The largest online repair guide library for every car

About us
Contact support
FAQ
Sign up
Sign in

2018 Q50 3.0t Running Rough, Check Engine Light P0171/P0174

0

Mike T. · rep 0 · May 25, 3:46 AM · 1 replies · solved · Question

Vehicle: 2018 Infiniti Q50 3.0t Luxe

Hey everyone, I'm having some trouble with my 2018 Infiniti Q50 3.0t Luxe. The check engine light came on a few days ago, and the car feels like it's running a bit rough, especially at idle. It also seems to be using more fuel than usual.

I hooked up my OBD-II scanner and pulled codes P0171 and P0174, which indicate System Too Lean (Bank 1) and System Too Lean (Bank 2) respectively. I've heard these can be tricky to diagnose on the Q50s.

What are the common culprits for these codes on this specific model and engine? I'm hoping it's something I can check myself before taking it to a shop. Any advice on where to start looking would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 3:46 AM

0

ClearTheCode admin answer:

Codes P0171 and P0174 on your 2018 Infiniti Q50 3.0t indicate that your engine's air-fuel mixture is too lean on both banks. This means there's too much air or not enough fuel for optimal combustion. Diagnosing this requires a systematic approach.

  1. Vacuum Leaks: This is a very common cause. Inspect all vacuum lines, intake manifold gaskets, and PCV valve for cracks, disconnections, or leaks. A good test is to spray unlit propane or carburetor cleaner around these areas while the engine is running; if the idle changes, you've found a leak. Pay close attention to the intake manifold area and any turbocharger related vacuum lines.
  2. Mass Air Flow (MAF) Sensor: A dirty or faulty MAF sensor can send incorrect air readings to the Engine Control Module (ECM), leading to a lean condition. Try cleaning the MAF sensor with a specialized MAF sensor cleaner. If the problem persists, the sensor may need replacement.
  3. Fuel Delivery Issues:
    • Fuel Filter: While less common on newer vehicles with in-tank filters, a clogged fuel filter can restrict fuel flow.
    • Fuel Pump: A weak fuel pump might not be providing adequate fuel pressure, especially under load. You'd need a fuel pressure gauge to test this.
    • Fuel Injectors: Clogged or faulty fuel injectors can lead to insufficient fuel delivery to cylinders. This usually manifests with misfire codes as well (P030x).
  4. Oxygen Sensors (O2 Sensors): Faulty upstream (pre-catalytic converter) O2 sensors can provide incorrect readings, causing the ECM to incorrectly lean out the mixture. However, since both banks are affected, a single O2 sensor is less likely unless both failed simultaneously, or the root cause is upstream of both sensors.
  5. Exhaust Leaks: Leaks before the upstream O2 sensors can draw in ambient air, tricking the O2 sensors into thinking the engine is running lean and causing the ECM to add more fuel, which isn't the case here. This would typically cause the ECM to enrich the mixture, not lean it out.

When to See a Shop: If cleaning the MAF sensor and a thorough visual inspection for vacuum leaks don't resolve the issue, it's best to take your Q50 to a qualified mechanic. They have specialized diagnostic tools to monitor live data (fuel trims, O2 sensor readings, fuel pressure) which are crucial for accurately pinpointing the problem. Prolonged driving with a lean condition can lead to engine damage, including catalytic converter failure.

Menu

Help & account