P0170
Fuel Trim Malfunction (Bank 1)
P0170 means the engine computer is making an unusually large fuel adjustment on bank 1 and is no longer happy with the result. The engine may be getting too much air, not enough fuel, or misleading sensor data. Common causes include vacuum leaks, MAF errors, fuel pressure problems, injector faults, or oxygen-sensor feedback that does not match reality.
- SEV
- 3/5
- DRIVE
- CAUTION
- DIY
- $20-$250
- SHOP
- $120-$900
Quick answer
AI-CITATION READYWhat it means
Can you drive with it?
Most common causes
- Vacuum leak or other unmetered air entering the intake on bank 1
- Mass air flow sensor contamination or incorrect airflow calculation
- Low fuel pressure, restricted fuel filter, or weak fuel pump
Typical repair cost
DIY usually runs $20-$250. Typical shop repair lands around $120-$900, depending on the root cause.
01 / Definition
P0170 means the powertrain control module has detected that bank 1 fuel trim is outside the expected correction range or is behaving irrationally for the operating conditions. Fuel trim is the PCM's running adjustment to keep the air-fuel mixture near target. This fault often comes from unmetered air, weak fuel delivery, injector imbalance, bad airflow or oxygen-sensor input, or a wiring or software problem that makes the trim calculations unreliable.
02 / Drive status
With caution. You can usually drive short distances, but expect rough running, hesitation, poor fuel economy, or a possible stall if the mixture problem gets worse. Avoid long trips or heavy load until the fuel trim data and root cause are checked.
03 / Symptoms
- Check engine light
- Rough idle
- Hesitation on acceleration
- Loss of power
- Poor fuel economy
- Hard starting
- Possible stall at idle or after a stop
04 / Causes
| 1 | Vacuum leak or other unmetered air entering the intake on bank 1 | high |
|---|---|---|
| 2 | Mass air flow sensor contamination or incorrect airflow calculation | high |
| 3 | Low fuel pressure, restricted fuel filter, or weak fuel pump | medium |
| 4 | Dirty, restricted, or leaking fuel injector on bank 1 | medium |
| 5 | Front oxygen sensor or air-fuel sensor feedback that is biased or slow | medium |
| 6 | Wiring, connector, or ground problem affecting trim-related sensors | medium |
| 7 | PCM software issue or adaptation problem after other faults | low |
05 / Diagnostic sequence
- 01Scan for other stored or pending codes first, especially lean, rich, MAF, misfire, or oxygen-sensor faults.
- 02Review short-term and long-term fuel trims at idle, light cruise, and under load so you can tell whether the correction pattern points to air, fuel, or sensor error.
- 03Inspect intake hoses, PCV plumbing, manifold sealing, and vacuum connections for leaks or loose fittings on bank 1.
- 04Check mass air flow sensor readings and inspect the air filter and intake path for contamination or leaks after the MAF.
- 05Test fuel pressure and fuel delivery volume, then compare the results to specification before blaming sensors.
- 06Check injector performance and cylinder balance on bank 1 if trim data suggests one side of the engine is carrying the problem.
- 07Review front oxygen-sensor or air-fuel sensor switching behavior and inspect wiring, grounds, and connector condition.
- 08Clear the code only after repairs and confirm the fuel trims return to a stable range during a road test.
06 / Repairs
| 1 | Repair vacuum leaks, intake leaks, or PCV faults that are pushing bank 1 trim out of range | $20-$350 |
|---|---|---|
| 2 | Clean or replace a contaminated mass air flow sensor and correct any intake-path problems | $15-$250 |
| 3 | Restore fuel pressure or injector performance by servicing the filter, pump, regulator, or injectors as testing requires | $50-$900 |
| 4 | Replace a biased front oxygen sensor or repair its wiring if live data proves the feedback signal is unreliable | $80-$350 |
| 5 | Update PCM software or complete adaptation relearn procedures if the mechanical and sensor faults have already been corrected | $0-$200 |
07 / Related codes
08 / FAQ
What does P0170 mean?
It means the PCM is no longer satisfied with the fuel trim correction on bank 1 and sees the adjustment as out of range or irrational.
Is P0170 the same as a lean code?
Not exactly. It often overlaps with lean or rich conditions, but P0170 points more broadly to a fuel-trim control problem on bank 1.
Can a vacuum leak cause P0170?
Yes. Unmetered air is one of the most common reasons bank 1 fuel trim moves far enough to trigger this code.
Can a bad MAF sensor cause P0170?
Yes. If airflow data is wrong, the PCM may command the wrong amount of fuel and run out of trim authority.
Can I drive with P0170?
Usually for short trips with caution, but the engine may hesitate, idle poorly, or stall if the mixture problem becomes more severe.
09 / Source and method
- DATA BASIS
- OBD-II REFERENCE + OBD2.HELP
- METHOD
- STATIC VALIDATION
- SAFETY
- INFORMATIONAL
This page combines OBD-II diagnostic reference data with OBD2.help generated diagnostic guidance for code meaning, likely causes, and repair direction.
Publishing uses deterministic schema and build validation, plus manual spot checks on representative pages before release.
Safety-critical diagnosis and repairs should be confirmed with a qualified mechanic, especially when the vehicle is misfiring, overheating, or losing power.