2020 Range Rover Sport P0171/P0174 - Lean Codes and Rough Idle

ClearTheCode admin answer:

Hello Sarah,

It sounds like you're dealing with a common issue indicated by P0171 and P0174 codes, which point to a lean condition in both engine banks. This means the engine is receiving too much air or not enough fuel for proper combustion. Here's a breakdown of potential causes and troubleshooting steps:

1. Common Causes for P0171/P0174:

   • Vacuum Leaks: This is one of the most frequent culprits. Leaks in intake manifold gaskets, PCV hoses, brake booster lines, or other vacuum lines can introduce unmetered air into the engine.
   • Mass Air Flow (MAF) Sensor: A dirty or faulty MAF sensor can send incorrect air mass readings to the engine control unit (ECU), leading to an improper fuel-air mixture.
   • Fuel Delivery Issues: This could include a weak fuel pump, clogged fuel filter, or dirty fuel injectors. If the fuel pressure is low, the engine will run lean.
   • Oxygen (O2) Sensors: While less common for both banks to go bad simultaneously and cause these specific codes, faulty O2 sensors can sometimes provide inaccurate readings.
   • Exhaust Leaks: Leaks before the O2 sensors can cause them to read incorrectly, leading the ECU to compensate by reducing fuel.

2. Troubleshooting Steps You Can Take:

   • Inspect for Vacuum Leaks: With the engine running, listen for hissing sounds around the intake manifold and vacuum lines. You can also carefully spray unlit propane or a small amount of carb cleaner around suspected areas; if the engine RPM changes, you've found a leak.
   • Clean the MAF Sensor: Disconnect the MAF sensor and carefully spray it with MAF sensor cleaner (never use anything else). Allow it to dry completely before reinstalling.
   • Check Air Filter: Ensure your engine air filter is clean and not obstructed.

3. When to See a Shop:

   • If the above steps don't resolve the issue, or if you're uncomfortable performing these checks yourself, it's best to take your Range Rover Sport to a qualified Land Rover specialist. They have diagnostic tools that can monitor live data (fuel trims, MAF readings, O2 sensor voltages) to pinpoint the exact cause. They can also perform a fuel pressure test and smoke test for vacuum leaks, which are more thorough than visual inspections.
   • Continued driving with a lean condition can lead to long-term engine damage, including catalytic converter failure, so addressing this promptly is important.