Engine Controls Self-Diagnostics - Introduction: Diagnosis Nissan Pathfinder II

DIAGNOSTIC TROUBLE CODES (DTC)

The Powertrain Control Module (PCM) monitors several different engine control circuits. If a malfunction occurs, PCM will record a Diagnostic Trouble Code (DTC). The next time engine is started and the same malfunction is detected, PCM will turn on MIL, signaling DTC is in PCM memory.

After 3 consecutive drive cycles without a malfunction, PCM will turn off MIL, however DTC will be stored in PCM memory. If PCM does not detect that fault for 40 drive cycles, DTC will be cleared from PCM memory. PCM will clear a DTC for a misfire or fuel trim malfunction when fault is not detected for 80 drive cycles.

Hard faults cause MIL to illuminate and remain on until the malfunction is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined. If a sensor fails, PCM will use a substitute value in its calculations to continue engine operation. See FAIL-SAFE MODE under SELF-DIAGNOSTIC SYSTEM. In this condition, vehicle is functional, but driveability will be affected.

VISUAL INSPECTION

Before proceeding with self-diagnostics, perform a non-intrusive visual inspection and prepare vehicle as follows

1. Perform all necessary safety precautions to prevent personal injury or vehicle damage.
2. Block drive wheels. Set parking brake. Place shift lever in Park (A/T) or Neutral (M/T). DO NOT move shift lever during test unless specifically directed to do so.
3. Check condition of air cleaner and air ducting.
4. Check all vacuum hoses for leaks, restrictions and proper routing.
5. Check wiring harness connections for corrosion, damaged pins, loose wires and improper routing.
6. Check PCM, sensors and actuators for physical damage.
7. Check engine coolant and oil level.
8. Check battery condition.
9. Check exhaust system for leaks.
10. Turn off all lights and accessories. Ensure vehicle doors are closed when measuring voltage.

Diagnostic Test Mode I

Note. Test modes cannot be switched with engine running. When ignition is turned off, power to PCM will turn off after 5 seconds. PCM will then return to Diagnostic Test Mode I. Ensure test mode selector is in fully counterclockwise position when vehicle is in use.

As a bulb check, light glows when ignition is turned on and engine is not running. When vehicle is started, MIL will turn off, indicating that no malfunctions are detected. If a malfunction is detected while the engine is running, the MIL glows or flashes and a corresponding DTC will be set in PCM memory.

Diagnostic Test Mode II

Note. Test modes cannot be switched with engine running. When ignition is turned off, power to PCM will turn off after 5 seconds. PCM will then return to Diagnostic Test Mode I. Ensure test mode selector is in fully counterclockwise position when vehicle is in use.

Turn ignition on, but leave engine off. Using a small screwdriver, turn diagnostic mode selector on PCM fully clockwise and MIL should turn off. Wait at least 2 seconds, and then turn diagnostic mode selector fully counterclockwise which will enter into Diagnostic Test Mode II. MIL will flash any DTC(s) present. If 2 or more DTCs are displayed, they may be DTC's or 1st trip DTCs. These can be identified by using CONSULT or GST. To erase stored diagnostic information, go to ERASING STORED INFORMATION .

RETRIEVING CODES USING GENERIC SCAN TOOL (GST)

Turn ignition off. Connect scan tool to DLC located under left side dash panel. (Scheme 1) Turn ignition on. Enter program desired on GST screen. Perform each diagnostic mode according to appropriate service procedure displayed on GST. For further information, see the appropriate operation manual supplied by generic scan tool manufacturer.

GST Mode Descriptions Typical GST modes available are listed with a brief definition of there function. These Generic Scan Tool modes were specified in SAE J1979.

Scheme 1

Mode 1: Readiness Test

This mode accesses current emission related data input and output values. In this mode, system status information is also monitored.

Mode 3: Diagnostic Trouble Codes (DTCs)

This mode gains access to emission related DTCs stored by PCM.

Mode 8: EVAP System Testing

This mode can close EVAP system with ignition on (engine off). The following components can be opened or closed

1. EVAP canister vent control can be opened.
2. Vacuum cut valve by-pass valve can be closed.

During the following conditions, mode 8 cannot function

1. Low ambient temperature or low fuel temperature.
2. Low battery voltage.
3. Engine running or ignition switch in the OFF position.
4. Too much pressure applied to EVAP system.

TESTING PROCEDURE

To ensure correct diagnosis and repair, testing should be done in the following sequence

1. Ensure all customer complaints or observations are recorded. Test drive vehicle with customer, when necessary, for malfunction verification.
2. Retrieve and record stored DTCs and freeze frame data stored. Clear freeze frame data and erase DTC(s). See «CLEARING CODES»(ref-91138-S19289434172001030200000) .
3. Recreate conditions in which malfunction occurred to reset DTC. If DTC is detected, go to step 5 . If malfunction is not detected, consider the following conditions to recreate an intermittent malfunction: Drive vehicle on rough road or with engine vibrating at idle (with A/C on). Incident occurs on only extremely hot or cold days. Water may intrude into connectors and cause corrosion between connector terminals. Operate multiple accessories (P/W, P/L, A/C, wipers, lights, etc.). Start vehicle either hot or cold. Wiring harnesses may be checked by gently wiggling wire harness during testing. Relays and sensors may be checked by gently tapping during testing. NOTE: Perform DTCs in order of priority. See «MULTIPLE DTC PRIORITY IDENTIFICATION»(ref-91138-S20074664632001030200000) table. If malfunction is still not detected, go to next step.
4. Perform DTC CONFIRMATION TEST at the beginning of each DTC diagnostic test to set appropriate DTC. See appropriate SELF-DIAGNOSTICS article.
5. If DTC is set, perform appropriate procedure. If DTC does not reset, diagnose malfunction by symptom. See TROUBLE SHOOTING - NO CODES article for diagnosis by symptoms. After performing necessary repairs, go to next step.
6. Rerun test situations which set DTC(s). Retrieve codes and confirm DTC P0000 (System Normal) is detected. Clear DTC(s) from PCM and TCM memory. See «CLEARING CODES»(ref-91138-S19289434172001030200000) .

MULTIPLE DTC PRIORITY IDENTIFICATION (1)

Using Scan Tool

Turn ignition off. Connect scan tool to DLC. (Scheme 1) Turn ignition on. Enter CLEAR CODES or Mode 4 on scan tool.

SYSTEM READINESS TEST (SRT)

Note. SRT procedure was written specifically for use with Nissan's CONSULT diagnostic scan tool. Generic scan tools can be used but may have limited functions.