The 1GR-FE 4.0L V6 is one of the most reliable engines Toyota builds, and the one weak spot on 5th gen 4Runners is the secondary air injection (AI) system — the P2440/P2441 codes that throw a check engine light around 80,000–120,000 miles. Beyond that, this engine asks only for its scheduled fluids and plugs and routinely runs past 250,000 miles.
The 1GR-FE is a timing-chain V6 (no belt to replace) used across the 4Runner, Tacoma, FJ Cruiser, and others. It is genuinely durable, and most "problems" people report are normal wear items handled on schedule. The exception worth knowing about before you buy or while you own one is the secondary air injection system. On 5th gen trucks it's a cold-start emissions device — an air pump and a pair of switching valves — and the valves stick or corrode, the pump fails, and you get a P2440 or P2441 and a check engine light. It does not affect drivability or reliability, but it will fail an emissions test (relevant in Phoenix's emissions counties) and the OEM repair is not cheap.
The rest of the engine's maintenance story is short. Spark plugs are iridium and last around 100,000–120,000 miles. The PCV valve and valve cover gaskets are the usual minor oil-seepage items at higher mileage. Keep the oil changed on schedule and the cooling system on Toyota's SLLC, and the 1GR-FE is about as worry-free as a trail engine gets.
An OBD2 scanner to read and confirm codes, a basic socket set, and a torque wrench for plug and cover work. For the AI system specifically, the OEM pump-and-valve assembly or a quality aftermarket equivalent. For routine work, Denso iridium plugs and OEM PCV and gasket parts.
1. Scan any check engine light and record the exact code before throwing parts at it
2. For P2440/P2441, confirm whether it's a stuck switching valve (sometimes cleanable) or a failed pump — bench-test the pump for operation
3. Replace the AI valves and/or pump assembly with the engine cold; torque the manifold and bracket fasteners to spec
4. Clear the code and complete a cold-start drive cycle to confirm the monitor passes — emissions testing requires the readiness monitor set
5. For routine maintenance, replace iridium plugs at interval and gap-check before install (they come pre-gapped — verify, don't bend the tip)
6. Inspect the PCV valve and valve cover gaskets at higher mileage for oil seepage and replace as needed
Don't ignore the AI code as "emissions" if you live in an emissions-test county — you won't pass inspection with the monitor incomplete. Some owners delete or bypass the AI system; that is not emissions-legal for a registered street vehicle and can itself trip codes, so weigh it against your local rules. On spark plugs, the rear bank requires removing the intake on the 1GR-FE, so it's a few hours of work, not minutes — budget the time. Watch oil consumption above 150,000 miles; a modest increase is normal, but a sudden jump with blue smoke points to valve seals or rings and deserves a compression and leak-down test before any trail trip.
The AI pump-and-valve repair runs $300–$400 in parts (OEM) and $200+ in labor if you farm it out, so call it $300–$600 turn-key. A full iridium plug set is about $60 in parts; the labor is the intake removal time. PCV and valve cover gaskets are around $70 in parts. None of this is recurring at short intervals — the 1GR-FE's running cost over a decade is low, which is exactly why it's the engine to look for in a used 4Runner.
| Part | Vendor | Est. price |
|---|---|---|
| Secondary Air Injection (AI) Pump and Valve Assembly | Toyota / Dorman | ~$320 |
| Denso Iridium Spark Plugs (set of 6, 1GR-FE) | Denso | ~$60 |
| OEM Toyota PCV Valve and Valve Cover Gasket Set | Toyota | ~$70 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.