (PCM). When activated, it heats the sensor to stabilize and speed up the detection of oxygen content when the exhaust gas temperature is cold.

If the secondary HO2S heater draws more or less than a specified amperage, the ECM/PCM detects a malfunction and a DTC is stored.

The engine control module (ECM)/powertrain control module (PCM) detects the oxygen content in the exhaust gas from the air/fuel ratio (A/F) sensor (sensor 1) signal voltage, and it performs fuel feedback control to maintain the optimal air/fuel ratio. The air/fuel ratio coefficient for correcting the amount of injected fuel is the short term fuel trim. The ECM/PCM varies short term fuel trim continuously to keep the air/fuel ratio close to the stoichiometric ratio for all driving conditions.

Long term fuel trim is computed from short term fuel trim and is used to regulate long term deviation from the stoichiometric air/fuel ratio, which occurs when fuel metering components deteriorate with age or system failures occur. In addition, long term fuel trim is stored in the ECM/PCM memory and is used to determine when fuel metering components malfunction. When long term fuel trim is higher than normal, which is about 1.0 (0 %), the amount of injected fuel must be increased, and when lower than normal, it must be decreased. If long term fuel trim is higher than normal (too lean), a malfunction in the fuel metering components is detected and a DTC is stored.

The engine control module (ECM)/powertrain control module (PCM) detects the oxygen content in the exhaust gas from the air/fuel ratio (A/F) sensor (sensor 1) signal voltage, and it performs fuel feedback control to maintain the optimal air/fuel ratio. The air/fuel ratio coefficient for correcting the amount of injected fuel is the short term fuel trim. The ECM/PCM varies short term fuel trim continuously to keep the air/fuel ratio close to the stoichiometric ratio for all driving conditions. Long term fuel trim is computed from short term fuel trim and is used to regulate long term deviation from the stoichiometric air/fuel ratio, which occurs when fuel metering components deteriorate with age or system failures occur. In addition, long term fuel trim is stored in the ECM/PCM memory and is used to determine when fuel metering components malfunction. When long term fuel trim is higher than normal, which is about 1.0 (0 %), the amount of injected fuel must be increased, and when lower than normal, it must be decreased. If long term fuel trim is lower than normal (too rich), a malfunction in the fuel metering components is detected and a DTC is stored.

The crankshaft vibrates slightly when each cylinder fires. If a misfire occurs, the crankshaft rotation speed changes rapidly. The engine control module (ECM)/powertrain control module (PCM) monitors the crankshaft rotation speed based on the output pulses from the crankshaft position (CKP) sensor. By monitoring changes in the crankshaft rotation speed, the ECM/PCM counts the number of misfires and determines which cylinder is misfiring. If more than one DTC from P0301 through P0304 has been stored while misfires in multiple cylinders are detected, a malfunction is detected and a DTC is stored.

There are two types of misfire detection.

Type 1 (1 drive cycle): When the number of misfires per 200 engine revolutions reaches the level that damages the three way catalyst (TWC), a DTC is stored and the MIL blinks. When the misfire ceases, the MIL remains on steady instead of blinking.

Type 2 (2 drive cycles): When the number of misfires per 1,000 engine revolutions reaches the level that affects FTP mode exhaust emissions, a DTC is stored and the MIL comes on.

The crankshaft vibrates slightly when each cylinder fires. If a misfire occurs, the crankshaft rotation speed changes rapidly. The engine control module (ECM)/powertrain control module (PCM) monitors engine misfiring based on the output pulses from the crankshaft position (CKP) sensor, counts the number of misfires, and determines which cylinder is misfiring. If a misfire is detected, a DTC is stored.

There are two types of misfire detection.

Type 1 (1 drive cycle): When the number of misfires per 200 engine revolutions reaches the level that damages the three way catalyst (TWC), a DTC is stored and the MIL blinks. When the misfire ceases, the MIL remains on steady instead of blinking.

Type 2 (2 drive cycles): When the number of misfires per 1,000 engine revolutions reaches the level that affects FTP mode exhaust emissions, a DTC is stored and the MIL comes on.

The knock sensor is mounted on the engine block and detects engine knocking. The vibrations caused by the knocking are converted into electrical signals through the piezo ceramic element. The engine control module (ECM)/powertrain control module (PCM) controls the ignition timing based on the electrical signals. If the signals from the knock sensor do not vary for a set time period, the ECM/PCM detects a malfunction and stores a DTC.

The crankshaft position (CKP) sensor consists of a rotor and a semiconductor that detects rotor position. When the engine starts, the rotor turns and the magnetic flux in the semiconductor device changes. The changes of magnetic flux are converted into pulsing signals to the engine control module (ECM)/powertrain control module (PCM). The CKP sensor detects injection/ignition timing for each cylinder and engine speed.

If an abnormal amount of pulsing signals from the CKP sensor are detected, a malfunction is detected and a DTC is stored.

Camshaft position (CMP) sensor A detects the intake camshaft timing and sends pulsing signals to the engine control module (ECM)/powertrain control module (PCM). The ECM/PCM determines the advance or the retard of the camshaft timing according to the signals from the crankshaft position (CKP) sensor and CMP sensor A. If the pulse deviates from a set range over a specified time period while the variable valve timing control (VTC) is not activated, or the timing of the camshaft deviates from a set range over a specified time period while the engine is running with the VTC activated, a malfunction is detected and a DTC is stored.

Camshaft position (CMP) sensor A detects the intake camshaft timing and sends pulsing signals to the engine control module (ECM)/powertrain control module (PCM). The ECM/PCM determines the advance or the retard of the camshaft timing according to the signals from the crankshaft position (CKP) sensor and CMP sensor A. If the number of pulsing signals from CMP sensor A during intervals between the CKP standard pulses is more or less than the proper number, a malfunction is detected and a DTC is stored.

The camshaft position (CMP) sensor B consists of a rotor and a semiconductor that detects rotor position. When the rotor turns after starting the engine, the changes of magnetic flux in the semiconductor are converted into pulsing signals to the engine control module (ECM)/powertrain control module (PCM). The CMP sensor B detects the top dead center of each cylinder for fuel injection timing.

If CMP sensor B pulsing signals are detected an abnormal number of times due to noise, a malfunction is detected and a DTC is stored.

The three way catalytic converter (TWC) converts hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) in the exhaust gas to water vapor, carbon dioxide (CO2), and dinitrogen (N2).

The TWC efficiency does not depend entirely on engine conditions or the deterioration level of the TWC. It can be optimized by stabilizing the secondary HO2S output.

If the TWC deteriorates, the air/fuel ratio downstream of the TWC (the secondary HO2S output) often differs from the target secondary HO2S output, and the status is represented by the parameter (SIGSQRLS).

Therefore, if the SIGSQRLS exceeds a specified value for a set time, a malfunction is detected and a DTC is stored.

The evaporative emission (EVAP) leak detection system uses a vacuum-retention (decompression) method to check for vacuum leaks. This method detects leakage by monitoring the vacuum retention ability after applying vacuum to the EVAP system (from the EVAP canister purge valve to the fuel tank).

Here is an overview of the malfunction detection using this method

Step 1: Judgment as normal operation (no 0.04 inch leak/no 0.02 inch leak) < internal pressure monitor>

Step 2: Detection of 0.04 inch leak < decompressing monitor> (including the purge flow failure detection and the fuel fill cap loose/off detection)

Step 3: Detection of 0.02 inch leak < decompressing monitor> (including the purge flow failure detection and the fuel fill cap loose/off detection)

The methods used in Step 2 and Step 3 are basically the same. Here are the details

Step 1

After starting the engine, the engine control module (ECM)/powertrain control module (PCM) monitors the FTP sensor output until the EVAP purge starts, then judges it as normal (no "0.04 inch leak" nor "0.02 inch leak") by the change in the FTP sensor output.

1. If "no 0.02 inch leak" is detected, the ECM/PCM judges it as normal and the malfunction diagnosis is completed.
2. If "no 0.04 inch leak" is detected, go to the 0.02 inch leak decompressing monitor Step 3.
3. If neither "no 0.04 inch leak" nor "no 0.02 inch leak" is detected, go to Step 2.

Step 2

Detection of a 0.04 inch leak is done as follows.

The ECM/PCM decompresses the EVAP system (from the EVAP canister purge valve to the fuel tank) if all decompressing monitor conditions are met. The ECM/PCM detects a 0.04 inch leak in the EVAP system by the change in fuel tank pressure.

1. If "0.04 inch leak" is detected, the ECM/PCM judges a malfunction and completes the malfunction diagnosis.
2. If "no 0.04 inch leak" is detected, go to the 0.02 inch leak decompressing monitor Step 3.
3. If the FTP sensor output does not change enough, the ECM/PCM detects a purge flow malfunction (P0497) or a fuel fill cap loose/off malfunction (P0457) and a DTC is stored.

Step 3

Detection of a 0.02 inch leak is done as follows.

The ECM/PCM decompresses the EVAP system (from the EVAP canister purge valve to the fuel tank) if all decompressing monitor conditions are met. The ECM/PCM detects a 0.02 inch leak in the EVAP system by the change in fuel tank pressure.

1. If "0.02 inch leak" is detected, the ECM/PCM judges a malfunction and completes the malfunction diagnosis.
2. If the ECM/PCM judges "reserved", the ECM/PCM completes the malfunction diagnosis as it is.
3. If "no 0.02 inch leak" is detected, the ECM/PCM judges it as normal and completes the malfunction diagnosis.
4. If the FTP sensor output does not change enough, a purge flow malfunction (P0497) or a fuel fill cap loose/off malfunction (P0457) is detected and a DTC is stored.

The evaporative emission (EVAP) canister purge valve is attached to the vacuum port between the EVAP canister and the intake manifold. The engine control module (ECM)/powertrain control module (PCM) does not turn on the EVAP canister purge valve when the engine coolant temperature is 131°F (55°C) or less. The ECM/PCM adjusts the amount of fuel vapor sent to the engine by controlling the EVAP canister purge valve duty cycle.

When the return signal does not change according to the EVAP canister purge valve output for a set time, the ECM/PCM detects a malfunction, and a DTC is stored.

The fuel tank pressure (FTP) sensor is installed on the evaporative emission (EVAP) canister. The FTP sensor is used to detect leaks in the EVAP system. The engine control module (ECM)/powertrain control module (PCM) monitors the FTP sensor output voltage. The FTP sensor output voltage rises as the fuel tank pressure increases. Conversely, the FTP sensor output voltage drops as the fuel tank pressure decreases. Rapid changes in the FTP sensor output voltage due to electrical noise or an intermittent open during the EVAP leak detection may cause incorrect leak detection, so abnormal output is monitored.

If the FTP sensor output voltage changes a specified number of times within a set time, the ECM/PCM detects a malfunction and stores a DTC.

The fuel tank pressure (FTP) sensor is installed on the evaporative emission (EVAP) canister and detects the fuel tank pressure. The FTP sensor is used to detect leaks in the EVAP system.

The engine control module (ECM)/powertrain control module (PCM) monitors the FTP sensor output voltage. The FTP sensor output voltage rises as the fuel tank pressure increases. Conversely, the FTP sensor output voltage drops as the fuel tank pressure decreases. If the FTP sensor output voltage does not reach a target value within a set time after starting the engine in a cold condition, the ECM/PCM detects a malfunction and stores a DTC.

The fuel tank pressure (FTP) sensor is installed on the evaporative emission (EVAP) canister and detects the fuel tank pressure. The FTP sensor is used to detect leaks in the EVAP system.

The engine control module (ECM)/powertrain control module (PCM) monitors the FTP sensor output voltage. The FTP sensor output voltage rises as the fuel tank pressure increases. Conversely, the FTP sensor output voltage drops as the fuel tank pressure decreases. If the FTP sensor output voltage is higher than a target value for a set time after starting the engine in a cold condition, the ECM/PCM detects a malfunction and stores a DTC.

The evaporative emission (EVAP) leak detection system uses a vacuum-retention (decompression) method to check for vacuum leaks. This method detects leakage by monitoring the vacuum retention ability after applying vacuum to the EVAP system (from the EVAP canister purge valve to the fuel tank).

Here is an overview of the malfunction detection using this method

Step 1: Judgment as normal operation (no 0.04 inch leak/no 0.02 inch leak) < internal pressure monitor>

Step 2: Detection of 0.04 inch leak < decompressing monitor> (including the purge flow failure detection and the fuel fill cap loose/off detection)

Step 3: Detection of 0.02 inch leak < decompressing monitor> (including the purge flow failure detection and the fuel fill cap loose/off detection)

The methods used in Step 2 and Step 3 are basically the same. Here are the details

Step 1

After starting the engine, the engine control module (ECM)/powertrain control module (PCM) monitors the FTP sensor output until the EVAP purge starts, then judges it as normal (no "0.04 inch leak" nor "0.02 inch leak") by the change in the FTP sensor output.

1. If "no 0.02 inch leak" is detected, the ECM/PCM judges it as normal and the malfunction diagnosis is completed.
2. If "no 0.04 inch leak" is detected, go to the 0.02 inch leak decompressing monitor Step 3.
3. If neither "no 0.04 inch leak" nor "no 0.02 inch leak" is detected, go to Step 2.

Step 2

Detection of a 0.04 inch leak is done as follows.

The ECM/PCM decompresses the EVAP system (from the EVAP canister purge valve to the fuel tank) if all decompressing monitor conditions are met. The ECM/PCM detects a 0.04 inch leak in the EVAP system by the change in fuel tank pressure.

1. If "0.04 inch leak" is detected, the ECM/PCM judges a malfunction and completes the malfunction diagnosis.
2. If "no 0.04 inch leak" is detected, go to the 0.02 inch leak decompressing monitor Step 3.
3. If the FTP sensor output does not change enough, the ECM/PCM detects a purge flow malfunction (P0497) or a fuel fill cap loose/off malfunction (P0457) and a DTC is stored.

Step 3

Detection of a 0.02 inch leak is done as follows.

The ECM/PCM decompresses the EVAP system (from the EVAP canister purge valve to the fuel tank) if all decompressing monitor conditions are met. The ECM/PCM detects a 0.02 inch leak in the EVAP system by the change in fuel tank pressure.

1. If "0.02 inch leak" is detected, the ECM/PCM judges a malfunction and completes the malfunction diagnosis.
2. If the ECM/PCM judges "reserved", the ECM/PCM completes the malfunction diagnosis.
3. If "no 0.02 inch leak" is detected, the ECM/PCM judges it as normal and completes the malfunction diagnosis.
4. If the FTP sensor output does not change enough, a purge flow malfunction (P0497) or a fuel fill cap loose/off malfunction (P0457) is detected and a DTC is stored.

There are two conditions when the evaporative emission (EVAP) system will not hold vacuum sufficiently, and the pressure in the fuel tank doesn't become negative.

1. EVAP system low purge flow.
2. EVAP system leakage or the fuel fill cap is loose/off.

Here is a description of condition 2

The engine control module (ECM)/powertrain control module (PCM) monitors the fuel tank pressure (FTP) sensor output. If the FTP sensor output does not indicate the specified vacuum when leak checking when the fuel vapor density is high, the ECM/PCM detects a large leak (fuel fill cap loose/off) and a DTC is stored. [The malfunction detection is performed during EVAP system leak detection (P0442, P0456).]

The engine control module (ECM)/powertrain control module (PCM) adjusts the amount of fuel vapor sent to the engine by controlling the evaporative emission (EVAP) canister purge valve. If the EVAP canister purge valve is stuck open, engine vacuum flows into the purge line before purge control starts when starting the engine. The ECM/PCM monitors the fuel tank pressure (FTP) sensor output when purge control starts. If the FTP sensor output indicates negative pressure, the ECM/PCM detects a malfunction in the EVAP canister purge valve, and a DTC is stored.

There are two conditions when the evaporative emission (EVAP) system will not hold vacuum sufficiently, and the pressure in the fuel tank doesn't become negative.

1. EVAP system low purge flow.
2. EVAP system leakage or the fuel fill cap is loose/off.

Here is a description of condition 1

The malfunction detection is done during EVAP system leak detection (P0442, P0456).

The engine control module (ECM)/powertrain control module (PCM) monitors the fuel tank pressure (FTP) sensor output. If the FTP sensor output does not indicate the prescribed negative pressure when purging, the ECM/PCM detects a malfunction and a DTC is stored.

The evaporative emission (EVAP) canister vent shut valve is attached to the EVAP canister to control the venting of the EVAP canister to atmosphere.

The EVAP canister vent shut valve is open (open to atmosphere) when the VSV signal is OFF.

If the return signal is "Low" when the engine control module (ECM)/powertrain control module (PCM) outputs the "ON" signal to the EVAP canister vent shut valve, the ECM/PCM detects a malfunction and a DTC is stored.

The evaporative emission (EVAP) canister vent shut valve is attached to the EVAP canister to control the venting of the EVAP canister to atmosphere.

The EVAP canister vent shut valve is open (open to atmosphere) when the VSV signal is OFF.

If the return signal is "ON" when the engine control module (ECM)/powertrain control module (PCM) outputs the "Low" signal to the EVAP canister vent shut valve, the ECM/PCM detects a malfunction and a DTC is stored.

A target idle speed that meets the engine operating conditions (coolant temperature, A/C ON or OFF, etc.) is stored in the engine control module (ECM)/powertrain control module (PCM). The ECM/PCM monitors and controls the idle speed so that the actual idle speed is equal to the target idle speed. If the actual idle speed varies beyond a specified value from the target speed over a certain period of time, the ECM/PCM detects a malfunction in the idle speed control system and a DTC is stored.

A target idle speed that meets the engine operating conditions (coolant temperature, A/C ON or OFF, etc.) is stored in the engine control module (ECM)/powertrain control module (PCM). The ECM/PCM monitors and controls the idle speed so that the actual idle speed is equal to the target idle speed. If the actual idle speed varies beyond a specified value from the target speed over a certain period of time, the ECM/PCM detects a malfunction in the idle speed control system and a DTC is stored.

The target idle speed is in the engine control module (ECM)/powertrain control module (PCM) memory for various engine conditions (coolant temperature, A/C operation, and other functions). The ECM/PCM keeps the actual idle speed at the target idle speed by switching the idle air control (IAC) valve ON/OFF to control the intake airflow. In addition, the IAC valve functions as the fast idle valve to control the speed according to the engine coolant temperature. If the duty cycle signals are not input to a circuit that checks return signals in the ECM/PCM, a malfunction is detected and a DTC is stored.

The alternator is driven by the engine and generates electricity to supply the necessary power to the electrical system and to charge the battery. The alternator voltage target values of 14.5 V and 12.5 V are achieved by switching the alternator control mode (controlled by the engine control module (ECM)/powertrain control module (PCM)). The alternator output signal is sent to the ECM/PCM, and it varies according to the battery's state of charge, the electrical load, and engine rpm.

When the IGP (power source) terminal voltage is a set value or less and this condition continues for a set time, the ECM/PCM detects a malfunction and a DTC is stored.

If there is a short to ground in the harness between the engine control module (ECM)/powertrain control module (PCM) and the PGM-FI main relay 1, the PGM-FI main relay 1 stays ON even though the ignition switch is OFF, and the ECM/PCM remains active. However, the engine is not running because the power for the gauges, the ignition, and the fuel pump is turned OFF by the ignition switch.

When the ECM/PCM operates for a fixed time or more after the ignition switch is turned OFF, a malfunction is detected and a DTC is stored.

The multiplex communication is executed among the engine control module (ECM)/power control module (PCM), the gauge assembly unit, and the multiplex control unit (MPCS).

Each unit transmits a signal to the other units and controls the other unit's use of the necessary information.

When the communication from another unit cannot be received for a certain period of time or when an abnormality of the received data occurred a certain number of times, each unit detects a communication abnormality and a DTC is stored.

The engine control module (ECM)/powertrain control module (PCM) is equipped with an update program to update its control program. The programs in the CPU of the ECM/PCM are classified as a ECM/PCM program (update-capable program) and a program for the update function (non-updateable program). The program update only updates the powertrain control program.

When the ECM/PCM power is turned off during an update, the power for the update function is lost, and the update process stops. When the program update is stopped before it is completed, the ECM/PCM stores a DTC that indicates the update is not finished.

The engine control module (ECM)/powertrain control module (PCM) is equipped with a keep-alive memory. The data (control learn data etc) for powertrain control and information (Vehicle Identify Number (VIN) etc) related to the vehicle control is stored in the keep alive memory, so that it can be maintained even when power is not supplied to the ECM/PCM such as when the battery is disconnected. When power is restored to the ECM/PCM, the CPU retrieves the stored information from the keep-alive memory, but when the data retrieval process is not finished normally, a malfunction is detected and a DTC is stored.

The CPU writes data to the keep-alive memory from the CPU: Control related data is written when the ignition is turned on, and vehicle information when commanded from the HDS.

If the data writing process is not completed normally, a malfunction is detected and a DTC is stored.

If something is wrong in the engine control module (ECM)/powertrain control module (PCM), and the monitor signal from the digital knock system (DKS) CPU is not received for a set period of time, or a signal communication error remains for a set period time, the ECM/PCM detects a malfunction and a DTC is stored.

The Engine control module (ECM)/powertrain control module (PCM) stores a vehicle identification number (VIN) in the keep-alive memory and outputs the VIN according to the command from the scan tool.

The VIN for each vehicle is registered to the ECM/PCM using the scan tool. The registered VIN is read by the CPU from the keep-alive memory after the ignition is turned on or after the Clear command is executed.

If the VIN is not registered in the keep-alive memory when the ignition is turned on or when the Clear command is executed, it is detected as a VIN unregistered condition and a DTC is stored.

After the ignition switch is turned off, the engine control module (ECM)/powertrain control module (PCM) does not shut down immediately. After finishing a predetermined process according to the request of each device and system, the power supply is automatically disconnected (self shut-down function). The ECM/PCM power is disconnected by controlling PGM-FI main relay 1 (FI MAIN).

During a normal ECM/PCM shut down, the shut down process is executed by the CPU, PGM-FI main relay 1 (FI MAIN) is turned off, and the voltage to the ECM/PCM is turned off to shut down the ECM/PCM. When the voltage to the ECM/PCM is turned off and the ECM/PCM shuts down without the normal shut down procedure, a malfunction in the PGM-FI main relay 1 (FI MAIN) control circuit is detected and a DTC is stored.

The transmission range switch is attached to the control shaft. Operation of the shift lever makes the control shaft rotate via the shift cable. The A/T gear position indicator indicates which position is selected according to the signal Low/High combinations which vary based on shift lever position. The control shaft changes the position of the transmission range switch, activates the manual valve, and switches hydraulic pressure to shift the transmission through forward/neutral/reverse. The transmission range switch signal is used to determine the shift schedule. The voltage is 12 V (High) at the powertrain control module (PCM) input terminal when each transmission range switch position is open, and it is 0 V (Low) when each switch is closed. If the PCM detects multiple switch inputs instead of the correct switch input for the selected range at that time, it detects a malfunction and stores a DTC.

The transmission range switch is attached to the control shaft. Operation of the shift lever makes the control shaft rotate via the shift cable. The A/T gear position indicator indicates which position is selected according to the signal Low/High combinations which vary based on the control shaft rotational angle. The control shaft changes the position of the transmission range switch, activates the manual valve, and switches hydraulic pressure to shift the transmission through forward/neutral/reverse. The transmission range switch signal is used to determine the shift schedule. The voltage is 12 V (High) at the powertrain control module (PCM) input terminal when each transmission range switch position is open, and it is 0 V (Low) when each switch is closed. If the FWD switch stays open while the vehicle repeatedly accelerates to a specified vehicle speed and then stops despite being in the D position, the PCM detects a malfunction in the transmission range switch (open) and stores a DTC.

The ATF temperature sensor is a thermistor type sensor whose resistance changes according to the change in ATF temperature. The powertrain control module (PCM) sends a 5 V reference voltage to the grounded sensor through a pull-up resistor. When the ATF temperature is low, the sensor resistance increases and the PCM detects a high signal voltage. As the ATF temperature rises, the sensor resistance decreases and the PCM detects a low signal voltage.

If the ATF temperature sensor signal does not change, the PCM detects a malfunction and a DTC is stored.

The ATF temperature sensor is a thermistor type sensor whose resistance changes according to the change in ATF temperature. The powertrain control module (PCM) sends a 5 V reference voltage to the grounded sensor through a pull-up resistor. When the ATF temperature is low, the sensor resistance increases and the PCM detects a high signal voltage. As the ATF temperature rises, the sensor resistance decreases and the PCM detects a low signal voltage.

When the ATF temperature sensor signal voltage to the PCM is under the specification, indicating that the temperature is above the specification (a short to ground), a malfunction is detected and a DTC is stored.

The ATF temperature sensor is a thermistor type sensor whose resistance changes according to the change in ATF temperature. The powertrain control module (PCM) sends a 5 V reference voltage to the grounded sensor through a pull-up resistor. When the ATF temperature is low, the sensor resistance increases and the PCM detects a high signal voltage. As the ATF temperature rises, the sensor resistance decreases and the PCM detects a low signal voltage.

When the ATF temperature sensor signal voltage to the PCM is above the specification, indicating that the temperature is under the specification (open), a malfunction is detected and a DTC is stored.

The input shaft (mainshaft) speed sensor is attached to the outside of the transmission housing. The input shaft (mainshaft) speed sensor generates a pulsing signal according to the speed of the mainshaft idler gear on the mainshaft. Using that signal, the powertrain control module (PCM) determines the speed of the mainshaft. If no pulses occur with the mainshaft rotating, the PCM detects a malfunction that may be caused by an open, a temporary open, or a short to ground. Based on the velocity ratio measured by the output shaft (countershaft) speed sensor and the input shaft (mainshaft) speed sensor, a malfunction is detected and a DTC is stored.

The input shaft (mainshaft) speed sensor is attached to the outside of the transmission housing. The input shaft (mainshaft) speed sensor generates a pulsing signal according to the speed of the mainshaft idler gear on the mainshaft. Using that signal, the powertrain control module (PCM) determines the speed of the mainshaft. If no pulses occur with the mainshaft rotating, the PCM detects a malfunction that may be caused by an open, a temporary open, or a short to ground. Based on the correlation between the vehicle speed measured by the output shaft (countershaft) speed sensor and the input shaft (mainshaft) speed sensor, a malfunction is detected and a DTC is stored.

The input shaft (mainshaft) speed sensor is attached to the outside of the transmission housing. The input shaft (mainshaft) speed sensor generates a pulsing signal according to the speed of the mainshaft idler gear on the mainshaft. Using that signal, the powertrain control module (PCM) determines the speed of the mainshaft. If no pulses occur with the mainshaft rotating, the PCM detects a malfunction that may be caused by an open, a temporary open, or a short to ground. Based on the fluctuation of the vehicle speed measured by the input shaft (mainshaft) speed sensor, a malfunction is detected and a DTC is stored.

The output shaft (countershaft) speed sensor is attached to the outside of the transmission housing. The output shaft (countershaft) speed sensor generates a pulsing signal according to the speed of the park gear on the countershaft. Using that signal, the powertrain control module (PCM) determines the speed of the countershaft. If pulse dropouts occur with the countershaft rotating, the PCM detects a malfunction that may be caused by an open, a temporary open, or a short to ground. Based on the velocity ratio measured by the input shaft (mainshaft) speed sensor and the output shaft (countershaft) speed sensor, a malfunction is detected and a DTC is stored.

The output shaft (countershaft) speed sensor is attached to the outside of the transmission housing. The output shaft (countershaft) speed sensor generates a pulsing signal according to the speed of the park gear on the countershaft. Using that signal, the powertrain control module (PCM) determines the speed of the countershaft. If pulse dropouts occur with the countershaft rotating, the PCM detects a malfunction that may be caused by an open, a temporary open, or a short to ground. Based on the correlation between the vehicle speed measured by the output shaft (countershaft) speed sensor and the input shaft (mainshaft) speed sensor, a malfunction is detected and a DTC is stored.

The output shaft (countershaft) speed sensor is attached to the outside of the transmission housing. The output shaft (countershaft) speed sensor generates a pulsing signal according to the speed of the park gear on the countershaft. Using that signal, the powertrain control module (PCM) determines the speed of the countershaft. If pulse dropouts occur with the countershaft rotating, the PCM detects a malfunction that may be caused by an open, a temporary open, or a short to ground. Based on the fluctuation of the vehicle speed measured by the output shaft (countershaft) speed sensor, a malfunction is detected and a DTC is stored.

To engage 1st gear, line pressure is supplied to the 1st clutch piston, the 1st clutch is engaged, and the secondary shaft and the secondary shaft 1st gear are connected and revolve together. Hydraulic pressure is supplied to the 1st clutch through the ATF strainer --> the ATF pump --> the regulator valve --> the manual valve --> the shift valves --> the feed pipe --> 1st clutch piston. (The shift valve failure in the supplying route above is detected by the malfunction detection of each shift solenoid valve.) The powertrain control module (PCM) computes the ratio of the mainshaft speed to the countershaft speed. When the ratio is not the 1st gear ratio, it is detected as a malfunction of the hydraulic circuit or the 1st clutch, and a DTC is stored.

To engage 2nd gear, line pressure is supplied to the 2nd clutch piston, the 2nd clutch is engaged, and the secondary shaft and the secondary shaft 2nd gear are connected and revolve together. Hydraulic pressure is supplied to the 2nd clutch through the ATF strainer --> the ATF pump --> the regulator valve --> the manual valve --> the shift valves --> the feed pipe --> 2nd clutch piston. (The shift valve failure in the supplying route above is detected by the malfunction detection of each shift solenoid valve.) The powertrain control module (PCM) computes the ratio of the mainshaft speed to the countershaft speed. When the ratio is not the 2nd gear ratio, it is detected as a malfunction of the hydraulic circuit or the 2nd clutch, and a DTC is stored.

To engage 3rd gear, line pressure is supplied to the 3rd clutch piston, the 3rd clutch is engaged, and the mainshaft and the mainshaft 3rd gear are connected and revolve together. Hydraulic pressure is supplied to the 3rd clutch through the ATF strainer --> the ATF pump --> the regulator valve --> the manual valve --> the shift valves --> the feed pipe --> 3rd clutch piston. (The shift valve failure in the supplying route above is detected by the malfunction detection of each shift solenoid valve.) The powertrain control module (PCM) computes the ratio of the mainshaft speed to the countershaft speed. When the ratio is not the 3rd gear ratio, it is detected as a malfunction of the hydraulic circuit or the 3rd clutch, and a DTC is stored.

To engage 4th gear, line pressure is supplied to the 4th clutch piston, the 4th clutch is engaged, and the mainshaft and the mainshaft 4th gear are connected and revolve together. Hydraulic pressure is supplied to the 4th clutch through the ATF strainer --> the ATF pump --> the regulator valve --> the manual valve --> the shift valves --> the feed pipe --> 4th clutch piston. (The shift valve failure in the supplying route above is detected by the malfunction detection of each shift solenoid valve.) The powertrain control module (PCM) computes the ratio of the mainshaft speed to the countershaft speed. When the ratio is not the 4th gear ratio, it is detected as a malfunction of the hydraulic circuit or the 4th clutch, and a DTC is stored.

The power transfer capacity of the torque converter clutch is controlled by the balance of automatic transmission fluid (ATF) supplied to and discharged from the torque converter. When hydraulic pressure is applied internally, the torque converter clutch turns ON, and when hydraulic pressure is applied from the back pressure side, the lock-up clutch turns OFF. As the hydraulic pressure from the internal pressure side increases, the power transfer capacity of the torque converter clutch increases. The direction of hydraulic pressure supply is switched by shift solenoid valve E and the lock-up shift valve. ATF is supplied from the internal pressure side to shift solenoid valve E when the signal from the powertrain control module (PCM) is ON (12 V), and ATF is supplied from the back pressure side when it is OFF (0 V). The balance of internal pressure and back pressure is controlled by A/T clutch pressure control solenoid valve A and the lock-up control valve. A/T clutch pressure control solenoid valve A maximizes the power transfer capacity of the torque converter clutch when the signal from the PCM is ON (1 A), and it minimizes the power transfer capacity of the torque converter clutch when the signal from the PCM is OFF (0 A). If the ratio of engine speed and mainshaft speed is not about 1:1 while the PCM is issuing the command to turn shift solenoid valve E and A/T clutch pressure control solenoid valve A ON, the PCM detects a faulty lock-up control system and stores a DTC.

Hydraulic pressure to each clutch is controlled by the shift valve. The shift valve activates according to the ON/OFF status of shift solenoid valves A, B, C, and E. Hydraulic pressure supply in D position is shown above. The line pressure or the clutch pressure control pressure (CPC A, CPC B, or CPC C) is supplied to each clutch by the shift valve activated. The powertrain control module (PCM) computes the actual ratio of mainshaft and countershaft revolutions. If a difference between the actual ratio and the commanded gear occurs when shifting to each gear position, a malfunction in A/T clutch pressure control solenoid valve A or the hydraulic system is detected and a DTC is stored.

Shift solenoid valve A is installed in the transmission housing. It is controlled by the ON/OFF signal from the powertrain control module (PCM), to apply line pressure to shift valve A. The signal from the PCM is output to apply clutch pressure control pressure to the proper gear change clutch according to the gear change schedule. When the signal to shift solenoid valve A from the PCM is OFF, line pressure is discharged, and shift valve A is inactive. When the signal to shift solenoid valve A from the PCM is ON, line pressure is applied to shift valve A, and it operates against the shift valve A spring. The PCM monitors the mainshaft speed and the countershaft speed at the gear change determined by the shift schedule. When an improper gear ratio is output compared to the predetermined gear change mode, a shift solenoid valve A ON failure is detected and a DTC is stored.

Shift solenoid valve C is installed in the transmission housing. It is controlled by the ON/OFF signal from the powertrain control module (PCM), to apply line pressure to shift valve C. The signal from the PCM is output to apply clutch pressure control pressure to the proper gear change clutch according to the gear change schedule. When the signal to shift solenoid valve C from the PCM is OFF, line pressure is discharged, and shift valve C is inactive. When the signal to shift solenoid valve C from the PCM is ON, line pressure is applied to shift valve C, and it operates against the shift valve C spring. The PCM monitors the mainshaft speed and the countershaft speed at the gear change determined by the shift schedule. When an improper gear ratio is output compared to the predetermined gear change mode, a shift solenoid valve C OFF failure is detected and a DTC is stored.

Shift solenoid valve E is installed in the transmission housing. It is controlled by the ON/OFF signal from the powertrain control module (PCM), to apply line pressure to shift valve E. The signal from the PCM is output to apply clutch pressure control pressure to the proper gear change clutch according to the gear change schedule. When the signal to shift solenoid valve E from the PCM is OFF, line pressure is discharged, and shift valve E is inactive. When the signal to shift solenoid valve E from the PCM is ON, line pressure is applied to shift valve E, and it operates against the shift valve E spring. The PCM monitors the mainshaft speed and the countershaft speed at the gear change determined by the shift schedule. When an improper gear ratio is output compared to the predetermined gear change mode, a shift solenoid valve E OFF failure is detected and a DTC is stored.

Hydraulic pressure to each clutch is controlled by the shift valve. The shift valve activates according to the ON/OFF status of shift solenoid valves A, B, C, and E. Hydraulic pressure supply in D position is shown above. The line pressure or the clutch pressure control pressure (CPC A, CPC B, or CPC C) is supplied to each clutch by the shift valve activated. The powertrain control module (PCM) computes the actual ratio of mainshaft and countershaft revolutions. If a difference between the actual ratio and the commanded gear occurs when shifting to each gear position, a malfunction in A/T clutch pressure control solenoid valve B or the hydraulic system is detected and a DTC is stored.

Hydraulic pressure to each clutch is controlled by the shift valve. The shift valve activates according to the ON/OFF status of shift solenoid valves A, B, C, and E. Hydraulic pressure supply in D position is shown above. The line pressure or the clutch pressure control pressure (CPC A, CPC B, or CPC C) is supplied to each clutch by the shift valve activated. The powertrain control module (PCM) computes the actual ratio of mainshaft and countershaft revolutions. If a difference between the actual ratio and the commanded gear occurs when shifting to each gear position, a malfunction in A/T clutch pressure control solenoid valve B or the hydraulic system is detected and a DTC is stored.

This fault code is a general (specified by SAE) DTC that is stored at a time the following DTC codes (P1731, P01732, P1735 and P1736) are detected.

Hydraulic pressure to each clutch is controlled by the shift valve. The shift valve activates according to the ON/OFF status of shift solenoid valves A, B, C, and E. Hydraulic pressure supply in D position is shown above. The line pressure or the clutch pressure control pressure (CPC A, CPC B, or CPC C) is supplied to each clutch by the shift valve activated. The powertrain control module (PCM) computes the actual ratio of mainshaft and countershaft revolutions. If a difference between the actual ratio and the commanded gear occurs when shifting to each gear position, a malfunction in A/T clutch pressure control solenoid valve C or the hydraulic system is detected and a DTC is stored.

Hydraulic pressure to each clutch is controlled by the shift valve. The shift valve activates according to the ON/OFF status of shift solenoid valves A, B, C, and E. Hydraulic pressure supply in D position is shown above. The line pressure or the clutch pressure control pressure (CPC A, CPC B, or CPC C) is supplied to each clutch by the shift valve activated. The powertrain control module (PCM) computes the actual ratio of mainshaft and countershaft revolutions. If a difference between the actual ratio and the commanded gear occurs when shifting to each gear position, a malfunction in A/T clutch pressure control solenoid valve C or the hydraulic system is detected and a DTC is stored.

The transmission range switch is attached to the control shaft. Operation of the shift lever makes the control shaft rotate via the shift cable. The A/T gear position indicator indicates which position is selected according to the signal Low/High combinations which vary based on shift lever position. The control shaft changes the position of the transmission range switch, activates the manual valve, and switches hydraulic pressure to shift the transmission through forward/neutral/reverse. The transmission range switch signal is used to determine the shift schedule. The voltage is 12 V (High) at the powertrain control module (PCM) input terminal when each transmission range switch position is open, and it is 0 V (Low) when each switch is closed. If the RVS switch is OPEN with the shift lever in R position while shifting between the P, R, and N positions, the PCM detects a switch OPEN failure and a DTC is stored.

The 2nd clutch transmission fluid pressure switch is installed in the hydraulic pressure circuit to the 2nd clutch. When hydraulic pressure is supplied to the 2nd clutch, the switch is turned ON. When hydraulic pressure is not supplied to the 2nd clutch, the switch is turned OFF. The signal from the 2nd clutch transmission fluid pressure switch is input to the powertrain control module (PCM). The PCM detects the hydraulic pressure supply conditions at the gear change to 2nd gear (1st 2nd, 3rd 2nd) to reduce the shock that occurs at the gear change.

If the 2nd clutch transmission fluid pressure switch is ON while driving the vehicle with the speed ratio of the countershaft to mainshaft other than 2nd (the ratio is Neutral or 4th), the PCM detects a 2nd clutch transmission fluid pressure switch failure and a DTC is stored.

The 2nd clutch transmission fluid pressure switch is installed in the hydraulic pressure circuit to the 2nd clutch. When hydraulic pressure is supplied to the 2nd clutch, the switch is turned ON. When hydraulic pressure is not supplied to the 2nd clutch, the switch is turned OFF. The signal from the 2nd clutch transmission fluid pressure switch is input to the powertrain control module (PCM). The PCM detects the hydraulic pressure supply conditions at the gear change to 2nd gear (1st --> 2nd, 3rd --> 2nd) to reduce the shock that occurs at the gear change. If the 2nd clutch transmission fluid pressure switch is OFF while driving with the rotation speed ratio of the input/output pulses in 2nd gear, the PCM detects a malfunction in the 2nd clutch transmission fluid pressure switch and stores a DTC.

The 3rd clutch transmission fluid pressure switch is installed in the hydraulic pressure circuit to the 3rd clutch. When hydraulic pressure is supplied to the 3rd clutch, the switch is turned ON. When hydraulic pressure is not supplied to the 3rd clutch, the switch is turned OFF. The signal from the 3rd clutch transmission fluid pressure switch is input to the powertrain control module (PCM). The PCM detects the hydraulic pressure supply conditions at the gear change to 3rd gear (2nd 3rd, 4th 3rd) to reduce the shock that occurs at the gear change.

If the 3rd clutch transmission fluid pressure switch is ON while driving the vehicle with the speed ratio of the countershaft to mainshaft in other than 3rd gear (the ratio is Neutral or 4th), the PCM detects a 3rd clutch transmission fluid pressure switch failure and a DTC is stored.

The 3rd clutch transmission fluid pressure switch is installed in the hydraulic pressure circuit to the 3rd clutch. When hydraulic pressure is supplied to the 3rd clutch, the switch is turned ON. When hydraulic pressure is not supplied to the 3rd clutch, the switch is turned OFF. The signal from the 3rd clutch transmission fluid pressure switch is input to the powertrain control module (PCM). The PCM detects the hydraulic pressure supply conditions at the gear change to 3rd gear (2nd 3rd, 4th 3rd) to reduce the shock that occurs at the gear change. If the 3rd clutch transmission fluid pressure switch is OFF while driving with the rotation speed ratio of the input/output pulses in 3rd gear, the PCM detects a malfunction in the 3rd clutch transmission fluid pressure switch and stores a DTC.

A/T clutch pressure control solenoid valve A is used for clutch pressure control and lock-up control. A spool in A/T clutch pressure control solenoid valve A pushes a valve according to the duty cycle that is controlled by the powertrain control module (PCM) to pressurize fluid so the hydraulic pressure is proportional to the current. The PCM measures the current flowing through A/T clutch pressure control solenoid valve A and uses feedback control to compensate the difference between the actual current and the commanded one. If the measured current for the PCM output duty cycle is not within a specified range (open or short), a malfunction is detected and a DTC is stored.

A/T clutch pressure control solenoid valve A is used for clutch pressure control and lock-up control. A spool in A/T clutch pressure control solenoid valve A pushes a valve according to the duty cycle that is controlled by the powertrain control module (PCM) to pressurize fluid so the hydraulic pressure is proportional to the current. The PCM measures the current flowing through A/T clutch pressure control solenoid valve A and uses feedback control to compensate the difference between the actual current and the commanded one. If the measured current for the PCM output duty cycle is not within a specified range (open or short), a malfunction is detected and a DTC is stored.

A/T clutch pressure control solenoid valve B is used for clutch pressure control. A spool in A/T clutch pressure control solenoid valve B pushes a valve according to the duty cycle that is controlled by the powertrain control module (PCM) to pressurize fluid so the hydraulic pressure is proportional to the current. The PCM measures the current flowing through A/T clutch pressure control solenoid valve B and uses feedback control to compensate the difference between the actual current and the commanded one. If the measured current for the PCM output duty cycle is not within a specified range (open or short), a malfunction is detected and a DTC is stored.

A/T clutch pressure control solenoid valve B is used for clutch pressure control. A spool in A/T clutch pressure control solenoid valve B pushes a valve according to the duty cycle that is controlled by the powertrain control module (PCM) to pressurize fluid so the hydraulic pressure is proportional to the current. The PCM measures the current flowing through A/T clutch pressure control solenoid valve B and uses feedback control to compensate the difference between the actual current and the commanded one. If the measured current for the PCM output duty cycle is not within a specified range (open or short), a malfunction is detected and a DTC is stored.

A/T clutch pressure control solenoid valve C is used for clutch pressure control. A spool in A/T clutch pressure control solenoid valve C pushes a valve according to the duty cycle that is controlled by the powertrain control module (PCM) to pressurize fluid so the hydraulic pressure is proportional to the current. The PCM measures the current flowing through A/T clutch pressure control solenoid valve C and uses feedback control to compensate the difference between the actual current and the commanded one. If the measured current for the PCM output duty cycle is not within a specified range (open or short), a malfunction is detected and a DTC is stored.

A/T clutch pressure control solenoid valve C is used for clutch pressure control. A spool in A/T clutch pressure control solenoid valve C pushes a valve according to the duty cycle that is controlled by the powertrain control module (PCM) to pressurize fluid so the hydraulic pressure is proportional to the current. The PCM measures the current flowing through A/T clutch pressure control solenoid valve C and uses feedback control to compensate the difference between the actual current and the commanded one. If the measured current for the PCM output duty cycle is not within a specified range (open or short), a malfunction is detected and a DTC is stored.

When shift solenoid valves A, B, C, and E are turned ON, the hydraulic pressure circuit opens. The hydraulic pressure circuit supplies/discharges hydraulic pressure to/from each clutch according to the combination of the ON/OFF status of those valves and the shift valves. The powertrain control module (PCM) commands the driver circuit to turn on the shift solenoid valve. The circuit diagnoses malfunctions such as a circuit short or open, and sends back a return signal during the PCM's command. When the return signal does not match the PCM command, a malfunction is detected by the PCM. The malfunction is detected when the return signal does not match the PCM command to turn ON the shift solenoid valve, and a DTC is stored.

When shift solenoid valves A, B, C, and E are turned ON, the hydraulic pressure circuit opens. The hydraulic pressure circuit supplies/discharges hydraulic pressure to/from each clutch according to the combination of the ON/OFF status of those valves and the shift valves. The powertrain control module (PCM) commands the driver circuit to turn on the shift solenoid valve. The circuit diagnoses malfunctions such as a circuit short or open, and sends back a return signal during the PCM's command. When the return signal does not match the PCM command, a malfunction is detected by the PCM. The malfunction is detected when the return signal does not match the PCM command to turn OFF the shift solenoid valve, and a DTC is stored.

When shift solenoid valves A, B, C, and E are turned ON, the hydraulic pressure circuit opens. The hydraulic pressure circuit supplies/discharges hydraulic pressure to/from each clutch according to the combination of the ON/OFF status of those valves and the shift valves. The powertrain control module (PCM) commands the driver circuit to turn on the shift solenoid valve. The circuit diagnoses malfunctions such as a circuit short or open, and sends back a return signal during the PCM's command. When the return signal does not match the PCM command, a malfunction is detected by the PCM. The malfunction is detected when the return signal does not match the PCM command to turn ON the shift solenoid valve, and a DTC is stored.

When shift solenoid valves A, B, C, and E are turned ON, the hydraulic pressure circuit opens. The hydraulic pressure circuit supplies/discharges hydraulic pressure to/from each clutch according to the combination of the ON/OFF status of those valves and the shift valves. The powertrain control module (PCM) commands the driver circuit to turn on the shift solenoid valve. The circuit diagnoses malfunctions such as a circuit short or open, and sends back a return signal during the PCM's command. When the return signal does not match the PCM command, a malfunction is detected by the PCM. The malfunction is detected when the return signal does not match the PCM command to turn OFF the shift solenoid valve, and a DTC is stored.

When shift solenoid valves A, B, C, and E are turned ON, the hydraulic pressure circuit opens. The hydraulic pressure circuit supplies/discharges hydraulic pressure to/from each clutch according to the combination of the ON/OFF status of those valves and the shift valves. The powertrain control module (PCM) commands the driver circuit to turn on the shift solenoid valve. The circuit diagnoses malfunctions such as a circuit short or open, and sends back a return signal during the PCM's command. When the return signal does not match the PCM command, a malfunction is detected by the PCM. The malfunction is detected when the return signal does not match the PCM command to turn ON the shift solenoid valve, and a DTC is stored.

When shift solenoid valves A, B, C, and E are turned ON, the hydraulic pressure circuit opens. The hydraulic pressure circuit supplies/discharges hydraulic pressure to/from each clutch according to the combination of the ON/OFF status of those valves and the shift valves. The powertrain control module (PCM) commands the driver circuit to turn on the shift solenoid valve. The circuit diagnoses malfunctions such as a circuit short or open, and sends back a return signal during the PCM's command. When the return signal does not match the PCM command, a malfunction is detected by the PCM. The malfunction is detected when the return signal does not match the PCM command to turn OFF the shift solenoid valve, and a DTC is stored.

When shift solenoid valves A, B, C, and E are turned ON, the hydraulic pressure circuit opens. The hydraulic pressure circuit supplies/discharges hydraulic pressure to/from each clutch according to the combination of the ON/OFF status of those valves and the shift valves. The powertrain control module (PCM) commands the driver circuit to turn on the shift solenoid valve. The circuit diagnoses malfunctions such as a circuit short or open, and sends back a return signal during the PCM's command. When the return signal does not match the PCM command, a malfunction is detected by the PCM. The malfunction is detected when the return signal does not match the PCM command to turn ON the shift solenoid valve, and a DTC is stored.

When shift solenoid valves A, B, C, and E are turned ON, the hydraulic pressure circuit opens. The hydraulic pressure circuit supplies/discharges hydraulic pressure to/from each clutch according to the combination of the ON/OFF status of those valves and the shift valves. The powertrain control module (PCM) commands the driver circuit to turn on the shift solenoid valve. The circuit diagnoses malfunctions such as a circuit short or open, and sends back a return signal during the PCM's command. When the return signal does not match the PCM command, a malfunction is detected by the PCM. The malfunction is detected when the return signal does not match the PCM command to turn OFF the shift solenoid valve, and a DTC is stored.

The variable valve timing control (VTC) system controls the phase of the intake camshaft. It uses oil pressure to operate the VTC actuator so the valve timing is optimized depending on driving conditions. The engine control module (ECM)/powertrain control module (PCM) monitors the phase control command and the actual timing of the camshaft by using camshaft position (CMP) sensor A. If an over-advanced camshaft phase (compared to the directed value) continues or when the camshaft phase is otherwise abnormal, a malfunction is detected and a DTC is stored.

The barometric pressure (BARO) sensor is built into the engine control module (ECM)/powertrain control module (PCM), and it monitors atmospheric pressure. The ECM/PCM estimates appropriate intake airflow from the manifold absolute pressure (MAP) sensor output voltage and BARO sensor output voltage. When BARO sensor output voltage is within the specified range, a malfunction is detected and a DTC is stored.

Two engine coolant temperature sensors and one intake air temperature sensor are used by the engine control module (ECM)/powertrain control module (PCM).

When the engine is stopped and enough time has passed, the temperature of the engine will equal the ambient temperature. When an inappropriate temperature is detected after comparing the temperature readings of each sensor, a malfunction in the corresponding sensor is detected and a DTC is stored.

The throttle position (TP) sensor detects the position of the throttle valve. When the throttle valve is open (low-vacuum), the manifold absolute pressure (MAP) sensor outputs a high MAP value, and when the throttle valve is closed (high-vacuum), it outputs a low MAP value.

If the TP sensor detects a throttle position that is less than the set value when the MAP sensor outputs a higher MAP value (higher pressure) than the set value, a malfunction is detected and a DTC is stored.

The throttle position (TP) sensor detects the position of the throttle valve. When the throttle valve is open (low-vacuum), the manifold absolute pressure (MAP) sensor outputs a high MAP value, and when the throttle valve is closed (high-vacuum), it outputs a low MAP value.

If the TP sensor detects a throttle position that is more than the set value when the MAP sensor outputs a lower MAP value (lower pressure) than the set value, a malfunction is detected and a DTC is stored.

The manifold absolute pressure (MAP) sensor senses manifold absolute pressure (vacuum) and converts it into electrical signals. The MAP sensor outputs low signal voltage at high-vacuum (idling) and high signal voltage at low-vacuum (throttle valve wide open).

The engine control module (ECM)/powertrain control module (PCM) compares a predetermined MAP value at a given throttle position and manifold absolute pressure to the output voltage value of the MAP sensor.

If the MAP sensor outputs lower voltage than expected, the ECM/PCM detects a malfunction and stores a DTC.

The manifold absolute pressure (MAP) sensor senses manifold absolute pressure (vacuum) and converts it into electrical signals. The MAP sensor outputs low signal voltage at high-vacuum (throttle valve closed) and high signal voltage at low-vacuum (throttle valve wide open).

The engine control module (ECM)/powertrain control module (PCM) compares a predetermined MAP value at a given throttle position and manifold absolute pressure to the output voltage value of the MAP sensor.

If the MAP sensor outputs high voltage during fuel cut-off operation for deceleration with the throttle valve fully closed, which should make the manifold absolute pressure lower, the ECM/PCM detects a malfunction and stores a DTC.

The air/fuel ratio (A/F) sensor (sensor 1) is installed in the exhaust system and detects oxygen content in the exhaust gas. The A/F sensor outputs voltage to the engine control module (ECM)/powertrain control module (PCM). A heater for the sensor element is embedded in the A/F sensor (sensor 1). When activated, it heats the sensor to stabilize and speed up the detection of oxygen content by controlling current flow through the heater. The current diminishes as the voltage applied to the element reaches a certain range because the amount of oxygen that passes through the diffusion layer is limited. The current is proportional to the oxygen content in the exhaust gas, so the air/fuel ratio is detected by the measurement of the current. The ECM/PCM compares the set target air/fuel ratio to the detected air/fuel ratio and adjusts the fuel injection duration.

If the A/F sensor (sensor 1) voltage is low, the air/fuel ratio is lean, and the ECM/PCM uses A/F feedback control to issue a Rich command. If the A/F sensor (sensor 1) voltage is high, the air/fuel ratio is rich, and the ECM/PCM uses A/F feedback control to issue a Lean command.

If the element is not activated for a set time when power is drawn by the A/F sensor (sensor 1) heater, a malfunction is detected and a DTC is stored.

If a malfunction causes the air/fuel sensor reading value to the engine control module (ECM)/powertrain control module (PCM) to deviate from the normal control area, the air/fuel ratio (A/F) sensor becomes active after the engine starts, but the air/fuel feedback does not start normally and the emissions deteriorate. When the A/F sensor output is out of the normal area, and this condition continues after the A/F sensor is active, the ECM/PCM detects a malfunction and a DTC is stored.

The electrical load detector (ELD) is built into the under-hood fuse/relay box. It monitors the current fed to the ignition switch and sends a signal to the engine control module (ECM)/powertrain control module (PCM). If the ELD output voltage is extremely low, a malfunction is detected and a DTC is stored.

The electrical load detector (ELD) is built into the under-hood fuse/relay box. It monitors the current fed to the ignition switch and sends a signal to the engine control module (ECM)/powertrain control module (PCM). If the ELD output voltage is extremely high, a malfunction is detected and a DTC is stored.

The fuel tank pressure is about 0 kPa (0 in.Hg, 0 mmHg) when starting a cold engine. When the fuel tank pressure (FTP) sensor output value is out of a specified range and the engine control module (ECM)/powertrain control module (PCM) judges that there's no other cause [no evaporative emission (EVAP) canister vent shut valve failure, etc.] of the FTP sensor zero point shift, the ECM/PCM detects an FTP sensor malfunction.

However, if the FTP sensor output when starting the engine is a prescribed negative value or less (excessive negative pressure is detected), the malfunction judgment should be done as follows because it is difficult to distinguish the FTP sensor zero point shift (P1454) from the EVAP canister vent shut valve failure (P2422).

1. If either Temporary DTC P1454 or P2422 is not stored, the ECM/PCM stores both DTCs.
2. If both P1454 and P2422 Temporary DTCs are stored and an excessive negative pressure is detected, both P1454 and P2422 DTCs are stored.
3. If either Temporary DTC P1454 or P2422 is stored and an excessive negative pressure is detected, the ECM/PCM stores the DTC of the temporary DTC that was stored.

The alternator is driven by the engine generates electricity to supply the necessary power to the electrical system and to charge the battery. The alternator voltage target values of 14.5 V and 12.5 V are achieved by switching the alternator control mode (controlled by the engine control module (ECM)/powertrain control module (PCM)). The alternator output signal is sent to the ECM/PCM, and it varies according to the battery's state of charge, the electrical load, and the engine rpm.

When the IGP terminal voltage of the ECM/PCM is a set value or more and this condition continues for a set time, a malfunction is detected and a DTC is stored.

The alternator is driven by the engine and generates electricity to supply the necessary power to the electrical system and to charge the battery. The alternator voltage target values of 14.5 V and 12.5 V are achieved by switching the alternator control mode (controlled by the engine control module (ECM)/powertrain control module (PCM)). The alternator output signal is sent to the ECM/PCM, and it varies according to the battery's state of charge, the electrical load, and the engine rpm.

When the engine speed is a specified value and the IGP terminal voltage is below a set value when the alternator is in the 14.5 V mode, and the alternator power generation amount is within the set range, and this condition continues more than a set time, the ECM/PCM detects a malfunction and a DTC is stored.

The alternator is driven by the engine and generates electricity to supply the necessary power to the electrical load and to charge the battery. The alternator voltage target values of 14.5 V and 12.5 V are achieved by switching the alternator control mode (controlled by the engine control module (ECM)/powertrain control module (PCM)). The alternator output signal is sent to the ECM/PCM, and it varies according to the battery's state of charge, the electrical load, and the engine rpm.

When the engine speed is a specified value and the IGP terminal voltage is below a set value when the alternator is in the 14.5 V mode, and the alternator power generation amount is a set range or less, and this condition continues more than a set time, the ECM/PCM detects a malfunction and a DTC is stored.

Hydraulic pressure to each clutch is controlled by the shift valve. The shift valve activates according to the ON/OFF status of shift solenoid valves A, B, C, and E. Hydraulic pressure supply in D position is shown above. The line pressure or the clutch pressure control pressure (CPC A, CPC B, or CPC C) is supplied to each clutch by the shift valve activated. The powertrain control module (PCM) computes the actual ratio of mainshaft and countershaft revolutions. If a difference between the actual ratio and the commanded gear occurs when shifting to each gear position, a malfunction in the A/T clutch pressure control solenoid valve, the shift solenoid valve, or the hydraulic system is detected and a DTC is stored.

Hydraulic pressure to each clutch is controlled by the shift valve. The shift valve activates according to the ON/OFF status of shift solenoid valves A, B, C, and E. Hydraulic pressure supply in D position is shown above. The line pressure or the clutch pressure control pressure (CPC A, CPC B, or CPC C) is supplied to each clutch by the shift valve activated. The powertrain control module (PCM) computes the actual ratio of mainshaft and countershaft revolutions. If a difference between the actual ratio and the commanded gear occurs when shifting to each gear position, a malfunction in the shift solenoid valve or the hydraulic system is detected and a DTC is stored.

Hydraulic pressure to each clutch is controlled by the shift valve. The shift valve activates according to the ON/OFF status of shift solenoid valves A, B, C, and E. Hydraulic pressure supply in D position is shown above. The line pressure or the clutch pressure control pressure (CPC A, CPC B, or CPC C) is supplied to each clutch by the shift valve activated. The powertrain control module (PCM) computes the actual ratio of mainshaft and countershaft revolutions. If a difference between the actual ratio and the commanded gear occurs when shifting to each gear position, a malfunction in the A/T clutch pressure control solenoid valve, the shift solenoid valve, or the hydraulic system is detected and a DTC is stored.

Hydraulic pressure to each clutch is controlled by the shift valve. The shift valve activates according to the ON/OFF status of shift solenoid valves A, B, C, and E. Hydraulic pressure supply in D position is shown above. The line pressure or the clutch pressure control pressure (CPC A, CPC B, or CPC C) is supplied to each clutch by the shift valve activated. The powertrain control module (PCM) computes the actual ratio of mainshaft and countershaft revolutions. If a difference between the actual ratio and the commanded gear occurs when shifting to each gear position, a malfunction in the A/T clutch pressure control solenoid valve, the shift solenoid valve, or the hydraulic system is detected and a DTC is stored.

When the air/fuel ratio (A/F) sensor (sensor 1) is properly connected to the engine wire harness, but not installed in the exhaust pipe, the A/F feedback is not performed properly even if the A/F sensor is active after starting the engine. Thus, the exhaust emissions increase.

When the A/F sensor output stays out of the normal range after the A/F sensor becomes active, the engine control module (ECM)/powertrain control module (PCM) detects that the A/F sensor is not properly installed and a DTC is stored.

The barometric pressure (BARO) sensor is built into the engine control module (ECM)/powertrain control module (PCM) and monitors atmospheric pressure. When the throttle valve is wide open, the manifold absolute pressure (MAP) sensor output is nearly equal to the BARO sensor output. Making use of this characteristic, a malfunction can be detected in the BARO sensor output.

If the throttle position is beyond a value stored in the ECM/PCM that is used to detect. wide-open throttle,. and if the difference between the MAP sensor output and the BARO sensor output is equal to or greater than a set value, a malfunction in the BARO sensor output is detected and a DTC is stored.

The barometric pressure (BARO) sensor is built into the engine control module (ECM)/powertrain control module (PCM), and it monitors atmospheric pressure. The ECM/PCM estimates appropriate intake airflow from the manifold absolute pressure (MAP) sensor output voltage and BARO sensor output voltage. If the BARO sensor output voltage is a specified value or less, the ECM/PCM detects a malfunction and a DTC is stored.

The barometric pressure (BARO) sensor is built into the engine control module (ECM)/powertrain control module (PCM), and it monitors atmospheric pressure. The ECM/PCM estimates appropriate intake airflow from the manifold absolute pressure (MAP) sensor output voltage and BARO sensor output voltage. If the BARO sensor output voltage is a specified value or more, the ECM/PCM detects a malfunction and a DTC is stored.

The air/fuel ratio (A/F) sensor (sensor 1) is installed in the exhaust system and detects oxygen content in the exhaust gas. The A/F sensor transmits a signal to the engine control module (ECM)/powertrain control module (PCM). A heater for the sensor element is embedded in the A/F sensor (sensor 1). It heats the sensor to stabilize and speed up the detection of oxygen content. The increase in current through the heater levels off as the voltage applied to the electrode reaches a certain range because the amount of oxygen that goes through the diffusion layer is limited. The current is proportional to oxygen content in the exhaust gas, so the air/fuel ratio is detected by the measurement of the current. The ECM/PCM compares a set target air/fuel ratio with the detected air/fuel ratio and controls the fuel injection duration.

If the A/F sensor (sensor 1) voltage is low, the air/fuel ratio is lean, and the ECM/PCM uses A/F feedback control to issue a Rich command. If the A/F sensor (sensor 1) voltage is high, the air/fuel ratio is rich, and the ECM/PCM uses A/F feedback control to issue a Lean command.

If the element is not activated or the ECM/PCM terminal voltage is a set value or less for a set time when power is applied to the A/F sensor (sensor 1) heater, a malfunction is detected and a DTC is stored.

The air/fuel ratio (A/F) sensor (sensor 1) is installed in the exhaust system and detects oxygen content in the exhaust gas. The A/F sensor transmits a signal to the engine control module (ECM)/powertrain control module (PCM). A heater for the sensor element is embedded in the A/F sensor (sensor 1). It heats the sensor to stabilize and speed up the detection of oxygen content. The increase in current through the heater levels off as the voltage applied to the electrode reaches a certain range because the amount of oxygen that goes through the diffusion layer is limited. The current is proportional to oxygen content in the exhaust gas, so the air/fuel ratio is detected by the measurement of the current. The ECM/PCM compares a set target air/fuel ratio with the detected air/fuel ratio and controls the fuel injection duration.

If the A/F sensor (sensor 1) voltage is low, the air/fuel ratio is lean, and the ECM/PCM uses A/F feedback control to issue a Rich command. If the A/F sensor (sensor 1) voltage is high, the air/fuel ratio is rich, and the ECM/PCM uses A/F feedback control to issue a Lean command.

If the element is not activated or the ECM/PCM terminal voltage is a set value or less for a set time when power is applied to the A/F sensor (sensor 1) heater, a malfunction is detected and a DTC is stored.

The secondary HO2S detects the oxygen concentration in the exhaust gas downstream of the three-way catalyst (TWC). The sensor output voltage characteristics are similar to the air/fuel ratio (A/F) sensor. The oxygen concentration is detected after the TWC during fuel feedback control using the A/F sensor, and it optimizes the fuel feedback control to maximize the effect of the TWC. If, after current is applied to the secondary HO2S heater, the secondary HO2S does not fluctuate and the output is stuck within the specified area, a malfunction is detected and a DTC is stored.

The secondary HO2S detects the oxygen concentration in the exhaust gas downstream of the three-way catalyst (TWC). The sensor output voltage characteristics are similar to the air/fuel ratio (A/F) sensor. The oxygen concentration is detected after the TWC during fuel feedback control using the A/F sensor, and it optimizes the fuel feedback control to maximize the effect of the TWC. If, after current is applied to the secondary HO2S heater, the secondary HO2S does not fluctuate and the output is stuck within the specified area, a malfunction is detected and a DTC is stored.

The positive crankcase ventilation (PCV) system reduces hydrocarbons (HC). The PCV system recirculates the unburned air/fuel mixture (blow-by vapor) into the intake manifold where it is drawn into the engine and burned, thus reducing HC. If the PCV hose comes off while air is supplied mainly via the idle air control (IAC) valve with the throttle closed, the amount of air supplied to the engine is considerably more than the amount of air the IAC valve supplies.

The engine control module (ECM)/powertrain control module (PCM) estimates the amount of air supplied to the engine while the throttle valve is fully closed, and if the estimated amount is more than the upper limit, it detects a malfunction and a DTC is stored.

The fuel tank pressure (FTP) sensor output indicates about atmospheric pressure 0 kPa (0 in.Hg, 0 mmHg) before purge starts since the evaporative emission (EVAP) canister vent shut valve is normally open (open to the atmosphere). The sensor indicates a negative pressure value (vacuum) during purging.

When the FTP sensor indicates vacuum after starting the engine, there is the possibility of an FTP sensor zero point shift failure or an EVAP canister vent shut valve stuck closed failure. So the engine control module (ECM)/powertrain control module (PCM) monitors the FTP sensor output after purge starts. The ECM/PCM detects a malfunction of the EVAP canister vent shut valve if the output indicates excessive vacuum.

However, if the fuel tank internal pressure is below the specified value (excessive vacuum is detected) when starting the engine, the malfunction detection should be done as follows because it is difficult to distinguish the FTP sensor range problem (P1454) from the EVAP canister vent shut valve stuck closed (P2422).

1. If neither Temporary DTC (P1454 nor P2422) is stored, both DTCs are stored.
2. If both Temporary DTCs (P1454 and P2422) are stored and excessive vacuum is detected, both DTCs are stored.
3. If either Temporary DTC (P1454 or P2422) is stored and excessive vacuum is detected, the ECM/PCM stores the DTC of the Temporary DTC that was stored.

The engine control module (ECM)/powertrain control module (PCM) has a built-in ignition off timer that measures the duration of time from ignition off to the next ignition on. The measured duration is used for evaporative emission (EVAP) leak detection and temperature assumption of the catalytic converter.

The CPU in the ECM/PCM accesses the ignition off timer when reading the measured duration. When the access process fails, a malfunction is detected and a DTC is stored. When an abnormality is found in the read data, a malfunction is detected and a DTC is stored.

The VTEC system activates the rocker arm oil control solenoid (VTEC solenoid valve) by command from the engine control module (ECM)/powertrain control module (PCM), and it charges/discharges the hydraulic circuit of the VTEC mechanism that switches valve timing between Low and High. The ECM/PCM monitors oil pressure in the hydraulic circuit of the VTEC mechanism using the rocker arm oil pressure switch (VTEC oil pressure switch) downstream of the rocker arm oil control solenoid (VTEC solenoid valve). If there is a difference between the oil pressure condition in the hydraulic circuit that is determined by the ECM/PCM command and the oil pressure condition that is determined by the status of the rocker arm oil pressure switch (VTEC oil pressure switch), the system is considered faulty, and a DTC is stored.

The VTEC system activates the rocker arm oil control solenoid (VTEC solenoid valve) by command from the engine control module (ECM)/powertrain control module (PCM), and it charges/discharges the hydraulic circuit of the VTEC mechanism that switches valve timing between Low and High. The ECM/PCM monitors oil pressure in the hydraulic circuit of the VTEC mechanism using the rocker arm oil pressure switch (VTEC oil pressure switch) downstream of the rocker arm oil control solenoid (VTEC solenoid valve). If there is a difference between the oil pressure condition in the hydraulic circuit that is determined by the ECM/PCM command and the oil pressure condition that is determined by the status of the rocker arm oil pressure switch (VTEC oil pressure switch), the system is considered faulty, and a DTC is stored.

The VTEC system activates the rocker arm oil control solenoid (VTEC solenoid valve) by command from the engine control module (ECM)/powertrain control module (PCM), and it charges/discharges the hydraulic circuit of the VTEC mechanism that switches valve timing between Low and High. If the return signal is OFF (Low) when the ECM/PCM outputs the ON (High) signal to the rocker arm oil control solenoid (VTEC solenoid valve), the ECM/PCM detects a malfunction and a DTC is stored.

The VTEC system activates the rocker arm oil control solenoid (VTEC solenoid valve) by command from the engine control module (ECM)/powertrain control module (PCM), and it charges/discharges the hydraulic circuit of the VTEC mechanism that switches valve timing between Low and High. If the return signal is ON (High) when the ECM/PCM outputs the OFF (Low) signal to the rocker arm oil control solenoid, the ECM/PCM detects a malfunction and a DTC is stored.

The air/fuel ratio (A/F) sensor has a linear signal output in relation to the oxygen concentration. The engine control module (ECM)/powertrain control module (PCM) computes the air/fuel ratio from A/F sensor output voltage and uses the fuel feedback control to improve exhaust emissions. The ECM/PCM monitors A/F sensor output voltage during deceleration with the throttle fully closed, and if the output voltage deviates greatly from normal oxygen concentration levels, it detects a malfunction and stores a DTC.

* Output to the scan tool exhibits a relationship between the A/F sensor output and oxygen concentration, which is opposite to the characteristic shown in the graph. That is, a deviation toward the rich side increases the output voltage and one toward the lean side decreases the output voltage as the stoichiometric ratio is 0.