EGR System Honda Accord III

DESCRIPTION

Honda uses exhaust gas recirculation (EGR) on all models to reduce oxides of nitrogen (NOx) emissions. The system includes a special intake manifold and cylinder head, EGR valve, EGR control valves, EGR switch and EGR control solenoid valves.

OPERATION

The EGR system operates only when the engine is at normal operating temperature and only while accelerating or cruising. The vacuum control signal is carburetor ported vacuum. A thermosensor eliminates EGR when engine coolant is below normal operating temperature.

During vehicle deceleration, manifold vacuum rises and turns on EGR control switch. The EGR control solenoid valve closes and cuts off EGR flow. Vacuum is provided to EGR control switch only above 15 MPH, when the speed sensor opens the throttle opener solenoid valve.

EGR control valves A and B use a ported vacuum signal to control a manifold vacuum flow large enough to operate the EGR valve. With this system, the EGR valve is operated by a signal proportional to airflow through carburetor venturi, ensuring correct EGR flow.

EGR control valves A and B receive vacuum from thermovalve C.

EGR VALVE

1. Start engine. Disconnect vacuum hose from EGR valve. Connect a vacuum pump to EGR valve.
2. Apply 6 in. Hg of vacuum to EGR valve. Ensure vacuum holds steady. Engine should die. If vacuum does not hold, replace EGR valve. If engine does not die, check EGR valve and ports for blockage.

THERMOSENSOR

1. On carbureted models, remove leads from thermosensor. On a cold engine, below 158°F (70°C), there should be no continuity. There should be continuity above 158°F (70°C).

Switch A

Disconnect No. 4 hose from control box at vacuum hose manifold. Connect vacuum pump to hose. Check for continuity between White/Blue wire terminal of control box connector and ground. There should be continuity when more than 1.2 in. Hg vacuum is applied to switch. There should be no continuity when vacuum is released.

Switch B

Disconnect No. 7 hose from control box at vacuum hose manifold. Connect vacuum pump to hose. Check for continuity between Black/Yellow wire and Blue/White wire terminals of control box connector. There should be no continuity when more than 1.2 in. Hg vacuum is applied to switch. There should be continuity when vacuum is released.

Switch C

Disconnect No. 14 hose from control box at vacuum hose manifold. Connect vacuum pump to hose. Remove control box from firewall and remove control box cover. Check for continuity between vacuum switch C wire terminals. There should be continuity when more than 3.9 in. Hg vacuum is applied to switch. There should be no continuity when vacuum is released.

CONTROL UNIT CONNECTORS

Check for voltage at control unit connector (Blue and Black/Yellow wires) with ignition on. If there is no voltage at Black/Yellow wire, check fuse and wiring. If there is no voltage at Blue wire, check wire between ignition coil and control unit. Check Black wire for continuity between control unit and ground. There should be continuity.

SPEED SENSOR

1. Raise and support front of vehicle. Connect voltmeter probe into Yellow wire terminal at control box No. 1 connector. Connect negative probe to ground. Start engine.
2. Select second gear (man. trans.) or position "2" (auto. trans.) and accelerate slowly, while observing voltmeter. Voltage should be battery voltage below 10 MPH and no voltage above 20 MPH. If so, sensor is okay. If not, install a new sensor and retest.
3. If there is no voltage during speed sensor test, check for bad electrical connection, fuse or faulty speed sensor. Repair or replace as necessary and retest.

COLD ENGINE

Note. Engine coolant temperature must be below thermovalve C set temperature of 158°F (70°C).

Disconnect vacuum hose from EGR valve and connect vacuum gauge to hose. Start engine and raise engine speed to 3000 RPM. Vacuum should not be available to EGR valve. If vacuum is not available to EGR valve, proceed to HOT ENGINE test. If vacuum is available, replace thermovalve A and retest.

Carbureted Models

1. Disconnect vacuum hose from EGR valve and connect vacuum gauge to hose. Remove control box from firewall and remove cover attaching screws. On all models, vacuum and voltage should be as shown in EGR SYSTEM TEST table. EGR SYSTEM TEST Condition No. Engine Condition EGR Valve Vacuum 1 Idle No 2 3000 RPM 2-6 in. Hg 3 3000 RPM (1) Less Than 2 in. Hg 4 Hard Acceleration 2-6 in. Hg 5 Deceleration No (1) With EGR bleed plugged.
2. If there is no vacuum available for conditions No. 2 and No. 4, check for vacuum at inlet and outlet of thermovalve C. If there is no vacuum at outlet, replace thermovalve. If no vacuum at inlet, check vacuum line routing and repair or replace. Clean and retest.
3. If vacuum is available on condition No. 1 or vacuum is greater than 2 in. Hg on condition No. 3, replace EGR control solenoid valve. Ensure vacuum hoses are routed properly.

Scheme 11

1. Check self-diagnostic light No. 12. If light is on, check No. 16 and No. 24 vacuum hoses for loose connections, before proceeding with test. Start engine and warm-up to normal operating temperature (cooling fan comes on).
2. Disconnect vacuum hose from top of EGR valve. Connect vacuum pump/gauge to EGR valve. Plug EGR solenoid valve lower hose in No. 2 control box. Measure vacuum at idle. If vacuum reading stabilizes at 5.9-9.8 in. Hg, constant vacuum control valve is okay.
3. If vacuum reading is outside 6-10 in. Hg, check hose between intake manifold and vacuum gauge for clogging, kinking or leakage. If hose is okay, replace CVC valve and retest. Unplug EGR solenoid valve lower hose.
4. Measure vacuum at idle. If vacuum is below 1.2 in. Hg, EGR control solenoid valve is okay. If vacuum is more than 1.2 in. Hg, check airflow hose to EGR control solenoid valve for blockage. If hose is okay, replace EGR control solenoid valve and retest.
5. Disconnect No. 21 vacuum hose from between throttle body and intake air pressure sensor. Plug vacuum fitting at throttle body. Connect vacuum pump to No. 21 vacuum hose and apply 12 in. Hg vacuum. Raise engine idle speed to 2400 RPM. Feel operation of EGR control solenoid valve with your fingers.
6. If EGR control solenoid valve is operating, system is okay. If EGR solenoid valve is not operating, check harnesses between EGR control solenoid valve and ECU (Blue/Red and Black/Yellow wires) for open or short circuits. If harness is okay, check EGR control solenoid valve.
7. If EGR control solenoid valve is working, check EGR valve and lift sensor. To check EGR control solenoid valve, disconnect wiring harness from No. 2 control box. Disconnect No. 10 vacuum hose from vacuum hose manifold.
8. Ensure there is airflow through hose. If there is no airflow, replace EGR control solenoid valve and retest. Connect positive lead of 12 volt battery to Black/Yellow terminal of No. 2 control box coupler. Connect negative lead to Blue/Red terminal.
9. Pump air into No. 10 hose, making sure there is no airflow. If air is flowing through hose, replace EGR control solenoid valve and retest. (Scheme 11) (Scheme 11): Testing EGR Control Solenoid Valve
10. When testing EGR valve, start engine and let it idle. Disconnect EGR valve upper hose. Connect vacuum pump to EGR valve. Apply 6 in. Hg vacuum. If vacuum remains steady and engine dies, EGR valve is working properly. If vacuum does not remain steady and engine does not die, replace EGR valve and retest.
11. If vacuum remains steady but engine does not die, remove EGR valve. Check EGR valve and manifold for blockage. Clean or replace as necessary and retest.
12. To test EGR valve lift sensor, connect system checker harness between ECU and wiring harness connector. Turn ignition on. Measure voltage between terminal C13 of system checker harness (Red/Blue wire) and terminal C12 (Green/White wire).
13. Voltage should be 1.0-1.4 volts. If voltage reading is 1.0-1.4 volts, substitute a known-good ECU. Retest EGR system. If EGR still does not operate properly, replace EGR valve lift sensor. If voltage reading is not 1.0-1.4 volts, turn ignition off.
14. Check for open or short circuit in Red/Blue and Green/White wires between EGR valve lift sensor and ECU. Repair or replace harness as necessary. If harness checks okay, turn ignition on. Connect vacuum pump to upper hose of EGR valve.
15. Apply vacuum to valve and measure voltage between terminal C8 (Red/Blue wire) of system checker harness and terminal C12 (Green/White wire). Voltage reading should be 1.2-3.8 volts. If voltage reading is not within specifications, replace faulty EGR valve lift sensor.
16. If voltage reading is within specifications, substitute a known good ECU. Retest EGR system. If EGR system still does not operate properly, replace EGR valve lift sensor.