Why does my Suzuki Verona keep throwing lean codes P0171 and P0174?

Short answer: P0171 and P0174 mean the engine is running lean on both sides: more air is getting in than the computer measured, or not enough fuel. On the Verona, the most common cause is an unmetered air leak. One 2005 owner went to about five shops before a mechanic found an air leak at the back of the engine, and that fixed it. Have someone check the intake boot, intake gaskets and vacuum hoses, and look at fuel trims and freeze-frame data before buying parts.

Symptom: The check engine light comes on with P0171 and P0174. It may go off on rainy days and come back when the air gets dry, or keep coming back after parts were replaced.

What to check first

1. Read the codes and the freeze-frame data. A shop can show fuel trims, which say how hard the computer is adding fuel.
2. Look for air leaks: a torn intake boot between the air filter and throttle body, cracked vacuum hoses and leaking intake gaskets.
3. Listen at idle for a hiss or puffing sound, including at the back of the engine.
4. Check for exhaust leaks ahead of the upstream oxygen sensor. These can also set lean codes.
5. Have fuel pressure checked if no leaks are found.

Likely causes

1. Air leak behind the engine (intake side). The fix for the 2005 car after about five shops missed it.
2. Torn intake boot or leaking intake manifold gasket. A member said both codes together usually mean an air leak between the air filter and the throttle body, or an intake gasket.
3. Exhaust leak ahead of the front oxygen sensor. Another cause of lean codes members listed.
4. Weak fuel supply. Less common, but lean means too little fuel as well as too much air.

What it usually costs

The 2005 owner said a dealer quoted several hours of diagnosis (maybe $1,000) plus $1,500–$2,000 for repairs. The final fix was an air leak found by a better independent mechanic, and the owner didn't post that price.

Is it safe to keep driving?

Lean codes usually don't mean you must stop driving, but a lean engine can run rough, hesitate and fail emissions. If the light flashes or it runs badly, park it. Verify with a mechanic.

DIY or shop?

DIY for looking and listening. Checking the intake boot and hoses is easy. A smoke test for hidden leaks is best done by a shop.

Recalls, bulletins and complaints in plain words

• Related recalls: NHTSA lists these recalls touching this area of the Suzuki Verona: 04V396000 (2004-2004 model years, fuel system, gasoline). Check your VIN at nhtsa.gov/recalls. If your car is part of this recall, the dealer fixes it for free.
• Plain words: Recall 04V396000 covered 2004 Veronas whose engine computer could run the engine too lean when slowing down, which can make it stall. That's closely related to lean codes, so check your VIN first. If your car is part of this recall, the dealer fixes it for free. Verify with a mechanic.
• NHTSA complaints: 115 keyword-matched complaints for Suzuki Verona 2004–2006 (of 216 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-27; keywords: check engine, engine light, lean, vacuum, leak, P0171, P0174, idle, stall, rough, hesitation). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In Check engine light suzuki verona on Car Talk, a 2004 Verona's check engine light kept coming back after a repair, oddly going off when it rained and on when the air was dry. The codes were P0171 and P0174. A member explained that means both sides of the engine are running lean, usually from extra air getting in that the computer doesn't measure.
• In Suzuki Verona 05 on Car Talk, a 2005 owner had been to about five shops for P0171 and P0174, and a dealer quoted a long diagnosis plus $1,500–$2,000 in repairs. Members said both codes together usually mean an air leak, a leaking intake gasket or an exhaust leak, and that the freeze-frame and fuel trim data are the place to start. The owner later reported that a new mechanic found an air leak behind the engine and fixed it.

Quick tip

Lean codes are a leak hunt. A shop with a smoke machine can find in 20 minutes what parts-swapping misses for months.

Vehicle focus: 2004–2006 Suzuki Verona, 2.5L inline-six.

Safety / mechanic note

Keep hands and loose clothing away from belts when listening for leaks with the engine running. Verify with a mechanic.