Intermittent Failures
The term "intermittent failure" means a system may have had a failure, but it checks OK now. If the Malfunction Indicator Lamp (MIL) on the dash does not come on, check for poor connections or loose wires at all connectors related to the circuit that you are troubleshooting.
Opens and Shorts
"Open" and "Short" are common electrical terms. An open is a break in a wire or at a connection. A short is an accidental connection of a wire to ground or to another wire. In simple electronics, this usually means something won't work at all. With complex electronics such as ECMs/PCMs, this can sometimes mean something works, but not the way it's supposed to.
Electronic Control System
The functions of the fuel and emission control systems are managed by the engine control module (ECM) on vehicles with manual transmissions or the powertrain control module (PCM) on vehicles with automatic transmissions.
Fail-safe Function
When an abnormality occurs in the signal from a sensor, the ECM/PCM ignores that signal and assumes a preprogrammed value for that sensor that allows the engine to continue to run.
Back-up Function
When an abnormality occurs in the ECM/PCM, the injectors are controlled by a back-up circuit independent of the system in order to permit minimal driving.
Two Driving Cycle Detection Method
To prevent false indications, the "two driving cycle detection method" is used for some self-diagnostic functions. When an abnormality occurs, the ECM/PCM stores it in its memory. When the same abnormality recurs after the ignition switch is turned OFF and ON (II) again, the ECM/PCM turns on the MIL.
ECM/PCM Data
Note. The "operating values" listed are approximate and may vary depending on the environment and the individual vehicle. Unless noted otherwise, "at idle speed" means idling with the engine completely warmed up, A/T in park or neutral, M/T in neutral position, and the A/C and all accessories turned off.
You can retrieve data from the ECM/PCM by connecting the OBD II scan tool or the Honda PGM Tester to the data link connector (DLC). The items listed in the table below conform to SAE recommended practice. The Honda PGM Tester also reads data beyond that recommended by SAE to help you find the causes of intermittent problems.
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Note. Standard battery voltage is 12 V.
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Note. Standard battery voltage is 12 V.
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Note. Standard battery voltage is 12 V.
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Note. Standard battery voltage is 12 V.
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PGM-FI System
The Programmed Fuel Injection (PGM-FI) system is a sequential multiport fuel injection system.
Air conditioning (A/C) Switch
The A/C (air conditioning) switch signals the ECM/PCM whenever there is a demand for cooling.
A/C Compressor Clutch Relay
When the ECM/PCM receives a demand for cooling from the A/C system, it delays the compressor from being energized, and enriches the mixture to assure smooth transition to the A/C mode.
Air Fuel Ratio (A/F) Sensor (F23A4 engine)
The A/F Sensor operates over a wide air/fuel range. The A/F Sensor is installed in the exhaust manifold.
Scheme 30
Alternator Control
The alternator signals the ECM/PCM during charging. The ECM/PCM then controls the voltage generated at the alternator according to the electrical load determined by the ELD (Electrical Load Detector) and driving mode. This reduces engine load to improve fuel economy.
Barometric Pressure (BARO) Sensor
The barometric pressure sensor is inside the ECM/PCM. It converts atmospheric pressure into a voltage signal that modifies the basic duration of the fuel injection discharge.
Crankshaft Position (CKP) & Top Dead Center (TDC) Sensors
The CKP sensor determines fuel injection timing and ignition timing for each cylinder, and also detects engine speed. The TDC sensor determines ignition timing at start-up and when crankshaft position signal is abnormal.
Scheme 31
Cylinder Position (CYP) Sensor
The CYP sensor inside the distributor detects the position of the No. 1 cylinder as a reference for sequential fuel injection to each cylinder.
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Engine Coolant Temperature (ECT) Sensor
The ECT sensor is a temperature dependent resistor (thermistor). The resistance of the thermistor decreases as the Engine Coolant temperature increases.
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Intake Air Temperature (IAT) Sensor
The IAT sensor is a temperature dependent resistor (thermistor). The resistance of the thermistor decreases as the intake air temperature increases.
Scheme 35
Ignition Timing Control
The ECM/PCM contains the memory for basic ignition timing at various engine speeds and manifold air flow rates. It also adjusts the timing according to engine coolant temperature. The ECM/PCM detects misfiring by using the CKP sensor to monitor fluctuations in crankshaft speed. It will then set DTCs depending on how much misfiring occurs.
Injector Timing and Duration
The ECM/PCM contains the memory for basic discharge duration at various engine speeds and manifold pressures. The basic discharge duration, after being read out from the memory, is further modified by signals sent from various sensors to obtain the final discharge duration.
By monitoring Long Term Fuel Trim, the ECM/PCM detect long term malfunctions in the fuel system and set a Diagnostic Trouble Code (DTC) if the malfunction occurs during two consecutive trips.
Knock Sensor (F23A1, F23A4 engine)
The knock control system adjusts the ignition timing for the octane rating of the gasoline used.
Scheme 36
Manifold Absolute Pressure (MAP) Sensor
The MAP sensor converts manifold absolute pressure into electrical signals to the ECM/PCM.
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Malfunction Indicator Lamp (MIL) Indication (In relation to Readiness Codes) - F23A4 engine
The vehicle has certain "readiness codes" that are part of the on-board diagnostics for the emissions systems. If the vehicle's battery has been disconnected or gone dead, if the DTCs have been cleared, or if the ECM/PCM has been reset, these codes are reset. In some states, part of the emissions testing is to make sure these codes are set to complete. If all of them are not set to complete, the vehicle may fail the test.
To check if the readiness codes are set, turn the ignition switch ON (II), but do not start the engine. The MIL will come on for 15-20 seconds. If it then goes off, the readiness codes are set. If it blinks several times, one or more readiness codes are not set to complete. To set each code, drive the vehicle or run the engine as described in the procedures to set them (see How to Set Readiness Codes ).
Primary Heated Oxygen sensor (Primary HO2S)
The primary HO2S detects the oxygen content in the exhaust gas and sends signals to the ECM/PCM which varies the duration of fuel injection accordingly. To stabilize its output, the sensor has an internal heater. The primary HO2S is installed in the exhaust manifold. By controlling the air fuel ratio with primary HO2S and secondary HO2S, the deterioration of the primary HO2S can be evaluated by its feedback period. When the feedback period exceeds a certain value during stable driving conditions, the sensor is considered deteriorated and the ECM/PCM sets a DTC.
Scheme 38
Secondary Heated Oxygen sensor (Secondary HO2S)
The secondary HO2S detects the oxygen content in the exhaust gas downstream of the Three Way Catalytic Converter (TWC) and sends signals to the ECM/PCM which varies the duration of fuel injection accordingly. To stabilize its output, the sensor has an internal heater. The secondary HO2S is installed in the TWC.
Scheme 39
Throttle Position (TP) Sensor
The TP sensor is a potentiometer connected to the throttle valve shaft. As the throttle position changes, the sensor varies the signal voltage to the ECM/PCM. The TP sensor is not replaceable apart from the throttle body.
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Vehicle Speed Sensor (VSS) (M/T)
The speed sensor is driven by the differential. It generates a pulsed signal from an input of 5 volts. The number of pulses per minute increases/decreases with the speed of the vehicle.
Intake Air System
Refer to the Intake Air System Diagram to see the functional layout of the system.
Throttle Body
The throttle body is a single-barrel side draft type. The lower portion of the throttle valve is heated by engine coolant from the cylinder head. The idle adjusting screw, which increases/decreases bypass air, is located on the top of the throttle body.
Scheme 41
Idle Control System
When the engine is cold, the A/C compressor is on, the transmission is in gear, the brake pedal is pressed, the P/S load is high, or the alternator is charging, the ECM/PCM controls current to the IAC valve to maintain the correct idle speed. Refer to the System Diagram to see the functional layout of the system.
Idle Air Control (IAC) Valve
To maintain the proper idle speed, the IAC valve changes the amount of air bypassing the throttle body in response to an electrical signal from the ECM/PCM.
Scheme 42
Power Steering Pressure (PSP) Switch
The PSP switch signals the ECM/PCM when the power steering load is high.
Starter (Ignition) Switch
The starter switch signals the ECM/PCM when the engine is cranking.
Brake Pedal Position Switch
The brake pedal position switch signals the ECM/PCM when the brake pedal is pressed.
Fuel Pump Control
When the ignition is turned on, the ECM/PCM grounds the PGM-FI main relay which feeds current to the fuel pump for 2 seconds to pressurize the fuel system. With the engine running, the ECM/PCM grounds the PGM-FI main relay and feeds current to the fuel pump. When the engine is not running and the ignition is on, the ECM/PCM cuts ground to the PGM-FI main relay which cuts current to the fuel pump.
Fuel Cut-off Control
During deceleration with the throttle valve closed, current to the fuel injectors is cut off to improve fuel economy at speeds over 1,100 RPM.
Fuel cut-off action also occurs when engine speed exceeds 6,500 RPM, regardless of the position of the throttle valve, to protect the engine from over-revving. On A/T models, when the vehicle is stopped, the PCM cuts the fuel at engine speeds over 5,000 RPM.
PGM-FI Main Relay
The PGM-FI relay contains two separate relays. One is energized whenever the ignition is on which supplies battery voltage to the ECM/PCM, power to the fuel injectors, and power for the second relay. The second relay is energized to supply power to the fuel pump for two seconds when the ignition is switched ON (II), and when the engine is running.
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Exhaust Gas Recirculation (EGR) System
Refer to the System Diagram to see the functional layout of the system.
EGR Valve
The EGR valve is designed to lower peak combustion temperatures and reduce oxides of nitrogen emissions (NOx) by recirculating exhaust gas through the intake manifold and into the combustion chambers.
Positive Crankcase Ventilation (PCV) System
The PCV valve prevents blow-by gasses from escaping into the atmosphere by venting them into the intake manifold.
Scheme 44
Evaporative Emission (EVAP) Control System
Refer to the System Diagram to see the functional layout of the system.
EVAP Canister
The EVAP canister temporarily stores fuel vapor from the fuel tank until it can be purged back into the engine and burned.
EVAP Canister Purge Valve
When the engine coolant temperature is below 167°F (75°C), the ECM/PCM turns off the EVAP canister purge valve which cuts vacuum to the EVAP canister.
Fuel Tank Pressure (FTP) Sensor
The FTP sensor converts fuel tank absolute pressure into an electrical input to the ECM/PCM.
Scheme 45
Three Way Catalytic Converter (TWC)
The TWC converts hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) in the exhaust gas to carbon dioxide (CO2), dinitrogen (N2), and water vapor.
Scheme 46
Intake Air System Diagram
This system supplies air for engine needs. A resonator in the air intake duct provides additional silencing as air is drawn into the system.
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Idle Control System Diagram
The idle speed of the engine is controlled by the Idle Air Control (IAC) valve
Scheme 48
- After the engine starts, the IAC valve opens for a certain time. The amount of air is increased to raise the idle speed by about 150-300 RPM.
- When the engine coolant temperature is low, the IAC valve is opened to obtain the proper fast idle speed. The amount of bypassed air is thus controlled in relation to engine coolant temperature.
Exhaust Gas Recirculation (EGR) System Diagram
The EGR system reduces oxides of nitrogen (NOx) emissions by recirculating exhaust gas through the EGR valve and the intake manifold into the combustion chambers. The ECM/PCM memory includes the ideal EGR valve lift for varying operating conditions.
The EGR valve position sensor detects the amount of EGR valve lift and sends it to the ECM/PCM. The ECM/PCM then compares it with the ideal lift in its memory (based on signals sent from other sensors). If there is any difference between the two, the ECM/PCM controls current to the EGR valve.
Scheme 49
Evaporative Emission (EVAP) Control Diagram
The EVAP controls minimize the amount of fuel vapor escaping to the atmosphere. Vapor from the fuel tank is temporarily stored in the EVAP canister until it can be purged from the canister into the engine and burned.
Scheme 50
- The EVAP canister is purged by drawing fresh air through it and into a port on the intake manifold. The purging vacuum is controlled by the EVAP canister purge valve, which is open whenever engine coolant temperature is above 167°F (75°C).
- When vapor pressure in the fuel tank is higher than the set value of the EVAP two way valve, the valve opens and regulates the flow of fuel vapor to the EVAP control canister.
- During refueling, the fuel tank vapor control valve opens with the pressure in the fuel tank, and feeds the fuel vapor to the EVAP canister.
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The vehicle has certain "readiness codes" that are part of the on-board diagnostics for the emissions systems. If the vehicle's battery has been disconnected or gone dead if the DTCs have been cleared, or if the ECM/PCM has been reset, these codes are reset. In some states, part of the emissions testing is to make sure these codes are set to complete. If all of them are not set to complete, the vehicle may fail the test.
To check if the readiness codes are set, turn the ignition switch ON (II), but do not start the engine. The MIL will come on for 15-20 seconds. If it then goes off, the readiness codes are set. If it blinks several times, one or more readiness codes are not set to complete. To set each code, drive the vehicle or run the engine as described in the following procedures.
Air Fuel Ratio (A/F) Sensor Monitor Code
Note. Do not turn the ignition switch OFF. When the battery negative cable is disconnected, all readiness codes are cleared.
Required condition
- Ambient temperature between 20-95°F (-7-35°C).
- Connect the scan tool to the Data Link Connector (DLC).
- Start the engine. Hold it at 3,000 RPM with no load (in Park or neutral) until the radiator fan comes on.
- Let the engine idle for 5 seconds.
- Drive at a steady speed between 50-62 mph (80-100 km/h) with the transmission in D4 position for about 2 minutes.
- With the A/T in D4 position or M/T in 5th gear, decelerate from 62 mph (100 km/h) by completely releasing the throttle for at least 5 seconds. If the engine is stopped during this procedure, repeat steps 4 and 5.
- Check for the readiness code with the scan tool.
Catalytic Converter Monitor Code
Note. Do not turn the ignition switch OFF. When the battery negative cable is disconnected, all readiness codes are cleared. When the ECM/PCM is cleared with the OBD II scan tool or Honda PGM Tester, all readiness codes are cleared.
Required condition
- Ambient temperature between 20-95°F (-7-35°C).
- Connect the scan tool to the Data Link Connector.
- Start the engine. Hold it at 3,000 RPM with no load (in Park or neutral) until the radiator fan comes on.
- Drive for about 10 minutes, without stopping, on a highway. Your speed can vary.
- With the A/T in D4 position or M/T in 5th gear, drive at a steady speed between 50-60 mph (80-100 km/h) for 30 seconds.
- Repeat step 4 three times. Between each repetition, close the throttle completely for 1-2 seconds. If the engine is stopped during this part of the procedure, repeat steps 3, 4, and 5.
- Check for the readiness code with the scan tool.
EGR Monitor Code
Note. Do not turn the ignition switch OFF. When the battery negative cable is disconnected, all readiness codes are cleared.
- Connect the scan tool to the Data Link Connector.
- Start the engine, and hold it at 3,000 RPM with no load (in Park or neutral) until the radiator fan comes on.
- Drive at a steady speed with the transmission in D4 position between 50-62 mph (80-100 km/h) for more than 10 seconds.
- With the A/T in D4 position or M/T in 5th gear, decelerate from 62 mph (100 km/h) by completely releasing the throttle for at least 5 seconds. If the engine is stopped during this procedure, repeat steps 3 and 4.
- Check for the readiness code with the scan tool.
EVAP Leak Monitor Code
Note. When the battery negative cable is disconnected, all readiness codes are cleared. When the ECM/PCM is cleared with the OBD II scan tool or Honda PGM Tester, all readiness codes are cleared. If the engine is stopped between step 6 and 16, do the entire procedure again.
- Make sure the gasoline level is 60-90 percent of fuel tank capacity (not full).
- Turn the ignition switch OFF.
- Let the vehicle sit more than 8 hours.
- Make sure the outside temperature is 20-95°F (-7-35°C).
- Connect the scan tool to the Data Link Connector.
- Start the engine, and drive for about 15 minutes.
- Keep the vehicle at a steady speed between 50-70 mph (80-114 km/h), without moving the accelerator pedal, for about 1 minute.
- Stop the vehicle (do not stop engine).
- Repeat step 7 and 8 two more times.
- Check for the readiness code with the scan tool. If the readiness code does not set, go to step 11.
- When ambient temperature is less than 32°F (0°C), hold the engine at 3,000 RPM with no load (in Park or neutral) until the radiator fan comes on.
- Remove the fuel fill cap, then reinstall it.
- Drive for about 20 minutes on a highway.
- Keep the vehicle at a steady speed between 50-70 mph (80-114 km/h) without moving the accelerator pedal, for about 1 minute.
- Stop the vehicle (do not stop the engine).
- Repeat steps 14 and 15 two more times.
- Check for the readiness code with the scan tool.
HO2S Monitor Code
Note. Do not turn the ignition switch OFF. When the battery negative cable is disconnected, all readiness codes are cleared.
Required condition
- Ambient temperature between 20-95°F (-7-35°C).
- Connect the scan tool to the Data Link Connector.
- Start the engine, and hold it at 3,000 RPM with no load (in Park or neutral) until the radiator fan comes on.
- Let the engine idle for 5 seconds.
- Drive at a steady speed between 50-62 mph (80-100 km/h) for about 2 minutes.
- With the A/T in D4 position or M/T in 5th gear, decelerate from 62 mph (100 km/h) by completely releasing the throttle for at least 5 seconds. If the engine is stopped during this procedure, repeat steps 4 and 5.
- Check for the readiness code with the scan tool.
HO2S Heater Monitor Code
Note. When the battery negative cable is disconnected, all readiness codes are cleared.
- Connect the scan tool to the Data Link Connector.
- Start the engine, and let it idle for 10 minutes.
- Check for the readiness code with the scan tool.