Engine Controls - System/component Tests Nissan Pathfinder I

INTRODUCTION

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

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

POWER VALVE CONTROL SOLENOID

Remove vacuum lines and electrical connector from solenoid. Remove solenoid from vehicle. Connect hand-held vacuum pump to middle vacuum port of solenoid. Apply battery voltage to solenoid. Ensure correct polarity is used or damage to solenoid may result. Apply vacuum. As battery voltage is applied and removed from solenoid, vacuum should alternately bleed from remaining 2 ports.

SURGE TANK & ONE-WAY CHECK VALVE

Apply vacuum to surge tank located on firewall. Vacuum should hold. Apply vacuum to both sides of one-way check valve. Valves should hold vacuum in only one direction. Ensure valve is installed with holding side away from vacuum source.

SWIRL CONTROL VALVE

The Pickup swirl control valve actuator and solenoid are located on right side of engine, behind throttle body. Also see appropriate SWIRL CONTROL VALVE diagnostic chart.

Valve should close when vacuum is applied to swirl control valve actuator and should open when vacuum is not applied.

SWIRL CONTROL VALVE SOLENOID

Remove vacuum lines and electrical connector from solenoid. Remove solenoid from vehicle. Connect hand-held vacuum pump to middle vacuum port of solenoid. Apply battery voltage to solenoid. Ensure correct polarity is used or damage to solenoid may result. Apply vacuum. As battery voltage is applied and removed from solenoid, vacuum should alternately bleed from remaining 2 ports.

ELECTRONIC CONTROL UNIT (ECU) POWER & GROUND SIGNALS

See appropriate ECU POWER SOURCE & GROUND diagnostic chart.

ENGINE SENSORS & SWITCHES

Note. For location and identification of ECU terminals, refer to the appropriate WIRING DIAGRAMS article.

AIRFLOW METER

Ensure there is no dust or foreign material in hot wire air passage. Faults in the airflow meter circuit should set a trouble code. If Code 12 is set, go to CODE 12 diagnostic procedures in TESTS W/CODES article. Also see AIRFLOW METER VOLTAGE TEST table.

AIRFLOW METER VOLTAGE TEST (1)

AIR CONDITIONER SWITCH

Check switch signal voltage at appropriate ECU terminal. With engine running both and A/C and blower switches on, voltage should be zero volt. With engine running and A/C off switch, voltage should be 11-14 volts.

AIR TEMPERATURE SENSOR (PICKUP 2.4L)

On Pickup, the air temperature sensor is on air cleaner box, near idle switch. Measure sensor resistance across sensor terminals. At 68°F (20°C), resistance should be about 2100-2900 ohms. At 176°F (80°C), resistance should be about 270-380 ohms. Check sensor voltage values against values in AIR TEMPERATURE SENSOR VOLTAGE TEST table. Replace sensor if voltages are not within specifications.

AIR TEMPERATURE SENSOR VOLTAGE TEST (1)

CRANKSHAFT ANGLE SENSOR

Crankshaft angle sensor is part of the distributor. If a fault is present in crank angle sensor, Code 11 may be set in ECU memory. If Code 11 is set, go to CODE 11 diagnostic procedures in TESTS W/CODES article.

To test crank angle sensor, leave sensor wiring connected. Using a logic probe or DVOM with an analog bar graph function, connect negative lead to ground and alternately connect positive lead to one-degree signal and 120/180-degree signal terminals of ECU. Refer to the CRANK ANGLE SENSOR ECU INPUT SIGNAL TERMINALS table.

With the engine cranking, peak voltage for one-degree signal should measure about 2.3-2.8 volts on DVOM. Peak voltage for 120/180-degree signal should measure about .1-.4 volt with engine cranking. If either signal is not present, check harness for short or open circuit. If no problems are found, replace crank angle sensor.

Note. It is possible to measure crank angle sensor voltage with a conventional DVOM without bar graph function; however, it may not be easy to determine peak voltage signal due to the averaging of signal.

CRANK ANGLE SENSOR ECU INPUT SIGNAL TERMINALS (1)

DETONATION (KNOCK) SENSOR (PATHFINDER, PICKUP 3.0L)

On Pathfinder & Pickup the detonation (knock) sensor is located on rear right side of engine block (between cylinder heads). Disconnect sensor connector. Check continuity between sensor terminal and ground. Ensure continuity exists.

ENGINE (COOLANT) TEMPERATURE SENSOR

Disconnect engine (coolant) temperature sensor connector. Measure resistance across sensor terminals. Check sensor resistance values against values in ENGINE (COOLANT) TEMPERATURE SENSOR RESISTANCE TEST table. Replace sensor if values are not as specified.

ENGINE (COOLANT) TEMPERATURE SENSOR RESISTANCE TEST (1)

EXHAUST GAS (OXYGEN) SENSOR

If fault is present in oxygen sensor circuit, Code 33 will be set in ECU memory. If Code 33 is set, go to CODE 33 diagnostic procedures in TESTS W/CODES article. Check sensor voltage values against values in the EXHAUST GAS (OXYGEN) SENSOR VOLTAGE TEST table. Replace sensor if values are not as specified.

EXHAUST GAS (OXYGEN) SENSOR VOLTAGE TEST (1)

EXHAUST GAS TEMPERATURE SENSOR (CALIFORNIA MODELS ONLY)

Place exhaust gas temperature sensor in boiling water at 212°F (100°C). Resistance at 212°F (100°C) should be 76,770-93,830 ohms. As temperature increases, sensor resistance should decrease. Check sensor voltage values against values in EXHAUST GAS TEMPERATURE SENSOR VOLTAGE TEST table. Replace sensor if values are not as specified.

EXHAUST GAS TEMPERATURE SENSOR VOLTAGE TEST (1)

NEUTRAL/INHIBITOR SWITCH

On Pathfinder and Pickup, place transmission in Neutral and check continuity between terminals of neutral/inhibitor switch. Ensure continuity exists between terminals. Continuity should not exist with transmission in any other position.

Check sensor voltage values against values in the NEUTRAL/INHIBITOR SWITCH TEST table. Replace sensor if values are not as specified. Also see appropriate NEUTRAL/INHIBITOR SWITCH, NEUTRAL SWITCH & A/T CONTROL or NEUTRAL/INHIBITOR SWITCH & RELAY diagnostic chart.

NEUTRAL/INHIBITOR SWITCH TEST (1)

POWER STEERING OIL PRESSURE SWITCH

Switch is attached to power steering high pressure hose. Signal is used by ECU to help control idle speed. Check voltage at appropriate ECU terminal with engine idling and steering wheel in straight ahead position. See appropriate PIN VOLTAGE CHART S and WIRING DIAGRAMS articles to identify proper ECU terminal for testing. Voltage should be 4.8-4.9 volts. Turn steering wheel from side to side. While steering wheel is being turned, voltage should be 0-2 volts. See appropriate POWER STEERING OIL PRESSURE SWITCH diagnostic chart.

THROTTLE POSITION SENSOR (TPS) & IDLE SWITCH

Throttle position sensor and idle switch are a combined assembly located on side of throttle body. See ADJUSTMENTS article for adjustment procedures. Check sensor voltage values against values in THROTTLE POSITION SENSOR VOLTAGE TEST table. Replace sensor if values are not as specified in table.

THROTTLE POSITION SENSOR VOLTAGE TEST (1)

VEHICLE SPEED SENSOR

On Pathfinder, Pickup, remove instrument cluster to gain access to vehicle speed sensor. Slowly turn speedometer and check continuity of vehicle speed sensor circuit. Ensure continuity exists twice per turn. (Scheme 26) Also see appropriate ECU PIN VOLTAGE CHARTS in PIN VOLTAGE CHART S article.

Scheme 26

VEHICLE SPEED SENSOR TEST (1)

RELAYS

A variety of relays are used and can be tested 2 different ways. The following relays can be tested using a ohmmeter and remotely supplied power and ground circuits

1. Fuel pump relay
2. Main relay
3. Radiator (cooling) fan relay
4. Mixture heater relay
5. Neutral/park relay.

Safety relays can be tested using an ohmmeter, voltmeter and remotely supplied power and ground circuits. All testing procedures require proper identification of relay internals. See appropriate WIRING DIAGRAMS article.

Note. The following examples are typical. For wiring colors, see WIRING DIAGRAMS article

Except Safety Relay

Turn ignition on. Ensure power to relay exists. Turn ignition off. Disconnect connector from relay being tested. Using ohmmeter, check for relay winding continuity across appropriate relay terminals. See appropriate WIRING DIAGRAMS article to identify proper relay terminals (wire colors) for testing. Energize relay and check continuity of relay output circuit.

EXAMPLE: Typical Fuel Pump Relay

1. Turn ignition on. Ensure battery voltage exists at Blue wires of safety relay and fuel pump relay. (Scheme 27) If battery voltage is not present at both Blue wires, check for a blown 10-amp power fuse or an open circuit between fuse and relays.
2. Turn ignition off. Unplug fuel pump relay. Check for continuity across Blue wire and Blue/White wire terminals. If continuity does not exist, relay is defective. If continuity exists, connect ohmmeter leads across Orange wire and Black wire terminals. Energize relay by applying battery voltage to Blue wire terminal and ground to Blue/White wire terminal. Ensure continuity exists while relay is energized.

Safety Relay

Turn ignition on and ensure power to relay exists. Turn ignition off. Disconnect safety relay connector. Using an ohmmeter, check one-way internal diode in safety relay by checking for continuity in both directions. Energize relay and check for voltage signal on relay output circuit.

EXAMPLE: Typical Safety Relay

1. Turn ignition on. Using a voltmeter, check for battery voltage at Blue wire of safety relay. (Scheme 27) If voltage is not present, check for blown 10-amp fuse or open circuit between fuse and relay.
2. Turn ignition off. Disconnect safety relay connector. Using ohmmeter, check for continuity across relay's Black wire and Blue wire terminals. Reverse ohmmeter leads. Continuity should only exist in one direction. Connect voltmeter positive lead to Red/Blue wire terminal. Connect negative voltmeter lead to Black wire terminal. Apply battery voltage to Blue wire terminal and ground to Black wire terminal. Voltmeter should show battery voltage while relay is energized.

Scheme 27

Air Injection Control Valve Solenoid

See AIR INJECTION under EMISSION SYSTEMS & SUB-SYSTEMS.

EGR/Canister Control Solenoid

See EXHAUST GAS RECIRCULATION (EGR) in this article.

Fast Idle Control Device (FICD) Solenoid (Pickup 2.4L)

On Pickup 2.4L, apply battery voltage to solenoid terminals. Solenoid should operate. Also check solenoid plunger for sticking and check for broken spring. Also see appropriate FAST IDLE CONTROL DEVICE (FICD) diagnostic chart.

Fuel Pressure Regulator Solenoid

See appropriate FUEL PRESSURE REGULATOR SOLENOID diagnostic chart. Also see FUEL DELIVERY SYSTEM under FUEL SYSTEM in this article.

See POWER VALVE CONTROL SOLENOID under AIR INDUCTION SYSTEM in this article.

See SWIRL CONTROL VALVE SYSTEM in this article. Also see appropriate SWIRL CONTROL VALVE diagnostic chart.

FUEL PRESSURE

For fuel pressure procedures and specifications, see FUEL PRESSURE under FUEL SYSTEM in BASIC TESTING article.

FUEL PRESSURE REGULATOR

Relieve fuel pressure from system. Connect fuel pressure gauge between fuel filter and fuel tube. Remove hose from fuel pressure regulator and plug intake manifold. Connect hand-held vacuum pump to pressure regulator. Turn engine on and gradually apply vacuum to regulator. Fuel pressure should decrease as vacuum increases. Compare fuel pressures to regulated pressure values listed in FUEL PRESSURE table in BASIC TESTING article. If pressures are not as specified, replace fuel pressure regulator.

See appropriate FUEL PRESSURE REGULATOR SOLENOID diagnostic chart. Remove vacuum lines and electrical connector from solenoid. Remove solenoid from vehicle. Connect hand-held vacuum pump to middle vacuum port of solenoid. Apply battery voltage to solenoid. Ensure correct polarity is used or damage to solenoid may result. Apply vacuum. As battery voltage is applied and removed from solenoid, vacuum should alternately bleed from remaining 2 ports. Solenoid resistance should be 30-40 ohms.

FUEL PUMP

If fuel pump does not run, disconnect fuel pump connector. Provide ground and battery voltage to fuel pump connector terminals. See appropriate WIRING DIAGRAMS article to identify fuel pump connector terminals (wire colors). If pump runs, see RELAYS under RELAYS & SOLENOIDS for testing, or repair open or short in harness between relay and pump. If pump does not run, replace fuel pump. Also see appropriate FUEL PUMP diagnostic chart.

FUEL PUMP RELAY

See RELAYS under RELAYS & SOLENOIDS .

START SIGNAL

Start (ON-OFF switch) signal is used for ECU control of fuel pump and pressure regulator control solenoid. See appropriate START SIGNAL diagnostic chart. Use DIAGNOSTIC CHARTS DIRECTORY table at beginning of this article to locate chart.

FEEDBACK SYSTEM (EXCEPT STANZA & 300ZX)

1. Start engine and warm to operating temperature. Ensure idle speed and timing are adjusted to specification. Monitor Green LED on ECU while increasing engine speed to about 2000 RPM for 2 minutes under no-load condition.
2. Note the number of flashes by Green LED every 10 seconds. See «ECU GREEN LED FEEDBACK RESPONSE»(/nissan/pathfinder/i-1985-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. Number of flashes during a 10-second period should at least equal number of flashes listed in table.
3. Race engine 2 or 3 times and allow to idle. Enter self-diagnostic Mode II. Disconnect throttle sensor/switch harness connector. Monitor Red LED and Green LED while idling. Red LED and Green LED should flash simultaneously. If not, adjust airflow meter (if adjustable). See ADJUSTMENTS article.
4. If airflow meter adjustment does not affect the LEDs, and ECU self-diagnostic system only flashes Code 55 (pass), either airflow meter, oxygen sensor or ECU is defective.

ECU GREEN LED FEEDBACK RESPONSE

FUEL INJECTOR

See appropriate INJECTOR MALFUNCTION diagnostic chart.

Start (ON-OFF switch) signal is used for ECU control of injector(s). See appropriate START SIGNAL diagnostic chart.

INJECTOR RESISTANCE SPECIFICATIONS

AIR REGULATOR

See appropriate AIR REGULATOR diagnostic chart. Measure resistance across regulator valve terminals. Resistance should be about 70-80 ohms.

AUXILIARY AIR CONTROL (AAC) SOLENOID/VALVE

See appropriate AUXILIARY AIR CONTROL (AAC) diagnostic chart. Disconnect AAC Solenoid and check resistance across solenoid terminals. The resistance should be 10 ohms at 68°F (20°C).

FAST IDLE CONTROL DEVICE (FICD)

See appropriate FAST IDLE CONTROL DEVICE (FICD) diagnostic chart.

Start (ON-OFF switch) signal is used for ECU control of air regulator. See appropriate START SIGNAL diagnostic chart.

IGNITION SYSTEM

For ignition system testing, see BASIC TESTING article.

Start (ON-OFF switch) signal is used for ECU control of ignition system. See appropriate START SIGNAL diagnostic chart.

TIMING ADVANCE SYSTEM

Ignition timing advance is controlled by the ECU based upon sensor input signals reflecting ignition timing needs. If timing problems are experienced, inspect input signals for proper operation. See appropriate component or ECU PIN VOLTAGE CHARTS in PIN VOLTAGE CHART S article. Inputs which help control timing include the following

1. Crank angle sensor
2. Airflow meter
3. Engine (coolant) temperature
4. Idle switch in idle position
5. Ignition switch crank signal
6. Battery voltage.

AIR INJECTOR VALVE (AIV)

Apply vacuum to Air Injection Valve (AIV) vacuum motor. (Scheme 28) Apply air to air cleaner side of AIV and make sure air only flows toward exhaust manifold side. Also see appropriate AIR INJECTION VALVE diagnostic chart.

Scheme 28

Remove vacuum lines and electrical connector from solenoid. Remove solenoid from vehicle. Connect hand-held vacuum pump to middle vacuum port of solenoid. Apply battery voltage to solenoid. (Scheme 29) Ensure correct polarity is used or damage to solenoid may result. Apply vacuum. As battery voltage is applied and removed from solenoid, vacuum should alternately bleed from remaining 2 ports.

Scheme 29

FUEL TANK VACUUM RELIEF VALVE

Wipe valve housing clean. Find means to inhale air through cap. A slight resistance accompanied by clicks indicates vacuum relief valve is okay. By further inhaling air, resistance and clicks should disappear. If valve is clogged or if no resistance is felt, replace fuel tank filler cap.

FUEL VAPOR VENT LINE

1. Check all hoses and fuel filler cap for leaks. Disconnect fuel tank vapor hose at canister. Attach "T" fitting, manometer, and shutoff valve to hose. (Scheme 30)
2. Slowly apply air pressure to open shutoff valve until manometer indicates 153/4" (400 mm) water. Close shutoff valve. Remove air supply.
3. Fuel tank and hoses should hold this pressure within 1" (25 mm) of water for 21/2 minutes. If not, repair or replace components as necessary.
4. If pressure holds for 21/2 minutes, remove fuel filler cap. Ensure pressure drops. If not, check hoses and lines for obstructions.

CARBON CANISTER

Remove hose from valve port. Blow through hose. Air should pass through purge and vent lines, but should not pass through vacuum lines. (Scheme 31)

Scheme 30

Scheme 31

FUEL CHECK VALVE

Disconnect hoses from fuel check valve. Apply air on fuel tank side of valve. Resistance should be felt and a portion of air flow should be directed toward fuel tank. Repeat test on carbon canister side of valve. Air should flow freely through valve. If valve does not function as stated, replace check valve.

VACUUM RELIEF FILLER CAP

Wipe cap clean. Apply vacuum from tank side. Slight resistance should be felt and the cap should make distinct clicking noises. As vacuum increases, resistance should decrease and clicking noise should stop. If valve is plugged or no resistance is felt, replace cap as an assembly.

EGR CONTROL SYSTEM

See appropriate EGR CONTROL and EGR FUNCTION diagnostic charts.

EGR BACKPRESSURE TRANSDUCER (PICKUP 2.4L)

Plug one port of the EGR backpressure transducer (EGR-BPT). (Scheme 32)and (Scheme 33). Connect hand-held vacuum pump to remaining EGR vacuum port and apply vacuum. Apply pressure to bottom port. Check for leaks. If there is no leak, replace BPT valve.

Scheme 32

Scheme 33

EGR VALVE SOLENOID (3-PORT)

Remove vacuum lines and electrical connector from solenoid. Remove solenoid from vehicle. Connect hand-held vacuum pump to middle vacuum port of solenoid. Apply battery voltage to solenoid. Ensure correct polarity is used or damage to solenoid may result. Apply vacuum. As battery voltage is applied and removed from solenoid, vacuum should alternately bleed from remaining 2 ports (includes bleed filter). Solenoid resistance should be 30-40 ohms.

Start (ON-OFF switch) signal is used for ECU control of EGR solenoid. See appropriate START SIGNAL diagnostic chart.

POSITIVE CRANKCASE VENTILATION (PCV)

Run engine at idle. Remove ventilation hose from PCV valve. If valve is working properly, a hissing noise should be heard from hose and a strong vacuum should be felt immediately when finger is placed over valve inlet. If not, check hose and hose connections for leaks or obstructions. Repair or replace as necessary.

MISCELLANEOUS CONTROLS

Note. Although some of the controlled devices listed here are not technically engine performance components, they can affect driveability if they malfunction.

RADIATOR (COOLING) FAN CONTROL RELAY(S)

Note. Information on radiator (cooling) fan control for Pathfinder and Pickup is not available from manufacturer.

Scheme 34

DIAGNOSTIC CHARTS

Note. To identify ECU terminals, see WIRING DIAGRAMS article.

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Scheme 61

See also:
• AIRFLOW METER VOLTAGE TEST
• POWER VALVE CONTROL SOLENOID
• RELAYS