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Rough idle, a P0300 code with no cylinder named, and trim stuck positive for weeks. That trio is the classic single-injector problem on the dual-injection 2.5L. The tests below find the weak cylinder in an afternoon.

Parts first. The set of four 35310-2GGA1 injectors for 2020 Tucson, Santa Fe, and Sportage is in stock at $102.07. 35310-2S100 itself is only a reference number, not a stocked listing. The right number for your VIN gets settled through the RFQ below.

Why one bad injector is hard to see

This engine runs two injection systems, and one can cover for the other. Direct injection sprays fuel straight into the cylinder. Port injection sprays into the intake port and keeps the valves clean.

Fuel trim is the extra fuel the computer adds to keep the mixture right. A creeping positive trim is the engine paying for fuel it never received.

• Weak port injector. The direct side covers most of the fuel, so misfire counts stay low while trim climbs.
• Leaking direct injector. Fuel escapes outside the burn, so the cylinder misfires while trim barely moves.

What it feels like

Check the trim number before you buy anything. Positive trim past about ten percent is a fault, not noise.

• Cold idle shake that clears in a minute. Weak port injector.
• Hot restart stumble or fuel smell after shutdown. A leaking injector.
• Oil that stays diluted. Fuel washing down one cylinder wall.
• Trim swinging rich after refueling. A leak path, not a flow problem.

Lean worst at idle usually means unmetered air, such as an intake gasket or a split boot. Lean worst under load means fuel delivery.

Reading the codes

P0300 means a random misfire. P0301 to P0304 name the cylinder, which cuts your suspects from four to one.

P0171 and P0174 are SAE's lean codes: the computer maxed its fuel compensation and the mixture is still lean.

• P0301 plus P0171. The single-injector classic. Balance test the rail, read the plug.
• P0300, no cylinder named, trim near zero. Ignition or mechanical. The fuel system is fine.
• P0300 with both banks leaning. Pump, filter, or vacuum leak. Injectors are the last suspect.
• P0261 to P0271. Wiring codes. Connector, harness, coil — no set of four fixes a wiring fault.

The test ladder, cheapest step first

Run the steps in order. Each one closes the case or removes a whole branch of it.

1. Log fuel trim at warm idle and at 2,500 rpm. Idle-heavy lean means air leak; load-heavy lean means delivery.
2. Pull the per-cylinder misfire counters. A count on one hole turns P0300 into a named cylinder.
3. Run the balance test. The scan tool pulses each injector and measures the pressure drop. A shallow drop means that cylinder is not delivering.
4. Swap the coil and plug to a neighbor. If the misfire follows the parts, ignition was the fault.
5. Read all four plugs as a set. White and blistered reads lean; black and sooty reads leaking.
6. Key on, engine off, and watch the rail pressure. A rail that bleeds down while parked points at a leak.

Before all of it, smoke-test the intake. A stuck purge valve or a cracked boot copies a bad injector exactly.

One number family, the numbers that are real today

Every figure below comes from the live catalog or the listing titles.

Every number on that table sits inside the wider parts catalog. Only the number under the hood changes; the diagnosis does not.

• Four-piece 35310-2G710 set — Sonata 2011-2014 and Optima 2011-2015 2.4L
• Six-piece 35310-3C560 set — Santa Fe, Azera, Sorento, and Sedona 3.3L V6, 2014-2018
• Four-piece 35310-03HA0 set — Kia Niro and Hyundai Ioniq 1.6L, 2017-2020

2S100 against what is actually in stock

Listings disagree: the same 2GGA1 suffix shows against both 2.4L and 2.5L cars, and 2S000 and 2S001 overlap. Two things settle it — the number cast into the old injector, and your VIN. Send both through the request-for-quote page.

If your VIN resolves next to the 2GGA1 number, the four-piece 35310-2GTA1 listing sits in the same family. Anything that does not fit a form goes to support@koeep.com.

When the injectors are not the fault

Both banks leaning with a P0300 is a supply problem. Check pump volume, the filter, and the pressure regulator first.

Circuit codes in the P0261 to P0271 range are electrical. Wiggle the harness at the rail connector to catch it.

• Connector at the injector body. Heat-cycled pins wear; cleaning is free.
• Harness section. A chafe or a broken wire — a repair, not a set of four.
• Injector coil resistance. Only here is a single injector the fix.

Also check the dealer's TSB list — technical service bulletins are the factory's own repair notes. A documented internal leak may close under coverage, not on your card.

• MC-10225470 (2022). Leaking GDI injectors on 2021-2022 Sonata and Santa Fe, certain 2022 Santa Cruz and Tucson 2.5L.
• 23-FL-002H-1. Extended to 2021-2023 Sonata, 2021-2022 Santa Fe, 2021-2023 Tucson.
• MC-10233552 (2023). The GDS steps that name a leaking injector.
• 2025 class action. Leaking injectors, misfires, and stalling on the 2020-2025 2.5L.

Where the same logic crosses platforms

None of these tests are Hyundai-only. The injector guide for the 2014-2018 Silverado and Sierra runs the same pressure-drop test on a V8 rail.

The VIS actuator guide for the 2.0L and 2.4L manifolds covers the air-side fault that copies a misfire.

Frequently asked questions