Engine Controls - System/component Tests Honda Accord IV

INTRODUCTION

Before testing separate components or systems, perform procedures in BASIC TESTING article in the ENGINE PERFORMANCE Section. Since many computer-controlled and monitored components set trouble codes if they malfunction, also perform procedures in TESTS W/CODES article in the ENGINE PERFORMANCE Section.

Note. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Testing individual components does not isolate shorts or opens. Use ohmmeter to isolate wiring harness shorts or opens.

Intake Control Diaphragm

Connect a vacuum pump to vacuum hose on intake control diaphragm. Apply vacuum. If diaphragm holds vacuum, intake diaphragm is okay. If vacuum is not held, check vacuum line for improper connection and disconnected hose. If hose is okay, replace intake control diaphragm.

Intake Control Solenoid Valve

1. Start engine, and allow to idle. Remove upper vacuum hose from intake control solenoid valve, and connect a vacuum gauge to solenoid valve. If vacuum is not present, go to step 2). If vacuum is present, raise engine speed to 3700 RPM. If vacuum is still present, go to step 4). If vacuum is no longer present, solenoid valve is okay.
2. Disconnect lower vacuum hose of solenoid valve from air chamber, and connect a vacuum gauge. If vacuum is present, go to next step. If vacuum is not present, check vacuum line for improper connection, cracks and blockage in hose. If vacuum line is okay, clean manifold port.
3. Disconnect 2-pin connector from intake control solenoid valve. Measure voltage between Black/Yellow (positive) terminal and White (negative) terminal. If battery voltage is not present, solenoid valve is okay. If battery voltage is present, replace intake control solenoid valve.
4. Disconnect 2-pin connector from solenoid valve. Check vacuum gauge. If vacuum is no longer present, solenoid valve is okay. If vacuum is still present, replace solenoid valve.

Ground Circuits

1. Using an ohmmeter, check for continuity to ground on appropriate ECU ground terminals. See «POWER & GROUND CIRCUITS TERMINAL IDENTIFICATION»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. (Scheme 10) Resistance should be zero ohms for each circuit. If reading is not zero ohms, repair open to ground.
2. Using a DVOM, touch negative lead of voltmeter to a good ground. Touch positive lead of voltmeter to each ground terminal. With vehicle running, voltmeter should indicate less than.1 volt. If voltmeter reading is greater than.1 volt, check for open, corrosion or loose connection on ground lead.

Scheme 10

1. Using a voltmeter, check for battery voltage between ECU power terminal and ground. See «POWER & GROUND CIRCUITS TERMINAL IDENTIFICATION»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. (Scheme 10) If battery voltage is not present, check appropriate ECU fuse in underhood fuse box. See «ECU POWER CIRCUITS FUSE IDENTIFICATION»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. If fuse is okay, check for an open in wire between underhood fuse box and appropriate ECU power circuit terminal.
2. Turn ignition switch to ON position. Using a voltmeter, check for battery voltage between appropriate ECU power circuit terminal and ground. See «POWER & GROUND CIRCUITS TERMINAL IDENTIFICATION»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. (Scheme 10) If battery voltage is not present, check appropriate fuse in underhood fuse box. See «ECU POWER CIRCUITS FUSE IDENTIFICATION»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. If fuse is okay, check for an open in wire between fuse box and appropriate ECU power circuit terminal or check for a defective ignition switch. POWER & GROUND CIRCUITS TERMINAL IDENTIFICATION Application (1) ECU Terminal Ground Circuits A23, A24, A26 & B2 Power Circuits Ignition Switch In OFF Position D1 Ignition Switch ON Position A25 & B1 (1) (Scheme 10)for terminal location identification. ECU POWER CIRCUITS FUSE IDENTIFICATION Application (1) Fuse Ignition Switch In OFF Position BACK-UP Ignition Switch ON Position ECU (1) All fuses are in underhood fuse box.

ENGINE SENSORS & SWITCHES

Note. Some test procedures require using a test harness when testing certain components or systems. Use ECU Test Harness (07LAJ-PT3010A ). (Scheme 11) Test harness must be connected between control unit and main wire harness connectors.

Scheme 11

Voltage Test

1. Connect test harness between ECU and main wire harness connectors. (Scheme 11) Disconnect "B" connector from main harness, but not from ECU. Turn ignition on. Measure voltage between terminals B5 (+) and A26 (-). (Scheme 10)
2. If voltage is approximately 5 volts, go to next step. If voltage is not as specified, substitute known good ECU, and retest. If voltage reading is now as specified, replace ECU. If voltage reading still is not as specified, check and repair wiring between A/C switch and ECU. See «WIRING DIAGRAMS»(/honda/accord/iv-1989-1993/remont/wiring-diagrams-engine-performance/#wiring-diagrams) article in the ENGINE PERFORMANCE Section.
3. Turn ignition off. Reconnect "B" connector to main harness. Turn ignition on. Momentarily connect ECU terminals A15 (+) and A26 (-) together. (Scheme 10) If clicking noise is not heard from A/C clutch, go to next step. If clicking noise is heard, start engine and turn A/C on. If A/C operates, A/C signal is present. If A/C does not operate, go to step 5).
4. Using a jumper wire, connect Red/Blue wire from A/C compressor control unit to chassis ground. See «WIRING DIAGRAMS»(/honda/accord/iv-1989-1993/remont/wiring-diagrams-engine-performance/#wiring-diagrams) article in the ENGINE PERFORMANCE Section. If clicking noise is heard from A/C clutch, repair open circuit between ECU and A/C compressor control unit. If clicking noise is not heard from A/C clutch, repair A/C system. See «A/C-HEATER SYSTEM - MANUAL»(/honda/accord/iv-1989-1993/remont/manual-hvac-system/#ac-heater-system-manual) article in the AIR CONDITIONING & HEAT Section.
5. With engine running and A/C turned on, measure voltage between terminals A15 (+) and A26 (-). (Scheme 10) If voltage reading is less than one volt, substitute a known good ECU. If A/C now functions, replace ECU. If voltage reading is greater than one volt, repair open circuit between ECU and A/C switch. See «WIRING DIAGRAMS»(/honda/accord/iv-1989-1993/remont/wiring-diagrams-engine-performance/#wiring-diagrams) article in the ENGINE PERFORMANCE Section.

ATMOSPHERIC PRESSURE (PA) SENSOR

PA sensor is built into ECU. See TESTS W/CODES article in the ENGINE PERFORMANCE Section for testing.

Resistance Test

Start engine, and warm to normal operating temperature. Disconnect sensor connector. Using an ohmmeter, measure resistance across sensor terminals. If resistance is not 200-400 ohms, replace sensor.

Functional Test

See EMISSION SYSTEMS & SUB-SYSTEMS .

Disconnect sensor connector. Using an ohmmeter, measure resistance across sensor terminals. Resistance should be as specified. See the INTAKE AIR TEMPERATURE (TA) SENSOR RESISTANCE TEST table. If resistance is not within specification, replace sensor.

INTAKE AIR TEMPERATURE (TA) SENSOR RESISTANCE TEST

1. Connect test harness between ECU and main wire harness connectors. (Scheme 11) Turn ignition switch to ON position. Measure voltage between terminals D17 (+) and D21 (-). (Scheme 10)
2. If voltage is approximately 3 volts, go to next step. If voltage is not approximately 3 volts, check wiring to sensor for continuity. If wiring is okay, replace MAP sensor.
3. Connect a vacuum pump to MAP sensor, and apply vacuum. If MAP sensor does not hold vacuum, replace sensor.

Scheme 12

1. Disconnect 4-pin connector at O2 sensor. Measure resistance between terminals A and B of sensor connector. (Scheme 12) If resistance reading is 15-20 ohms, go to next step. If resistance is not as specified, replace O2 sensor.
2. Check for continuity to ground on each terminal on O2 sensor. (Scheme 12) If continuity exists, replace O2 sensor. If continuity does not exist, go to next step.
3. Check for continuity between terminals A and C and between terminals A and D. (Scheme 12) If continuity exists in either case, replace O2 sensor. If continuity does not exist, check wiring to sensor. See «TESTS W/CODES»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-tests-wcodes) article in the ENGINE PERFORMANCE Section.

POWER STEERING (P/S) OIL PRESSURE SWITCH

1. Connect test harness between ECU and connector. (Scheme 11) Turn ignition on. Measure voltage between test harness terminals B8 (+) and A26 (-). (Scheme 10) If voltage is present, go to next step. If voltage is not present, go to step 3).
2. Disconnect 2-pin connector on P/S switch. Jumper Red wire terminal to Black wire terminal. Check voltage. If voltage is not present, replace P/S switch. If voltage is present, repair open in Red wire between positive ECU terminal B8 and P/S switch or Black wire between P/S switch and ground. (Scheme 10)
3. Start engine. Turn steering wheel slowly. Measure voltage between test harness terminals B8 (+) and A26 (-). (Scheme 10) If battery voltage is present, P/S switch signal is okay. If battery voltage is not present, go to next step.
4. Turn ignition off. Disconnect test harness "B" connector from main wire harness only, not ECU. Turn ignition switch to ON position. If battery voltage is present, go to next step. If battery voltage is not present, substitute a known good ECU, and retest. If voltage is now as specified, replace original ECU.
5. Reconnect "B" harness connector to main wire harness, and disconnect 2-pin connector on P/S switch. If battery voltage is present, replace P/S switch. If battery voltage is not present, repair short in Red wire from positive ECU terminal B8 to P/S switch. (Scheme 10)

Scheme 13

1. Disconnect 8-pin TDC/CRANK/CYL sensor connector. Using an ohmmeter, measure resistance between terminals B and F and between terminals C and G. (Scheme 13) If resistance readings are 350-700 ohms for each pair, go to next step. If resistance readings are not as specified, replace distributor assembly.
2. Check for continuity between each terminal and chassis ground. If continuity exists on any terminal, replace distributor assembly.

1. Connect test harness between ECU and ECU wire harness connector. (Scheme 11)
2. Turn ignition switch to ON position. Measure voltage between ECU terminals D11 (+) and D22 (-). (Scheme 10) Open and close throttle while observing voltmeter. Voltage reading should be approximately 0.5 volt with throttle in full closed position and 4.5 volts at wide open throttle. Transition from 0.5 to 4.5 volts should be smooth as throttle is opened.
3. If vehicle is equipped with a manual transmission or is not equipped with an A/T control unit, go to next step. On A/T vehicles equipped with A/T control unit, disconnect 22-pin connector from A/T control unit. Check voltage again as throttle is opened and closed. If voltage does not fluctuate as specified in step 2), go to next step. If voltage now fluctuates as specified, replace A/T control unit.
4. If voltage is not as specified, check for short or open in wire between ECU positive terminal D11 and throttle angle sensor. (Scheme 10) If wire is okay, replace throttle angle sensor. If problem still exists, see «TESTS W/CODES»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-tests-wcodes) article in the ENGINE PERFORMANCE Section.

1. Connect test harness between ECU and main harness connector. (Scheme 11) Raise vehicle front, and support with safety stands. Connect voltmeter between ECU test harness connector terminals B10 (+) and A26 (-). (Scheme 10)
2. Turn ignition switch to ON position. Slowly rotate left front wheel. Voltage should pulsate between zero and 5 volts. If voltage pulsates as specified, go to next step. If voltage does not pulsate, check for open or short in wire between ECU positive terminal B10 and speed sensor. (Scheme 10) If wire is okay, replace faulty speed sensor or ECU.
3. Substitute a known good ECU, and recheck. If condition is rectified, replace original ECU.

Scheme 14

1. If vehicle starts and continues to run, relay is okay. To test, remove main relay, located near under-dash fuse box. Using jumper wires, connect battery voltage to No. 6 terminal and ground No. 8 terminal of main relay. (Scheme 14)
2. Using an ohmmeter, check continuity between main relay terminals No. 5 and No. 7. If continuity exists, go to step 3). If continuity does not exist, replace main relay.
3. Connect battery voltage to main relay terminal No. 5 and ground terminal No. 2. Check continuity between terminals No. 1 and No. 3 of main relay. If continuity exists, go to next step. If continuity does not exist, replace main relay.
4. Connect battery voltage to main relay terminal No. 3 and ground terminal No. 8. Check continuity between terminals No. 5 and No. 7 of main relay. If no continuity exists, replace main relay. If continuity exists, main relay is okay. If fuel pump still fails to operate, test main relay harness. See «FUEL PUMP MAIN RELAY HARNESS»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) under FUEL SYSTEM.

Electronic Air Control Valve (EACV)

See IDLE CONTROL SYSTEM .

EGR Control Solenoid Valve

See EMISSION SYSTEMS & SUB-SYSTEMS .

See AIR INDUCTION SYSTEMS .

Purge Cut-Off Solenoid Valve

See EMISSION SYSTEMS & SUB-SYSTEMS .

FUEL DELIVERY

Note. For fuel system pressure testing, see BASIC TESTING article.

Fuel Injector(s)

Disconnect 2-pin connector at injector. Using an ohmmeter, measure resistance between injector terminals. Resistance reading should be as specified. See FUEL INJECTOR RESISTANCE TEST table. If resistance reading is not as specified, replace injector(s).

FUEL INJECTOR RESISTANCE TEST

Fuel Injector Resistor

Disconnect injector resistor harness connector. Check resistance between each injector resistor terminal (B, C, D and E) and power terminal (A). (Scheme 15) Resistance reading should be 5-7 ohms for each pair of terminals. If any resistance reading is not as specified, replace injector resistor.

Scheme 15

Scheme 16

1. Turn ignition off. Disconnect main relay harness connector. Check for continuity between connector terminal No. 2 and chassis ground. (Scheme 16) If continuity exists, go to next step. If continuity does not exist, repair open in Black wire from No. 2 terminal. See «WIRING DIAGRAMS»(/honda/accord/iv-1989-1993/remont/wiring-diagrams-engine-performance/#wiring-diagrams) article.
2. Using a voltmeter, measure voltage between connector terminals No. 1 (positive) and No. 2 (negative). (Scheme 16) If battery voltage exists, go to next step. If battery voltage does not exist, check wiring between battery and main relay as well as ECU fuse in underhood relay box. Repair as required.
3. Turn on ignition. Measure voltage between connector terminals No. 5 (positive) and No. 2 (negative). (Scheme 16) If battery voltage exists, go to next step. If battery voltage does not exist, check wiring from ignition switch and main relay. Check fuse No. 2 in dash fuse box and wiring from fuse box to main relay. Repair or replace as necessary.
4. Connect voltmeter to connector terminals No. 6 (positive) and No. 2 (negative). (Scheme 16) Turn ignition switch to START position. If battery voltage is present, go to next step. If specified voltage is not present, check wiring between ignition switch and main relay. Check fuse No. 1 (A/T) or fuse No. 9 (M/T). Check wiring from fuse box to main relay. Repair or replace as necessary.
5. Connect a jumper wire between connector terminals No. 5 and No. 7. (Scheme 16) Turn on ignition. Fuel pump should operate. If fuel pump fails to operate, check fuel pump wiring.

Electric Load Detector

1. Connect ECU test harness between ECU and main harness connector. (Scheme 11) Turn ignition on. Using a voltmeter, measure voltage between test harness terminals D10 (+) and A26 (-). (Scheme 10)
2. Turn headlight switch to first position. Voltmeter should read 2.5-3.5 volts. Turn headlight switch to second position. Voltmeter should read 1.5-2.5 volts. If voltage reading is not as specified, replace electric load detector.

1. With ignition off, disconnect 2-pin EACV connector. Using an ohmmeter, measure resistance between EACV terminals. If resistance reading is 8-15 ohms, go to next step. If resistance is not as specified, replace EACV.
2. Check for continuity between each EACV terminal and chassis ground. If continuity is present on any terminal, replace EACV.

Fast Idle Valve

1. Start engine. Remove fast idle valve cover. Place finger on valve seat area and ensure air flow exists with engine cold and idling. If air flow does not exist, replace fast idle valve.
2. Warm engine to full operating temperature (cooling fan comes on). Ensure valve is completely closed. Valve is leaking if suction can be felt in valve seat area. Replace valve if faulty.

IGNITION SYSTEM

Note. For basic ignition checks, see BASIC TESTING article in the ENGINE PERFORMANCE Section.

Scheme 17

Scheme 18

1. Start engine, and bring to full operating temperature. Disconnect vacuum hose from EGR valve, and connect a vacuum gauge. If vacuum does not exist, go to step 3). If vacuum is present, disconnect 4-pin connector from control box, and recheck.
2. If vacuum is no longer present, inspect for a short to ground in Pink wire between EGR control solenoid valve and ECU. (Scheme 17) If wire is okay, check for faulty ECU. If vacuum is still present, check vacuum hose routing of EGR system. If hoses are routed properly, replace EGR control solenoid valve.
3. Disconnect 4-pin harness connector at control box. Using jumper wires, connect battery voltage to terminal A of connector. (Scheme 18) While observing vacuum gauge, ground terminal B of harness connector. If within one second vacuum gauge does not read approximately 8 in. Hg, go to next step. If specified vacuum reading exists, solenoid valve is okay.
4. Turn off ignition. Check vacuum hoses to solenoid valve for improper routing, bad connections, leaks and restrictions. If hoses are okay, disconnect lower hose on EGR control solenoid valve, and connect a vacuum gauge to hose. Start engine, and allow to idle. 5) If vacuum gauge reads 6-10 in. Hg, replace EGR control solenoid valve. If specified vacuum does not register on gauge, replace CVC valve.

EGR Valve

1. Ensure all connectors between EGR valve lift sensor and ECU are securely connected. Warm engine to full operating temperature.
2. Disconnect vacuum hose from EGR valve. Connect a vacuum pump to EGR valve, and apply vacuum. EGR valve should hold vacuum and engine should die once vacuum is applied. If results are not as specified, replace EGR valve.

Scheme 19

1. Connect EGR Valve Lift Sensor Test Harness (07LAJ-PT3020A ) between EGR valve lift sensor and engine wire harness. (Scheme 19) Turn on ignition. Using a voltmeter, measure voltage between Red (positive) terminal and Green (negative) terminal.
2. If voltage reading is approximately 5 volts, go to next step. If voltage is not as specified, repair open in Yellow/White wire and/or Green/White wire between EGR valve and ECU.
3. Measure voltage between White (positive) terminal and Green (negative) terminal. If voltage reading is approximately 1.2 volts, go to next step. If voltage is not as specified, check for short in White/Black or Yellow wires between ECU and EGR valve lift sensor. If wiring is okay, replace EGR valve.
4. Disconnect vacuum hose from EGR valve, and connect vacuum pump to EGR valve. While observing voltmeter, slowly apply 8 in. Hg to EGR valve. If voltage increases smoothly from 1.2-4.0 volts as vacuum is applied to EGR valve, EGR valve lift sensor is okay. If voltage does not increase smoothly, replace EGR valve.

1. Disconnect vacuum hose from purge control diaphragm valve located on charcoal canister. Connect a vacuum gauge to hose. Start engine, and allow to idle. Engine coolant temperature must be below 167 °F (75°C).
2. If vacuum is not present, go to step 4). If vacuum is present, disconnect 4-pin harness connector at purge cut-off solenoid valve. Using a voltmeter, measure voltage between Black/Yellow (+) and Red/Green (-) wires.
3. If battery voltage exists, inspect vacuum hose for leaks, blockage and incorrect routing. If hose is okay, replace purge cut-off solenoid valve. If voltage does not exist, measure voltage between positive terminal and chassis ground. If battery voltage does not exist, repair open circuit in Black/Yellow (+) wire. If voltage exists, check for open circuit between negative terminal and ECU. If wire is okay, replace ECU.
4. Warm engine to full operating temperature (cooling fan comes on). Turn off engine, and restart. If vacuum now exists, proceed to «CHARCOAL CANISTER»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-systemcomponent-tests__charcoal-canister) . If vacuum is not present, disconnect or 4-pin harness connector at purge cut-off solenoid valve.
5. If vacuum now exists, check for short circuit in negative wire between harness connector and ECU. If wire is okay, substitute known good ECU, and retest. If system now operates properly, replace ECU. If vacuum still does not exist, check vacuum hose for leaks, blockage and improper routing. If hose is okay, replace purge cut-off solenoid valve.

Charcoal Canister

Connect vacuum gauge to canister purge air hose, located at bottom of canister. (Scheme 20) Start engine, and increase engine speed to 3500 RPM. Vacuum should register on gauge within one minute. If results are not as specified, inspect purge hose for blockage. If hose is okay, replace charcoal canister.

Scheme 20

2-Way Valve

1. Remove fuel filler cap. Remove vapor hose from fuel tank side of 2-way valve, and install "T" fitting. Connect vacuum gauge to "T" fitting and a vacuum pump to end of hose.
2. Slowly apply vacuum while watching vacuum gauge. Vacuum reading should stabilize momentarily at 0.2-0.6 in. Hg. If reading is as specified, go to next step. If vacuum stabilizes (valve opens) at less than 0.2 in Hg or greater than 0.6 in. Hg, replace 2-way valve, and retest.
3. Move vacuum hose from vacuum to pressure fitting side of vacuum pump. Slowly pressurize vapor line while watching gauge. If pressure stabilizes at 0.4-1.4 in. Hg, valve is okay. If pressure stabilizes at less than 0.4 in. Hg or greater than 1.4 in. Hg, replace 2-way valve, and retest.

POSITIVE CRANKCASE VENTILATION (PCV)

Check crankcase ventilation hoses and connections for leaks and clogging. Start engine. With engine at idle, pinch and release PCV hose. Clicking noise should be heard. If no clicking noise is heard, verify if manifold vacuum is present. If manifold vacuum is present, replace PCV valve, and recheck.

See also:
• BASIC TESTING
• TESTS W/CODES
• WIRING DIAGRAMS
• A/C-HEATER SYSTEM - MANUAL
• POWER & GROUND CIRCUITS TERMINAL IDENTIFICATION
• CHARCOAL CANISTER