P0179 — Fuel Composition Sensor Circuit High Input
Drive with caution — fix soon.
What P0179 means
This code means the voltage in the fuel composition sensor circuit has risen above the normal range, signaling a high input. It's usually caused by a short to voltage in the wiring, an open circuit, a poor connector, or a failed sensor. It's generally a sensor or wiring fault and is fixable once a technician inspects the circuit and tests the sensor.
Common symptoms
- Check engine light is on
- Rough idle or slight engine shaking
- Reduced fuel economy
- Engine hesitation after refueling
- Slightly reduced power
Common causes
- Short to voltage in the sensor wiring
- Open circuit in the sensor wiring
- Failed fuel composition (flex-fuel) sensor
- Corroded or loose connector at the sensor
- Faulty engine control module (rare)
Typical repair cost
$120 – $500
Varies by vehicle and root cause.
Frequently asked questions
Can I keep driving with a P0179 code?
Usually yes. The car typically still runs, but the fuel mixture may be slightly off, so it's best to have it diagnosed within a week or two to avoid rough running or wasted fuel.
How much does it cost to fix a P0179?
A wiring or connector repair may be around $120, while replacing the fuel composition sensor with parts and labor can reach about $500.
Is a P0179 code serious?
It's moderate. It rarely strands you, but the engine needs accurate fuel readings, so fixing it helps avoid drivability problems and poor fuel economy.
What does 'high input' mean for this sensor?
It means the circuit voltage is higher than normal, often from a short to power or an open circuit. The computer flags it because it can no longer trust the ethanol reading.