P0177: Fuel Composition Sensor Circuit Range/Performance
What to do
Usually driveable. If the vehicle was refuelled somewhere unfamiliar shortly before the code appeared, that is worth reporting.
What this code means
The fuel composition reading is electrically valid but implausible — it may not change after a refuel when the blend clearly did, or it may report a proportion outside what any pump dispenses. Sensor contamination and water in the tank both produce readings of this kind.
Likely causes
Start here
- Faulty fuel composition sensor · moderate
- Fuel contamination · specialist
Less common
- Water in fuel tank · moderate
- Corroded or loose connector · easy
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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