Pgm-Fi System (Gx): Other Honda Civic GA

Fuel injector Timing and Duration

The PCM contains memories for the basic discharge durations at various engine speeds and manifold air flow rates. 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.

Idle Air Control

Idle Air Control Valve (IAC Valve)

When the engine is cold, the A/C compressor is on, the transmission is in gear, the brake pedal is depressed, the P/S load is high, or the alternator is charging, the PCM controls current to the IAC Valve to maintain the correct idle speed.

Ignition Timing Control

The PCM contains data for basic ignition timing at various engine speeds and manifold air flow rates. Ignition timing is also adjusted for engine coolant temperature.

Other Control Functions

1. Starting Control When the engine is started, the PCM and injector control module provides a rich mixture by increasing fuel injector duration.
2. Fuel pressure regulator shut-off solenoid valve/fuel tank internal solenoid valve control When the ignition switch is initially turned on, the PCM supplies ground to the PGM-FI main relay that supplies current to the fuel pressure regulator shut-off solenoid valve/fuel tank internal solenoid valve for two seconds to pressurize the fuel system. When the engine is running, the PCM supplies ground to the PGM-FI main relay that supplies current to the fuel pressure regulator shut-off solenoid valve/fuel tank internal solenoid valve. When the engine is not running and the ignition is on, the PCM cuts ground to the PGM-FI main relay which cuts current to the fuel pressure regulator shut-off solenoid valve/fuel tank internal solenoid valve.
3. 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 1,000 RPM. Fuel cut-off action also takes place when engine speed exceeds 6,900 RPM, regardless of the position of the throttle valve, to protect the engine from over-revving.
4. A/C Compressor Clutch Relay When the PCM receives a demand for cooling from the air conditioning system, it delays the compressor from being energized, and enriches the mixture to assure smooth transition to the A/C mode.
5. Exhaust Gas Recirculation (EGR) Control Solenoid Valve. When EGR is required for control of oxides of nitrogen (NOx) emissions, the PCM controls the EGR valve.
6. Alternator Control The system controls the voltage generated at the alternator in accordance with the electrical load and driving mode, which reduces the engine load to improve the fuel economy.

PCM Fail-safe/Back-up Functions

1. Fail-safe Function When an abnormality occurs in a signal from a sensor, the PCM ignores that signal and assumes a pre-programmed value for that sensor that allows the engine to continue to run.
2. Back-up Function When an abnormality occurs in the PCM itself, the fuel injectors are controlled by a back-up circuit independent of the system in order to permit minimal driving.
3. Self-diagnosis Function [Malfunction Indicator Lamp (MIL)] When an abnormality occurs in a signal from a sensor, the PCM supplies ground for the MIL and stores the DTC in erasable memory. When the ignition is initially turned ON (II), the PCM supplies ground for the MIL for two seconds to check the MIL bulb condition.
4. Low fuel Indicator light The PCM lights the low fuel indicator light and informs the driver that the fuel level is low. The PCM calculates the gas quantity in the fuel tank by using the fuel pressure value detected by the fuel tank pressure sensor and the fuel temperature value detected by the fuel tank temperature sensor, and outputs the signal to the gauge assembly. When the PCM detects a malfunction of the fuel tank pressure sensor and/or fuel tank temperature sensor, the PCM blinks the low fuel indicator light and causes the fuel gauge to read empty. When the PCM detects a gas leak, the PCM blinks the low fuel indicator light and reduces the fuel meter to 0. If the engine is stopped while the low fuel indicator light is blinking, the engine will not start until the PCM is reset.
5. Two Trip Detection Method To prevent false indications, the Two Trip Detection Method is used for the HO2S, fuel metering-related, idle control system, ECT sensor and EGR system self-diagnostic functions. When an abnormality occurs, the PCM stores it in its memory. When the same abnormality recurs after the ignition switch is turned OFF and ON (II) again, the PCM informs the driver by lighting the MIL. However, to ease troubleshooting, this function is cancelled when you jump the service check connector. The MIL will then blink immediately when an abnormality occurs.
6. Two (or Three) Driving Cycle Detection Method A "Driving Cycle" consists of starting the engine, beginning closed loop operation, and stopping the engine. If misfiring that increases emissions is detected during two consecutive driving cycles, or TWC deterioration is detected during three consecutive driving cycles, the PCM turns the MIL on. However, to ease troubleshooting, this function is cancelled when you jump the service check connector. The MIL will then blink immediately when an abnormality occurs.

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Possible Cause

1. ECT sensor deterioration
2. Malfunction in the cooling system

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Primary Heated Oxygen Sensor (Primary HO2S) (Sensor 1)

The Heated Oxygen Sensor (HO2S) detects the oxygen content in the exhaust gas and signals the PCM. In operation, the PCM receives the signals from the sensor and varies the duration during which fuel is injected. To stabilize the sensor's output, the sensor has an internal heater. The Primary HO2S (Sensor 1) is installed in the exhaust manifold.

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1. Primary HO2S (Sensor 1) Deterioration
2. Primary HO2S Heater (Sensor 1) Deterioration
3. Exhaust system leakage

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DTC P0171: System Too Lean

1. Fuel Feed Line clogged, leaking
2. Fuel Pressure Regulator stuck open
3. Fuel Filter clogged
4. Fuel Injector clogged, air inclusion
5. Fuel doesn't meet Owner's Manual spec.
6. Primary HO2S (Sensor 1) deteriorated
7. EGR System malfunction (too much flow)
8. Valve Clearance
9. Exhaust leak
10. Fuel Pressure Sensor range/performance

DTC P0172: System Too Rich

1. Fuel Pressure Regulator clogged, stuck closed
2. Fuel Injector leaking
3. Fuel doesn't meet Owner's Manual spec.
4. Primary HO2S (Sensor 1) deteriorated
5. EGR System insufficient flow
6. Valve Clearance
7. Fuel Pressure Sensor range/performance

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1. Fuel injector clogging, fuel leakage, air leakage
2. Fuel injector circuit open or shorted
3. Injector control module
4. Spark plug carbon deposits, fouling, malfunction
5. Ignition wires open, leaking
6. Distributor malfunction
7. Compression low
8. Valve clearance out of spec
9. VTEC system malfunction
10. HO2S
11. HO2S circuit

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1. Fuel line clogging, blockage, leakage
2. Fuel filter clogging
3. Fuel pressure regulator stuck open
4. EGR system malfunction
5. Distributor malfunction
6. Ignition control module malfunction
7. Valves carbon deposit
8. Compression low
9. VTEC system malfunction
10. Fuel does not meet Owner's Manual spec, lack of fuel
11. HO2S
12. HO2S circuit
13. Injector control module

Fuel Tank Pressure Sensor

The fuel tank pressure sensor is located on the fuel joint block, and it detects fuel tank pressure. This signal is used to calculate the fuel injection duration in the tank and to detect any leakage.

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