5th Gen 4Runner: Check engine light with P0171 or P0174, system too lean

Checks, in order

1. Gas cap and obvious hoses
   Tighten the gas cap and look over the air intake boot, PCV hose and brake booster hose for cracks or loose clamps.
   easy $ · under about $50
2. Clean the MAF sensor
   Remove the sensor and spray only MAF-safe cleaner on the wire element. Never touch the element, and let it dry fully before refitting.
   easy $ · under about $50
3. Check live fuel trims
   With a scan tool, compare short and long term fuel trims at idle and at 2,500 rpm. Trims that are high at idle and improve with rpm suggest a vacuum leak. Trims that stay high suggest air metering or fuel supply.
   medium $ · under about $50
4. Smoke test the intake
   A smoke machine finds small leaks at the intake manifold gaskets and vacuum fittings that you cannot hear. Many independent shops will do this for a modest fee.
   medium $$ · about $50 to $500
5. Fuel pressure test
   If trims are lean under load and the intake is tight, test fuel pressure at the rail against the manual. A weak pump or clogged filter in the tank assembly would be the cause.
   medium $$ · about $50 to $500

Applies to: 5th generation 4Runner, 2010 to 2024, with the 1GR-FE 4.0L V6 and the 5-speed automatic. Assumes the stock configuration; trim-specific items (KDSS, sunroof, A/C) are noted where they apply.

Tools and parts for these checks

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The same problem on other Toyotas

• FJ Cruiser (2007–2014): Check engine light with P0171 or P0174 (system too lean)
• 100 Series Land Cruiser / Lexus LX 470 (1998–2007): Check engine light with P0171, P0174 or air-fuel sensor codes (P2195, P2197)
• Lexus GX 470 (2003–2009): Check engine light with P0171 and P0174 (both banks lean)

Other fuel & ignition problems on the 5th Gen 4Runner

• Rough idle, shaking, or misfire with a flashing check engine light
• Engine cranks but won't start

More 5th Gen 4Runner problems

• Rust on the frame, flaking, or holes in the frame rails (Frame & Body)
• KDSS warning, fluid leak, or clunking and uneven ride on a KDSS truck (Steering & Suspension)
• Oil leak or oil smell from the front of the engine (Engine)
• Check engine light with P0420 or P0430, catalyst efficiency (Emissions)
• Temperature gauge climbing, coolant loss, or overheating (Cooling)
• Turn the key: click or nothing, engine won't crank (Starting & Charging)

All 16 5th Gen 4Runner symptoms in the interactive troubleshooter →

General guidance from owner experience. Confirm torque specs, fluid capacities and procedures in the factory service manual. Brakes, steering and anything structural: if in doubt, have a qualified shop inspect it before driving.