P0174 and your Nevada smog check

P0174 rarely travels alone. On many V engines it shows up together with P0171, the same lean condition on the other bank, and that pairing is a clue in itself. This page sets out what the code means, why the pairing matters to whoever repairs the car, and how the smog rules treat it in Washoe County.

At a glance

• SAE J2012 wording for P0174: System too lean (bank 2).
• Seen together with P0171, it suggests a cause both sides of the engine share.
• A lean code with the lamp lit fails the Nevada OBD test for 1996 and newer light-duty vehicles.
• Test early: a pass is good for 90 days, so early testing leaves room for repairs.

Two banks, one computer

A V engine has two rows of cylinders, each with its own exhaust path and front oxygen sensor. The computer keeps a separate fuel correction for each. SAE J2012 gives each bank its own lean code, and the one for the side without cylinder 1 is P0174: System too lean (bank 2).

The code means bank 2 kept reporting extra oxygen in the exhaust and the computer ran out of room to add fuel. Bank 1 has the matching code P0171. The opposite condition, too much fuel, is P0172 on bank 1.

Both banks or just one

When only bank 2 is lean, a repair shop tends to look at things that belong to that side alone. When both P0171 and P0174 are stored, the more likely suspects are things both banks share, like the air flow measurement or the fuel supply. That is a general pattern, not a diagnosis, and a repair shop will confirm it on your vehicle.

Either way, tell the repair shop every code that was stored, not only the one that sent you there. A list of two or three codes together often says more about the cause than any single code does, and it saves time spent chasing the wrong side of the engine.

How the test treats a lean code

The Nevada OBD inspection does not weigh one code against another. If the check engine lamp is on, a 1996 or newer car or light truck fails, and the technician's analyzer sends that result to the DMV.

That failed result is worth having. The DMV calls it a legal document showing why the vehicle fails, and it is required before repair receipts can count toward a waiver. It also lets you request a challenge test at the emissions lab.

Common causes a repair shop checks

We test; a repair shop finds and fixes the fault, and the DMV recommends a 2G licensed authorized station for emissions work. Common causes a repair shop checks include:

• Unmetered air entering through a vacuum leak or intake gasket on bank 2.
• Air flow sensor readings that run low, especially when both banks are lean.
• Fuel pressure or delivery that falls short under load.
• Exhaust leaks near the bank 2 front oxygen sensor.

Getting from code to pass

Plan backward from your registration date.

• Test early in the renewal window. A passing test is valid for 90 days, and the DMV suggests early testing so there is time for repairs.
• With a failed report in hand, get the repair done and keep every receipt.
• Ask the dealer first about federal emissions warranty coverage or a recall if an expensive emission component is involved; federal law covers some for up to 8 years or 80,000 miles.
• Do not clear codes right before the retest. After a repair, drive up to a week under varying conditions so the self-checks finish.

The Washoe waiver, briefly

If the lamp is still lit after repairs, a 1996 or newer light-duty vehicle may qualify for a waiver. Washoe County asks for receipts of at least $200 in parts and labor for related repairs by a 2G station, or at least $200 in related parts bought by the owner within 14 days of the initial test. Take the vehicle, both failed certificates and the receipts to the DMV Emission Lab; the DMV does not charge for the waiver, which lasts one year.