OBD-II Code · Fuel & Air
P0173
Fuel Trim Malfunction (Bank 2)
Severity
medium
Worth booking. It costs fuel, emissions or comfort until it is fixed.
Can you drive it
Only if running normally
A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety.
Indicative cost (USD)
$75–$500
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
Fuel trim on bank 2 is out of range.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
- Rough running
- Poor fuel economy
Likely causes
- Vacuum leakMost common
- Failed MAF
- Bad O2 sensor
- Fuel pressure problem
Read the full diagnostic procedureP0173 is set when the fuel trim on bank 2 falls outside its allowable correction window in either direction — it's the bank-2 equivalent of an out-of…
P0173 is set when the fuel trim on bank 2 falls outside its allowable correction window in either direction — it's the bank-2 equivalent of an out-of-range trim flag and only appears on V-engines or horizontally-opposed engines with two cylinder banks. Unlike P0174 (specifically lean bank 2) or P0175 (specifically rich bank 2), P0173 often gets logged on vehicles whose ECU strategy reports a generic bank-2 trim malfunction without committing to a direction, so step one is always to read live LTFT and STFT on bank 2 with the engine warm at idle to find out whether the system is pushing positive (lean — adding fuel, look for vacuum leaks and MAF issues) or negative (rich — pulling fuel, look for leaking injectors or stuck purge valves). Once direction is known, the diagnostic collapses into the same workflow as P0171/P0174 (lean) or P0172/P0175 (rich): smoke-test the intake first for cracks in the bank-2 intake runner gaskets or boots, check MAF g/sec against spec for the engine size, then fuel-pressure test at the rail (35-55 psi port-injection, much higher for direct-injection). The single highest-yield 10-minute check is comparing bank-1 trims to bank-2 trims — if bank 1 is at +3% and bank 2 is at +22%, the fault is mechanical on bank 2 (bank-specific vacuum leak, clogged bank-2 injector, exhaust leak ahead of the bank-2 upstream O2 sensor) and not a global fuel-delivery problem.
Vehicle-specific patterns2003-2009 Toyota 4Runner / Tundra / GX470 with the 2UZ-FE 4.7L V8 commonly throws P0173 from a cracked rear PCV hose on bank 2 that's tucked under th…
- 2003-2009Toyota 4Runner / Tundra / GX470 with the 2UZ-FE 4.7L V8 commonly throws P0173 from a cracked rear PCV hose on bank 2 that's tucked under the intake plenum and nearly invisible without removing the intake — smoke test reveals it instantly.
- 2008-2014Cadillac CTS / SRX with the 3.6L LFX/LLT V6 throws P0173 along with P0174 from a known intake-manifold sealing issue at the bank-2 side (GM bulletin coverage on cam-cover-to-manifold gaskets).
- 2004-2010Ford Expedition / F-150 with the 5.4L 3-valve Triton throws P0173 frequently from broken intake-manifold runner control valves on bank 2 — the plastic shaft snaps and the runners flap open.
- 2000-2007Mercedes M112/M113 V6/V8 throws P0173 from cracked intake-manifold air-pump check valves that introduce a one-sided vacuum leak. Repair cost typically lands $75-$500 — vacuum-leak fixes at the low end, manifold-gasket or IMRC repairs at the high end.
Look up another code
P0173 — frequently asked
What does a P0173 code mean?
Fuel trim on bank 2 is out of range.
What causes a P0173 code?
Common causes: Vacuum leak; Failed MAF; Bad O2 sensor; Fuel pressure problem.
What are the symptoms of a P0173 code?
Typical symptoms: Check engine light; Rough running; Poor fuel economy.
Is it safe to drive with a P0173 code?
Only if running normally. A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety. Estimated repair: $75-$500.
How do I diagnose a P0173 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
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