Engine Controls - Tests W/codes Nissan Pathfinder I

INTRODUCTION

If no faults were found while performing BASIC TESTING proceed with self-diagnostics. If no fault codes or only pass codes are present after entering self-diagnostics, proceed to TESTS W/O CODES article for diagnosis by symptom (i.e. ROUGH IDLE, NO START, etc.).

SELF-DIAGNOSTIC SYSTEM DESCRIPTION

The self-diagnostic system is used for diagnosing malfunctions of Electronic Concentrated Control System (ECCS) sensors and actuators. The Electronic Control Unit (ECU) has a number of available diagnostic modes within the computer.

Both models have 5 diagnostic modes. Before selecting any mode of self-diagnosis, always perform BASIC TESTING first. This will eliminate wasted diagnostic time and invalid diagnostic results.

Note. When performing BASIC TESTING , be careful not to erase any diagnostic information stored in the ECU memory.

HARD FAILURES

Hard failures cause CHECK ENGINE light (if equipped) to illuminate and remain on until the malfunction is repaired. If light comes on and remains on (light may flash) during vehicle operation, determine cause of malfunction using diagnostic (code) charts. If a sensor fails, ECU will use a substitute value in its calculations to continue engine operation. In this condition, (fail-safe mode) the vehicle runs but driveability will not be optimum and engine speed is restricted (2000-3000 RPM depending on model).

INTERMITTENT FAILURES

Intermittent failures may cause CHECK ENGINE light (if equipped) to flicker or illuminate and go out after the intermittent fault goes away. The corresponding trouble code, however, will be retained in ECU memory. If related fault does not reoccur within 50 ignition switch operations, related trouble code will be erased from ECU memory. Intermittent failures may be caused by a faulty sensor, connector or wiring problems. See INTERMITTENTS in appropriate TESTS W/O CODES article.

Note. Follow diagnostic routine when testing ECCS. See DIAGNOSTIC ROUTINE table for correct order of procedure.

DIAGNOSTIC ROUTINE

CHECK ENGINE LIGHT

California models & Pathfinder/Pickup with 3.0L engine, are equipped with a CHECK ENGINE light. As a bulb check, light will illuminate when the ignition is on and engine is not running. CHECK ENGINE light will also illuminate when an ECCS fault has been detected. Not all trouble codes activate CHECK ENGINE light.

DIAGNOSTIC MODES

The self-diagnostic system can detect ECCS malfunctions and store related trouble code. Trouble codes, including intermittent codes, are stored in ECU memory and are available for interpretation unless codes have been cleared.

A dual Light Emitting Diodes (LEDs) self-diagnostic system, located on ECU, is used. See SELF-DIAGNOSTIC SYSTEM table. The ECU is located, under the passanger seat.

SELF-DIAGNOSTIC SYSTEM

DUAL LED SYSTEM (5 MODES)

Self-diagnostic system can be operated in one of 5 modes. Modes are manually changed using screwdriver through access port on ECU. With screwdriver turned fully clockwise, inspection lights will begin to flash. Count the number of flashes. First flash is mode I, second flash is mode II, etc. When desired mode has been indicated, turn screwdriver fully counterclockwise. In different modes, Red and Green LED's perform different functions.

MODE I (MALFUNCTION WARNING)

This is the normal vehicle operating mode. Green LED will indicate loop status. If LED is not blinking, vehicle is in open loop or there is a fault with the oxygen sensor or sensor circuit. If LED is blinking, vehicle is in closed loop. If a malfunction occurs in Mode I, Red LED and check engine light (if equipped) will illuminate, indicating an ECCS malfunction has occurred.

MODE II (EXHAUST GAS MONITOR)

In Mode II, both Red and Green LED's are used to monitor air/fuel mixture feedback control. Green LED will function the same as in Mode I. In open loop, Red LED will remain on or off along with Green LED so vehicle must be in closed loop in order for Mode II results to be valid. In closed loop, Red LED will indicate if system is running rich (light off), lean (light on) or if at the ideal air/fuel ratio (blinking synchronized with Green LED).

MODE III (SELF-DIAGNOSTICS)

When Mode III is accessed, codes stored in ECU memory will be flashed by the Green and Red LED's on the side of the ECU. Green light will flash the 10's column digit, while Red LED will flash the 1's column digit. For example: 3 flashes of the Green LED, followed by 5 flashes of the Red LED would indicate a Code 35.

MODE IV (SWITCH CHECK)

This mode is used for checking ECCS switch status. When the idle switch, starter switch or vehicle speed sensor are activated, the Red LED will come on and go off as the status changes.

MODE V (TEST MODE)

Mode V represents a real-time diagnostic test of the crank angle sensor, ignition signal, airflow output signal and fuel pump. This mode is accessed for an in-bay running test of the vehicle. The Red and Green LEDs must be monitored carefully during this test, with special attention paid to the number of flashes before each pause.

The malfunction code will be displayed only once and will not be stored in memory. If Red LED blinks on and off evenly, this indicates a fault in the crank angle sensor. If the Red LED flashes twice before a pause, this indicates a fault in the airflow meter. If the Red LED blinks 3 times before a pause, this indicates a fault in the fuel pump circuit. If the Red LED blinks 4 times before a pause, this indicates a fault in the ignition signal.

ENTERING SELF-DIAGNOSTICS

Note. When engine is running, it is not possible to switch modes. When ignition switch is turned to OFF position, ECU will switch back to Mode I.

1. Turn ignition switch to ON position. Use a screwdriver to turn ECU diagnostic mode selector fully clockwise.
2. Wait for inspection lights to begin flashing. At this time, inspection lights will flash the mode options (i.e. 2 flashes for Mode II, etc.). As soon as inspection light flashes the desired mode number (3 flashes for Mode III), immediately turn mode selector off.
3. If the mode selector is kept in the ON position, the mode selections will continuously cycle (Mode I to Mode II up to Mode V, then cycles to Mode I, etc.) and the process will continue. This will not erase the memory.

Trouble codes are read using the Red and Green LED inspection lights on the side of the ECU. After selecting Mode III, trouble codes corresponding to that mode will start flashing. Trouble codes are indicated by the number of flashes from the ECU Red and Green LED inspection lights. Count the number of flashes. The Red LED indicates the number of tens while the Green LED indicates the number of ones. For example, 3 flashes of the Red LED followed by 2 flashes of the Green LED would indicate code 32.

TROUBLE CODE IDENTIFICATION CHART

TROUBLE CODE IDENTIFICATION CHART

CLEARING CODES

Note. Ensure all diagnostic codes are extracted from the ECU memory before disconnecting battery or switching from Mode III into Mode IV.

MEMORY ERASE

Stored memory will be erased if battery is disconnected or Mode IV is selected after Mode III has been accessed. However, if mode selector on-off switch is turned to ON position for Pathfinder & Pickup, diagnostic modes will continue to cycle, from Mode I to Mode V, and will keep cycling in the same order, until a certain mode is selected. This does not erase the stored memory.

ECU LOCATIONS TABLE

ECU LOCATIONS

SUMMARY

If no hard fault codes (or only pass codes) are present, driveability symptoms exist or intermittent codes exist, proceed to TESTS W/O CODES article for diagnosis by symptom (i.e. ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.

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CODE CHARTS

Note. When code chart step indicates CHECK COMPONENT, see indicated component in SYSTEM/COMP TESTS article.

FINAL STEPS FOR ALL CODE CHARTS

Unless otherwise instructed in code chart, perform the following steps after repair

1. Reinstall any part removed.
2. Erase the self-diagnostic memory.
3. Ensure Code 55 (no malfunction) is displayed in self-diagnostic mode.
4. Test drive vehicle.
5. Perform self-diagnosis.

If code resets, check for damage to ECU pin terminals and connector harness.

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CODE 12: MASS AIRFLOW SENSOR

Note. On 4-cylinder Pickup, test between terminal "C" and ground in step "A". Test between terminal "A" and terminal No. 16 in step "C".

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See also:
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