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
Fuel Feedback Monitoring Using Mil
- Enter Mode II diagnostics using MIL. See RETRIEVING CODES USING MIL under SELF-DIAGNOSTIC SYSTEM. If engine is started at this stage, MIL will display condition of air/fuel mixture, monitored by the front Heated Oxygen Sensors (HO2S), whether the vehicle is in closed loop or open loop. With engine at normal operating temperature, run engine at about 2000 RPM for 2 minutes under no-load condition. MIL should flash 5 times every 10 seconds indicating normal operating condition of air/fuel mixture monitored by front HO2S(s).
- When MIL is on, it indicates a lean condition. When MIL is off, it indicates a rich condition. MIL switching on and off indicates closed loop operation. If MIL remains on or off, it indicates an open loop condition.
- To switch to opposing HO2S, turn diagnostic test mode selector on PCM fully clockwise, wait 2 seconds and turn mode selector fully counterclockwise. MIL will now indicate changing to opposing HO2S by rapidly flashing and returning to lean/rich cycling. HO2S feedback of the opposing bank HO2S will now be displayed by MIL.
- Repeat step 3 to switch back to original HO2S feedback signal. Switch from bank to bank as necessary. To erase stored DTC information, go to ERASING STORED INFORMATION under SELF-DIAGNOSTIC SYSTEM. To remain in Mode II, turn engine off and immediately turn ignition on.
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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