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Engine Controls - Self-Diagnostics - Introduction - Q45: Diagnosis Infiniti Q45 II

Testing & Diagnostics ~874 words

DIAGNOSTIC TROUBLE CODES (DTC)

The Engine 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 SELF-DIAGNOSTICS - TESTING article.

VISUAL INSPECTION

Before proceeding with self-diagnostics, perform a non-intrusive visually 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

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

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.

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 or open EVAP system components, with ignition switch in the ON position, 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-18059-S40501561062000122900000) .
  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: Vehicle Vibration Drive vehicle on rough road or with engine vibrating at idle (with A/C on). Heat Or Cold Sensitive Incident occurs on only extremely hot or cold days. Water Intrusion Water may intrude into connectors and cause corrosion between connector terminals. Electrical Load Operate multiple accessories (P/W, P/L, A/C, wipers, lights, etc.). Hot Or Cold Start Start vehicle either hot or cold. Poor Connections Wiring harnesses may be checked by gently wiggling wire harness during testing. Relays and sensors may be checked by gently tapping during testing. If malfunction is still not detected, go to next step. NOTE: Perform DTCs in order of priority. See MULTIPULE DTC PRIORITY IDENTIFICATION.
  4. Perform malfunction confirmation procedure (if available) at the beginning of each DTC diagnostic test to set appropriate DTC. See «SELF-DIAGNOSTICS - TESTING»(ref-18056) article.
  5. If DTC is set, perform appropriate procedure. If DTC does not reset, diagnose malfunction by symptom. See «TESTS W/O CODES»(ref-18053) 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-18059-S40501561062000122900000) .

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.

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