Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1999 Infiniti Q45 BaseFACTORY OEM SERVICE PROCEDURE
Power & Ground Circuits (G20)
- Start engine. If engine starts, go to next step. If engine does not start, turn ignition off and on. Measure voltage between ground and PCM harness connector terminal No. 38 by backprobing. See Fig 1 and Fig 2 . If battery voltage exists, go to step 8. If battery voltage does not exist, go to next step.
- Measure voltage between ground and PCM harness connector terminals No. 70 and 113 by backprobing. 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.
- Measure voltage between ground and PCM harness connector terminals No. 56 and 61 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, go to step 8. If battery voltage does not exist, go to next step. If battery voltage exists for more than a few seconds after ignition is turned off, go to step 7.
- Disconnect PCM and PCM relay harness connectors. See Fig 1 and Fig 3 . Check continuity of White/Red wire between PCM relay harness connector terminal No. 3 and PCM harness connector terminals No. 56 and 61. If continuity exists, go to next step. If continuity does not exist, repair open in White/Red wire.
- Measure voltage between ground and PCM relay harness connector terminals No. 1 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.
- Check continuity of White/Green wire between PCM relay harness connector terminal No. 2 and PCM harness connector terminal No. 4. If continuity does not exist, repair open in White/Green wire. If continuity exists, go to next step.
- Check PCM relay. See RELAYS & SOLENOIDS . Replace if necessary. If PCM relay is okay, go next step.
- Turn ignition off. Disconnect PCM harness connector. Check continuity between ground and PCM harness connector terminals No. 10, 19, 39, 43, 106, 112 and 118. If continuity does not exist, repair open ground circuit. If continuity exists, go to next step.
- No problem is indicated at this time. Problem may be intermittent. See TESTING PROCEDURE under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.
Factory Service Tools
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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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