P0173: Fuel Trim Malfunction (Bank 2)

P0173 means the ECU has pushed long-term fuel trim on Bank 2 to the limit of its correction range and still cannot maintain the target air-fuel ratio. Because P0173 only affects one bank, it usually points to something specific to Bank 2 (a leak, a degraded sensor, or a dirty injector on that bank) rather than a whole-engine issue like a clogged fuel filter that would affect both banks.

P0173 is a fuel system-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0173 and illuminates the check engine light.

If your vehicle has triggered P0173, you may notice one or more of these symptoms:

• Check engine light on
• Rough or uneven idle, especially in Park or Neutral
• Slight hesitation during acceleration
• Reduced fuel economy on one bank
• Possible faint fuel or sulfur smell from the exhaust

Here are the most common causes of P0173, ranked by how likely they are to be the culprit:

Generally yes, for short-term driving. The engine can typically still be driven, but a fuel trim out of range on one bank degrades fuel economy and risks catalytic converter damage over time. Fix within a couple of weeks.

Follow these steps to pinpoint the root cause of P0173:

1. Read live data: focus on short-term and long-term fuel trim for Bank 2. A long-term trim above +20% or below -20% confirms the bank has been hitting its limits
2. Compare Bank 2 trims to Bank 1. If only Bank 2 is out of range, the cause is bank-specific (one injector, one sensor, one manifold gasket section)
3. Smoke-test the intake on Bank 2 specifically. On V engines, intake manifold gaskets fail one side at a time as plastic shrinks unevenly
4. Swap the upstream sensors between banks and re-check live data. If the high trim follows the sensor, replace it; if it stays on the original bank, focus on mechanical causes
5. Inspect for exhaust leaks ahead of the Bank 2 upstream sensor. A small leak can pull fresh air into the exhaust stream and trick the sensor into reading lean

Repair costs for P0173 vary depending on the root cause and your vehicle. Here are typical estimates:

P0173 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:

These codes are often seen alongside P0173 or indicate related issues: