1999 Infiniti Q45 BaseFACTORY OEM SERVICE PROCEDURE

Power & Ground Circuits (Q45)

  1. Start engine. If engine starts, go to step  3. If engine does not start, crank engine for at least 5 seconds. Perform PCM diagnostic test mode II. If DTC P1320 is present, perform diagnosis for DTC P1320. See SELF-DIAGNOSTICS - Q45 article. If DTC P1320 is not present, go to next step.
  2. Turn ignition on. Measure voltage between ground and PCM harness connector terminal No. 78 by backprobing. See Fig 1 and Fig 2 . If battery voltage exists, go to step  9. If battery voltage does not exist, repair open or short circuit. See appropriate diagram in WIRING DIAGRAMS article.
  3. Turn ignition off. Measure voltage between ground and PCM harness connector terminals No. 56 and 123 by backprobing. See Fig 1 and Fig 2 . If battery voltage exists, go to next step. If battery voltage does not exist, repair open or short circuit. See appropriate diagram in WIRING DIAGRAMS article.
  4. Measure voltage between ground and PCM harness connector terminals No. 130 and 131 by backprobing. While observing voltmeter, turn ignition on and off. Battery voltage should exist for a few seconds after turning ignition off. After a few seconds, voltage should drop to about zero volts. If voltage is as specified, or if battery voltage exists for more than a few seconds, go to step  8. If battery voltage does not exist, go to next step.
  5. Disconnect PCM and ECCS relay harness connectors. See Fig 3. Check continuity of Red/Green wire between ECCS relay harness connector terminal No. 3 and PCM harness connector terminals No. 130 and 131. If continuity exists, go to next step. If continuity does not exist, repair open in Red/Green wire.
  6. Measure voltage between ground and ECCS relay harness connector terminals No. 2 and 5 (White/Blue wires). If battery voltage exists, go to next step. If battery voltage does not exist, repair open or short circuit. See appropriate diagram in WIRING DIAGRAMS article.
  7. Check continuity of White/Blue wire between ECCS relay harness connector terminal No. 1 and PCM harness connector terminal No. 124. If continuity exists, go to next step. If continuity does not exist, repair open in White/Blue wire.
  8. Check ECCS relay. See RELAYS & SOLENOIDS . Replace if necessary. If ECCS relay is okay, go to next step.
  9. Turn ignition off. Loosen and retighten engine ground bolts. See Fig 4. Disconnect PCM harness connector. See Fig 1. Check continuity between ground and PCM harness connector terminals No. 121, 122, 125, 126, 127 and 128. If continuity exists, go to next step. If continuity does not exist, repair open ground circuit.
  10. No problem is indicated at this time. Problem may be intermittent. See TESTING PROCEDURE under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.
Fig 1: Locating PCM Harness Connector (Q45)
G99H08877Courtesy of NISSAN MOTOR CO., U.S.A.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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