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Home >> Nissan-Datsun >> 2003 >> Sentra Limited >> Repair and Diagnosis >> External Pages >> Different car >> Section 41 (Engine Controls - Self-Diagnostics - Quest) >> Diagnostic Tests >> DTC P0171 Or DTC P0172: Fuel Injection System Function >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2002 Nissan Quest. However, it is still accessible from the selected car via links, so may be relevant.
  1. Start engine and let it idle. Check for leaks in exhaust system before 3-way catalyst. Check intake system for leaks. If problem exists, repair or replace faulty components as necessary and retest system. If problem does not exist, go to next step.
  2. Turn ignition off. Disconnect front HO2S harness connector located near oil filler cap. Disconnect ECM harness connector. See Figure. Check continuity of Light Green wire between ECM harness connector terminal No. 50 and front HO2S harness connector terminal No. 2. See Figure. Continuity should exist. Also, check circuit for short to ground and short to voltage. Repair circuit as necessary and retest system. If circuit is okay, go to next step.
  3. Reconnect all harness connectors. Check fuel pressure. See BASIC DIAGNOSTIC PROCEDURES article. Fuel pressure should be 34 psi (2.4 kg/cm2 ) with vacuum hose connected to fuel pressure regulator. Fuel pressure should be 43 psi (3.0 kg/cm2 ) with vacuum hose disconnected from fuel pressure regulator. If fuel pressure is not as specified, repair fuel system as necessary. If fuel pressure is as specified, go to next step.
  4. Start engine and let it idle. Using scan tool, check MAF sensor signal. At idle, value should be 3.3-4.8 gm/sec. At 2500 RPM, value should be 12.0-14.9 gm/sec. If values are as specified, go to next step. If values are not as specified, repair MAF sensor or circuit. See DTC P0100: MASS AIRFLOW SENSOR .
  5. With engine idling, listen to each injector for clicking noise. If any injector does not click, repair circuit or replace injector as necessary. See SYSTEM & COMPONENT TESTING article. If all injectors click, go to next step.
    6. NOTE: Install NEW "O" rings on all fuel injectors once removed.
  6. Turn ignition off and allow engine to cool. Ensure no fire hazards exist and remove fuel injector assembly with fuel lines and harness connectors connected. Place a suitable cup under each fuel injector to collect fuel. Disconnect all ignition coil harness connectors. Turn ignition on. Verify fuel is not dripping from fuel injectors. Replace fuel injectors which are leaking. Crank engine for 3 seconds and ensure each fuel injector sprays fuel. Replace injector(s) that do not spray fuel. If all injectors are okay, go to next step.
  7. No problem is indicated at this time. Problem may be intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article.
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