Engine Controls - System/component Tests: Other Honda Prelude IV

AIR INTAKE SYSTEM

Note. DO NOT adjust by-pass valve full-close screw. Adjustment is preset at factory.

Scheme 59

1. Check valve shaft for binding and sticking. Check valve for smooth movement. Ensure tab on valve contacts stopper when valve is fully open. (Scheme 59)
2. Ensure tab of by-pass valve contacts full-close screw when valve is fully closed. If any fault is found, clean linkage and shafts using carburetor cleaner. If problem still exists after cleaning, disassemble intake manifold and inspect by-pass valve.

Scheme 60

1. Start and idle engine. Remove vacuum hose No. 13 from by-pass control diaphragm. (Scheme 60) Connect vacuum gauge to hose. If vacuum exists, go to next step. If vacuum does not exist, remove vacuum hose No. 12 from vacuum tank. Check for vacuum. If vacuum exists, go to step 3). If vacuum does not exist, repair blockage or leak between vacuum tank and intake manifold. Retest system.
2. Increase engine speed to 5000 RPM. Check for vacuum at hose No. 13. If vacuum does not exist, solenoid is okay. If vacuum exists, unplug connector at solenoid. Check for vacuum again. If vacuum still exists, replace solenoid valve. If vacuum no longer exists, solenoid valve is okay.
3. Unplug connector at solenoid. Measure voltage between Black/Yellow (positive) wire terminal and Pink (negative) wire terminal. If battery voltage exists, replace by-pass control solenoid valve. If battery voltage does not exist, check continuity of harness wiring to solenoid valve.

Intake Control Diaphragm (H22A1 & H23A1 Engines)

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

Intake Control Solenoid Valve (H22A1 & H23A1 Engines)

1. Start and idle engine. Remove upper vacuum hose from intake control solenoid valve, located at top of engine, on left side. Connect vacuum gauge to solenoid valve. If vacuum does not exist, go to next step. If vacuum exists, increase engine speed to 4600 RPM (H22A1 engine) or 4800 RPM (H23A1 engine). If vacuum still exists, go to step 4). If vacuum no longer exists, solenoid valve is okay.
2. Disconnect lower vacuum hose of solenoid valve from air chamber. Connect vacuum gauge. If vacuum exists, go to next step. If vacuum does not exist, inspect vacuum line for improper connection, cracks and blockage in hose. If vacuum line is okay, clean manifold port.
3. Unplug connector from intake control solenoid valve. Measure voltage between Black/Yellow and Pink wire terminals. If battery voltage does not exist, solenoid valve is okay. If battery voltage exists, replace intake control solenoid valve.
4. Unplug connector from solenoid valve. If vacuum no longer exists, solenoid valve is okay. If vacuum still exists, replace solenoid valve.

Ground Circuits

1. Measure resistance to ground at appropriate ECM ground terminals. See «POWER & GROUND CIRCUIT TERMINAL IDENTIFICATION»(ref-15830-S17663481862001010800000) table. (Scheme 61) Resistance should be zero ohms for each circuit. If resistance is not zero ohms, repair open to ground.
2. Connect negative lead of DVOM to a good ground. Connect positive lead to each ground terminal. With engine running, voltmeter should indicate less than 0.1 volt. If voltage is greater than 0.1 volt, check for open, corrosion, or loose connection on ground lead.

Scheme 61

1. Check for battery voltage between ECM power terminal and ground. See «POWER & GROUND CIRCUIT TERMINAL IDENTIFICATION»(ref-15830-S17663481862001010800000) table. (Scheme 61) If battery voltage does not exist, check appropriate ECM fuse in underhood fuse box. See «ECM POWER CIRCUIT FUSE IDENTIFICATION»(ref-15830-S14723871042001010800000) table. If fuse is okay, check for an open in wire between underhood fuse box and appropriate ECM power circuit terminal.
2. Turn ignition on. Check for battery voltage between appropriate ECM power circuit terminal and ground. See «POWER & GROUND CIRCUIT TERMINAL IDENTIFICATION»(ref-15830-S17663481862001010800000) table. If battery voltage does not exist, check appropriate fuse in underhood fuse box. See «ECM POWER CIRCUIT FUSE IDENTIFICATION»(ref-15830-S14723871042001010800000) table. If fuse is okay, check for open in wire between fuse box and appropriate ECM power circuit terminal, and check for defective ignition switch. POWER & GROUND CIRCUIT TERMINAL IDENTIFICATION Application (1) ECM Terminal Ground Circuits A23, A24, A26 & B2 Power Circuits Ignition Switch In OFF Position D1 Ignition Switch In ON Position A25 & B1 (1) For terminal location (Scheme 61) ECM POWER CIRCUIT FUSE IDENTIFICATION Application Fuse Prelude Ignition Switch In OFF Position CLOCK Ignition Switch In ON Position BACK-UP

ENGINE SENSORS & SWITCHES

Note. Test Harness (07LAJ-PT3010A ) is required for testing certain components or systems. (Scheme 62) Connect test harness between control unit and main wiring harness connectors.

Scheme 62

BAROMETRIC PRESSURE (BARO) SENSOR

Barometric pressure (BARO) sensor is built into ECM. See TESTS W/CODES article in this section for testing.

EGR VALVE LIFT SENSOR

See EMISSION SYSTEMS & SUB-SYSTEMS .

HEATED OXYGEN SENSOR (HO2S)

Note. Heated oxygen sensor may also be referred as O2 sensor. See OXYGEN SENSOR (O2S) .

1. Unplug 4-pin connector at HO2S. Sensor is threaded into exhaust manifold or exhaust pipe. Turn ignition on. Measure voltage between White and Green/White wires at HO2S connector. If voltage is less than .1 volt, go to next step. If voltage is greater than .1 volt, replace HO2S.
2. Check for open in White wire between ECM connector terminal D14 and HO2S. Check Green/White wire of ECM connector terminal D22. Repair wire(s) as necessary. Recheck system.

OXYGEN SENSOR (O2S)

Note. All models except Civic D15B8 use heated oxygen sensor. See HEATED OXYGEN SENSOR (HO2S) . Oxygen sensor may be referred to as O2 sensor.

POWER STEERING PRESSURE (PSP) SWITCH

1. Connect test harness between ECM and wiring harness. (Scheme 62) Turn ignition on. Measure voltage between test harness terminals B8 and A26. (Scheme 61) If voltage is greater than one volt, proceed to the next step. If voltage is not greater than one volt, go to step 4).
2. Unplug connector on PSP switch. Switch is located on steering gear. On Accord, connect jumper wire between Green and Black wire terminals. Connect jumper wire between Red/Green and Black wire terminals.
3. Check for voltage at test harness terminals A26 and B8. If voltage does not exist, replace PSP switch. If voltage exists, repair open in Red/Green wire between ECM terminal B8 and PSP switch, or Black wire between PSP switch and ground.
4. Start engine. Turn steering wheel slowly. Measure voltage between test harness terminals A26 and B8. If battery voltage exists, PSP signal is okay. If battery voltage does not exist, go to next step.
5. Turn ignition off. Unplug test harness connector "B" from main wiring harness only, not ECM. Turn ignition on. If battery voltage exists, go to next step. If battery voltage does not exist, replace ECM and retest system.
6. Reconnect harness connector "B" to main wiring harness. Unplug connector from PSP switch. If battery voltage exists, replace PSP switch. If battery voltage does not exist, repair short in Green, Brown/Red or Red/Green wire between ECM terminal B8 and PSP switch.

Scheme 63

1. Unplug TDC/CKP/CYP sensor connector, located at distributor. Measure resistance between terminals "B" and "F". Measure resistance between terminals "C" and "G". (Scheme 63) Measure resistance between terminals "D" and "H". If resistance is 350-700 ohms for each pair, go to next step. If any measurement is not as specified, replace distributor.
2. Check for continuity between each terminal and chassis ground. If continuity exists at any terminal, replace distributor.

THROTTLE POSITION (TP) SENSOR

1. Turn ignition off. Connect test harness between ECM and vehicle harness connector. (Scheme 62)
2. Turn ignition on. Measure voltage between test harness terminals D11 and D22. Open and close throttle while observing voltmeter. Voltage should be about 0.5 volt with throttle fully closed and 4.5 volts with throttle wide open. Voltage should change smoothly as throttle opens and closes.
3. If voltage is not as specified on Prelude M/T, replace TP sensor. If voltage is as specified, replace ECM and retest system. If voltage is not as specified on Prelude A/T, go to next step.
4. Unplug 22-pin connector from Transmission Control Module (TCM). TCM is located below center of dashboard. Measure voltage again as throttle is opened and closed. If voltage does not change as specified in step 2), go to next step. If voltage now changes as specified, replace TCM.
5. If voltage is not as specified, check for short or open in Red/Black wire between ECM terminal D11 and TP sensor. If wire is okay, replace TP sensor. If problem still exists, see «TESTS W/CODES»(ref-15805) article in the ENGINE.PERFORMANCE Section

VEHICLE SPEED SENSOR (VSS)

1. Turn ignition off. Connect test harness between ECM and main harness connector. (Scheme 62) Raise and support front of vehicle so front wheels are free to rotate. Connect voltmeter between ECM terminals B10 and A26. (Scheme 61)
2. Turn ignition on. Slowly rotate left front wheel. Voltage should pulse between zero and specified voltage. See «VEHICLE SPEED SENSOR (VSS) TEST»(ref-15830-S28466128112001010800000) table. If voltage pulses as specified, replace ECM and retest system. If voltage does not pulse as specified, check for open or short in wiring between ECM terminal B10 and speed sensor. See «WIRING DIAGRAMS»(ref-15821) article in this section. If wiring is okay, replace defective VSS or ECM.

VEHICLE SPEED SENSOR (VSS) TEST

Scheme 64

1. If vehicle starts and continues to run, relay is okay. To test, remove main relay, located under left side of dash. Using jumper wires, connect terminal No. 6 to battery voltage. Connect terminal No. 8 to ground. (Scheme 64)
2. Check for continuity between relay terminals No. 5 and 7. Continuity should exist. If continuity does not exist, replace relay. Disconnect battery leads. Repeat measurement. If continuity does not exist, go to next step. If continuity exists, replace relay.
3. Connect battery voltage to relay terminal No. 5. Connect terminal No. 2 to ground. Check for continuity between terminals No. 1 and 3. Continuity should exist. Disconnect battery leads. Repeat measurement. Continuity should not exist. If continuity exists, replace relay.
4. Connect battery voltage to relay terminal No. 3. Connect terminal No. 8 to ground. Check for continuity between terminals No. 5 and 7. Disconnect battery leads. Repeat measurement. If continuity does not exist, relay is okay. If continuity exists, replace relay. If fuel pump still fails to operate, test main relay harness. See MAIN RELAY HARNESS under «FUEL CONTROL»(ref-15830-S34359803012001010800000) under FUEL SYSTEM.

IAB Control Solenoid (2.3L)

See AIR INDUCTION SYSTEMS .

Idle Air Control (IAC) Valve

See IDLE CONTROL SYSTEM .

EGR Control Solenoid Valve

See EXHAUST GAS RECIRCULATION (EGR) SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS.

Intake Air Control Solenoid Valve

See AIR INDUCTION SYSTEMS .

EVAP Purge Control Solenoid Valve

See FUEL EVAPORATION under EMISSION SYSTEMS & SUB-SYSTEMS.

FUEL DELIVERY

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

Fuel Injectors

Unplug connector at injector. Measure resistance between injector terminals. Resistance should be as specified. Refer to the FUEL INJECTOR RESISTANCE table. If resistance is not as specified, replace injector.

INJECTOR RESISTANCE

FUEL INJECTOR RESISTANCE

Fuel Injector Resistor

Unplug injector resistor harness connector. Injector resistor is located over at upper left firewall. Measure resistance between each injector resistor terminal ("B", "C", "D" and "E") and power terminal ("A"). (Scheme 65) Resistance should be 5-7 ohms for each pair of terminals. If any measurement is not as specified, replace injector resistor.

Scheme 65

Scheme 66

1. Turn ignition off. Unplug main relay harness connector. Check for continuity between connector terminal No. 2 and chassis ground. (Scheme 66) If continuity exists, go to next step. If continuity does not exist, repair open in Black wire from terminal No. 2 to ground. See «WIRING DIAGRAMS»(ref-15821) article in this section.
2. Measure voltage between connector terminal No. 1 and body ground. If battery voltage exists, go to next step. If battery voltage does not exist, check wiring between battery and main relay, and check ECM fuse in underhood relay box. Repair as necessary.
3. Turn ignition on. Measure voltage between relay connector terminal No. 5 and body ground. 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. 23. Check wiring from fuse box to main relay. Repair or replace as necessary.
4. Connect voltmeter to connector terminal No. 6 and body ground. Turn ignition switch to START position. If battery voltage exists, go to next step. If battery voltage does not exist, check wiring between ignition switch and main relay. Check wiring from fuse box to main relay. Repair or replace fuse or wiring as necessary.
5. Connect jumper between connector terminals No. 5 and 7. Turn ignition on. Fuel pump should operate. If fuel pump fails to operate, check fuel pump wiring.

Electric Load Detector

1. Unplug 3-pin ELD connector (located on right fender apron near underhood fuse panel). Turn ignition on. Measure voltage between Black/Yellow wire (+) and Black wire (-) at ELD connector. If battery voltage exists, go to step 3). If battery voltage does not exist, go to next step.
2. Measure voltage between Black/Yellow wire and chassis ground. If battery voltage exists, repair open in Black wire between ELD connector and ground connection behind right kick panel. If battery voltage does not exist, repair open in Black/Yellow wire between ELD connector and No. ECM fuse in underhood fuse panel.
3. Measure voltage in Green/Red wire between ELD connector and ground. If voltage is about 5 volts, go to next step. If voltage is not as specified, check for open or short in Green/Red wire between ECM and ELD connector. Repair wire as necessary.
4. Turn ignition off. Reconnect ELD connector. Connect test harness between ECM and connectors. (Scheme 62) Start engine and allow it to idle. While measuring voltage between terminals A26 and D10 of ECM connector, turn headlights on low beam. If voltage does not drop when headlights are turned on, replace ELD. If voltage drops, replace ECM with known-good unit. If voltage drop symptom disappears, replace original ECM.

1. Turn ignition off. Unplug IAC valve connector. IAC is located near throttle body. Turn ignition on. Measure voltage between Yellow/Black wire on harness connector and ground. If battery voltage exists, go to next step. If battery voltage does not exist, repair Yellow/Black wire between IAC valve and PGM-FI main relay.
2. Turn ignition off. Connect test harness to vehicle wiring harness, not to ECM. (Scheme 62) Turn ignition on. Momentarily connect terminal A9 to terminal A26. If IAC valve clicks, substitute known-good ECM and retest system. If IAC valve does not click, repair Black/Blue wire between IAC and ECM terminal A9.

Fast Idle Thermo Valve

1. Start engine. Remove fast idle valve cover. Fast idle valve is located near throttle body. Place finger on valve seat area. Check for airflow with engine cold and idling. If airflow does not exist, replace fast idle valve.
2. Warm engine to full operating temperature (cooling fan comes on). Verify valve is completely closed. Valve is leaking if engine speed decreases when lower port is covered and suction can be felt in valve seat area. Replace valve if valve operation is not as specified.

IGNITION SYSTEM

Note. For basic ignition checks, see BASIC TESTING article in this section.

EGR Valve

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

1. Start and idle engine. Disconnect hose No. 16 from EGR valve, located at top of engine. Connect vacuum pump/gauge to hose. If vacuum exists, go to next step. If vacuum does not exist, go to step 4).
2. Unplug 2-pin connector from EGR control solenoid valve, located over left front fenderwell. Check for vacuum on hose No. 16. If vacuum does not exist, go to next step. If vacuum exists, check EGR system vacuum hose routing. If hoses are okay, replace EGR control solenoid valve.
3. Turn ignition off. Unplug connector "A" from ECM. Check for continuity between ground and Red wire at 2-pin connector. If continuity exists, repair short in appropriate wire. If continuity does not exist, replace ECM and retest system.
4. Connect vacuum pump/gauge to EGR valve. With engine idling, apply 8 in. Hg vacuum to EGR valve. If engine stalls or runs roughly, and EGR valve holds vacuum, go to next step. If engine operation remains same or EGR valve does not hold vacuum, replace EGR valve.
5. Turn ignition off. Unplug 2-pin connector from EGR control solenoid valve, located over left front fenderwell. Turn ignition on. Measure voltage between harness connector Black/Yellow wire and ground. If battery voltage exists, go to next step. If battery voltage does not exist, repair Black/Yellow wire between harness connector and fuse panel.
6. Connect vacuum pump/gauge to hose disconnected in step 1). Connect fused jumper wire between positive battery terminal and Red wire on EGR solenoid valve connector. Observe voltmeter while connecting jumper wire between Black/Yellow wire on EGR solenoid valve connector and negative battery terminal.
7. Gauge should indicate about 8 in. Hg within one second. If gauge indicates as specified, go to next step. If gauge does not indicate as specified, go to step 13).
8. Turn ignition off. Reconnect vehicle harness. Unplug 3-pin connector from EGR valve lift sensor, located on EGR valve. Turn ignition on. Measure voltage between Red/White and Green/White wires on harness connector. If voltage is about 5 volts, go to step 9). If voltage is not about 5 volts, go to step 15).
9. Turn ignition off. Reconnect wiring to valve lift sensor. Connect test harness. (Scheme 62) Turn ignition on. Measure voltage between terminals D12 and D22 with no vacuum applied to EGR valve. Apply 8 in. Hg vacuum to EGR valve. Voltage should be about 1.2 volts with no vacuum applied and 4.3 volts with vacuum applied. If voltage is not as specified, go to next step. If voltage is as specified, go to step 11).
10. Check for open or short circuit in White/Black wire between EGR valve and ECM terminal D12. (Scheme 61) If wire is okay, replace EGR valve.
11. Observe voltmeter as vacuum is applied and released. If voltage increases and decreases smoothly, go to next step. If voltage does not change smoothly, replace EGR valve.
12. Reconnect hose to EGR valve. Start and idle engine. Connect jumper wire between terminals A11 and A26. If engine stalls or runs roughly, replace ECM and retest system. If engine does not stall or run rough, repair open in Red wire between ECM terminal A11 and EGR control solenoid valve.
13. Turn ignition off. Inspect hoses No. 16 and 24 for leaks, restrictions and misrouting. If hoses are okay, go to next step. Make any repairs as necessary.
14. Disconnect lower hose from EGR control solenoid. Connect vacuum pump/gauge to hose. Start and idle engine. If 6-10 in. Hg vacuum exists, replace EGR solenoid valve. If vacuum is not 6-10 in. Hg, replace EGR valve.
15. Measure voltage at Red/White wire. If voltage is not about 5 volts, go to next step. If voltage is about 5 volts, repair open in wire between EGR valve and ECM terminal D22.
16. Turn ignition off. Connect test harness connector "D" to ECM only, not to vehicle harness. Turn ignition on. Measure voltage between terminals D20 and D22. If voltage is about 5 volts, repair open in Red/White wire between EGR lift sensor and ECM terminal D20. If voltage is not about 5 volts, replace ECM and retest system.

D15Z1

1. Start and idle engine. Disconnect vacuum hose from EGR valve, located to rear of distributor. Connect vacuum pump/gauge to hose. If vacuum exists, go to next step. If vacuum does not exist, go to step 4).
2. Unplug 2-pin connector from control box. Control box is located at top center of firewall. If vacuum no longer exists, go to next step. If vacuum still exists, check EGR system vacuum hose routing.
3. Turn ignition off. Unplug connector "A" from ECM. Check for short in Pink/Green wire (Orange/Blue wire after connector) between EGR control solenoid valve and ECM terminal A11. If wire is okay, replace ECM and retest system.
4. Connect vacuum pump/gauge to EGR valve. Apply 8 in. Hg vacuum to EGR valve. If engine stalls or runs roughly, and EGR valve holds vacuum, go to next step. If engine operation remains same, or EGR valve does not hold vacuum, replace EGR valve.
5. Turn ignition off. Unplug 2-pin connector from control box, located at top center of firewall. Turn ignition on. Measure voltage between harness connector Black/Yellow wire and ground. If battery voltage exists, go to next step. If battery voltage does not exist, repair Black/Yellow wire between EGR control solenoid valve and fuse panel. EGR control solenoid valve is located in control box.
6. Reconnect vacuum pump/gauge to hose. Start and idle engine. Connect fused jumper wire between terminal "A" (Black/Yellow wire on mating harness connector) of control box connector and positive battery terminal.
7. Observe vacuum gauge while connecting remaining control box terminal to ground. If gauge indicates about 8 in. Hg within one second, go to next step. If gauge indication is not as specified, go to step 13).
8. Turn ignition off. Reconnect vehicle harness to control box. Unplug 3-pin connector from EGR valve. EGR valve is located behind distributor. Turn ignition on. Measure voltage between Yellow/White and Green/White wires at harness connector. If voltage is about 5 volts, go to next step. If voltage is not about 5 volts, go to step 15).
9. Turn ignition off. Reconnect vehicle harness to EGR valve. Connect test harness. (Scheme 62) Turn ignition on. Measure voltage between terminals D12 and D22 with no vacuum applied to EGR valve. Apply 8 in. Hg vacuum to EGR valve. Voltage should be about 1.2 volts with no vacuum applied and 4.3 volts with vacuum applied. If voltage is as specified, go to step 11).
10. If voltage is not as specified, check for open or short circuit in White/Black wire between EGR valve and ECM terminal D12. If wire is okay, replace EGR valve.
11. Observe voltmeter as vacuum is applied and released. If voltage increases and decreases smoothly, go to next step. If voltage change is not as specified, replace EGR valve.
12. Reconnect hose to EGR valve. Start and idle engine. Connect jumper wire between terminals A11 and A26. If engine stalls or runs roughly, replace ECM and retest system. If engine does not stall or run roughly, repair open in Pink/Green or Orange/Blue wire between ECM terminal A11 and EGR control solenoid valve.
13. Turn ignition off. Check vacuum hoses for leaks, restrictions and misrouting. If hoses are okay, go to next step. Repair as necessary.
14. Disconnect lower hose from EGR control solenoid valve. EGR control solenoid valve is located in control box, at top center of firewall. Connect vacuum gauge/pump to hose. Start and idle engine. If gauge indicates 6-10 in. Hg vacuum, replace EGR control solenoid valve. If vacuum is not as specified, replace EGR vacuum control valve, located in control box.
15. Measure voltage between Yellow/White wire and body ground. If voltage is not about 5 volts, go to next step. If voltage is about 5 volts, repair open in Green/White wire between ECM terminal D22 and EGR valve.
16. Turn ignition off. Connect test harness. (Scheme 62) Turn ignition on. Measure voltage between terminals D20 and D22. If voltage is about 5 volts, repair open in Yellow/White wire between EGR valve and ECM terminal D20. If voltage is not about 5 volts, replace ECM and retest system.

1. Disconnect vacuum hose from EVAP purge control diaphragm valve, located on charcoal canister. Connect vacuum gauge to hose. Start and idle engine. Engine coolant temperature must be less than 167°F (75°C).
2. If vacuum does not exist, go to step 4). If vacuum exists, unplug connector at EVAP purge control solenoid valve. Refer to the «EVAP PURGE CONTROL SOLENOID LOCATION»(ref-15830-S16397973142001010800000) table. Measure voltage between specified wires. See «EVAP PURGE CONTROL SOLENOID CONNECTOR IDENTIFICATION»(ref-15830-S36675227772001010800000) table. EVAP PURGE CONTROL SOLENOID LOCATION Application Location Prelude Near Throttle Position Sensor EVAP PURGE CONTROL SOLENOID CONNECTOR IDENTIFICATION Application Positive Terminal Negative Terminal Prelude Black/Yellow Red/Green
3. If battery voltage exists, inspect vacuum hose for leaks, blockage and incorrect routing. If hose is okay, replace EVAP purge control 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 appropriate positive wire. If voltage exists, check for open circuit between negative terminal and ECM. If wire is okay, replace ECM.
4. Warm engine to full operating temperature (cooling fan comes on). Turn off and restart engine. If vacuum now exists, go to «EVAP CANISTER»(ref-15830-S20436383842001010800000) . If vacuum does not exist, unplug connector at EVAP purge control solenoid valve.
5. If vacuum now exists, check for short circuit in negative wire between harness connector and ECM. If wire is okay, substitute known good ECM. Retest system. If system now operates properly, replace ECM. If vacuum still does not exist, check vacuum hose for leaks, blockage and improper routing. If hose is okay, replace EVAP purge control solenoid valve. NOTE: EVAP canister may also be referred to as charcoal canister or EVAP charcoal canister.

EVAP Canister

Connect vacuum gauge to canister purge air hose, located at bottom of canister. (Scheme 67) Start engine. 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 67

EVAP 2-Way Valve

1. Remove fuel filler cap. Disconnect vapor hose from fuel tank side of 2-way valve, located in fuel tank area. Install "T" fitting into hose. Connect vacuum gauge and vacuum pump to "T" fitting.
2. Slowly apply vacuum while observing vacuum gauge. Vacuum should stabilize momentarily at 0.2-0.6 in. Hg. If vacuum is as specified, go to next step. If vacuum is not as specified, replace 2-way valve. Retest system.
3. Move vacuum hose from vacuum to pressure fitting side of vacuum pump. Slowly pressurize vapor line while observing 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 valve and retest.

POSITIVE CRANKCASE VENTILATION (PCV)

Inspect crankcase ventilation hoses and connections for leaks and clogging. Start engine. With engine at idle, pinch and release PCV hose. Valve should click. If valve does not click, check for vacuum at PCV valve end of hose. If manifold vacuum exists, replace PCV valve and recheck. If vacuum does not exist, clear blockage in hose.